individualistic hypothesis definition biology

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There are a number of possible interspecific interactions that link the species of a community.
0 indicates that a population is not affected by the interaction.
The effect of an interaction between two species may change as circumstances change.
When two species compete for a resource, the result is detrimental to one or both species (?/?)
The competitive exclusion principle states that two species with similar needs for the same limiting resources cannot coexist in the same place.
In the analogy stated by ecologist Eugene Odum, an organism’s habitat is its “address,” and the niche is the organism’s “profession.”
For example, the niche of a tropical tree lizard includes the temperature range it tolerates, the size of branches it perches on, the time of day when it is active, and the kind of insects it eats.
The competitive exclusion principle can be restated to say that two species cannot coexist in a community if their niches are identical.
However, ecologically similar species can coexist in a community if their niches differ in one or more significant ways.
The fundamental niche may differ from the realized niche, the niche a species actually occupies in a particular environment.
Resource partitioning is the differentiation of niches that enables two similar species to coexist in a community.
Character displacement is the tendency for characteristics to be more divergent in sympatric populations of two species than in allopatric populations of the same two species.
Predation is a +/- interaction between species in which one species, the predator, kills and eats the other, the prey.
This interaction also includes interactions such as seed predation, in which seed-eating weevils eat plant seeds.
Predators have many feeding adaptations, including acute senses and weaponry such as claws, fangs, stingers, or poison to help catch and subdue prey.
Predators that pursue prey are generally fast and agile; those who lie in ambush are often camouflaged.
Behavioral defenses include fleeing, hiding, and self-defense.
Alarm calls may summon many individuals of the prey species to mob the predator.
Camouflage or cryptic coloration makes prey difficult to spot against the background.
Chemical defenses include odors and toxins.
Predators are cautious in approaching potential prey with bright coloration.
In Batesian mimicry a harmless, palatable species mimics a harmful, unpalatable model.
Each species gains an additional advantage because predators are more likely to encounter an unpalatable prey and learn to avoid prey with that appearance.
Some snapping turtles have tongues resembling wiggling worms to lure small fish.
Herbivores include large mammals and small invertebrates.
Many herbivorous insects have chemical sensors on their feet to recognize appropriate food plants.
Mammalian herbivores have specialized dentition and digestive systems to process vegetation.
Plants may produce chemical toxins, which may act in combination with spines and thorns to prevent herbivory.
Endoparasites live within the body of the host; ectoparasites live and feed on the external surface of the host.
The larvae feed on the body of the host, eventually killing it.
Many parasites have complex life cycles involving a number of hosts.
Some parasites change the behavior of their hosts in ways that increase the probability of the parasite being transferred from one host to another.
Parasites can have significant direct and indirect effects on the survival, reproduction, and density of their host populations.
Pathogens are typically bacteria, viruses, or protists.
Fungi and prions can also be pathogenic.
Many pathogens are lethal.
Examples of mutualism include nitrogen fixation by bacteria in the root nodules of legumes; digestion of cellulose by microorganisms in the guts of ruminant mammals; and the exchange of nutrients in mycorrhizae, the association of fungi and plant roots.
Mutualistic interactions may result in the evolution of related adaptations in both species.
Commensal interactions are difficult to document in nature because any close association between species likely affects both species, if only slightly.
The hitchhiking barnacles gain access to a substrate and seem to have little effect on the whale.
However, the barnacles may slightly reduce the host’s efficiency of movement.
Conversely, they may provide some camouflage.
A change in one species acts as a selective force on another species, whose adaptation in turn acts as a selective force on the first species.
An example is the gene-for-gene recognition between a plant species and a species of virulent pathogen.
These are adaptations to other organisms in the community rather than coupled genetic changes in two interacting species.

Concept 53.2 Dominant and keystone species exert strong controls on community structure

Species diversity is a fundamental aspect of community structure.

A small number of species in the community exert strong control on that community’s structure, especially on the composition, relative abundance, and diversity of species.
The species diversity of a community is the variety of different kinds of organisms that make up the community.
Species richness is the total number of different species in the community.
The relative abundance of the different species is the proportion each species represents of the total individuals in the community.
Species diversity is dependent on both species richness and relative abundance.

Trophic structure is a key factor in community dynamics.

The trophic structure of a community is determined by the feeding relationships between organisms.
The transfer of food energy up the trophic levels from its source in autotrophs (usually photosynthetic organisms) through herbivores (primary consumers) and carnivores (secondary and tertiary consumers) and eventually to decomposers is called a food chain.
A food web uses arrows to link species according to who eats whom in a community.
A given species may weave into the web at more than one trophic level.
For example, phytoplankton can be grouped as primary producers in an aquatic food web.
A second way to simplify a food web is to isolate a portion of the web that interacts little with the rest of the community.
Charles Elton pointed out that the length of most food chains is only four or five links.
Only about 10% of the energy stored in the organic matter of each trophic level is converted to organic matter at the next trophic level.
The energetic hypothesis predicts that food chains should be relatively longer in habitats with higher photosynthetic productivity.
In a variable environment, top predators must be able to recover from environmental shocks that can reduce the food supply all the way up the food chain.
The dynamic stability hypothesis predicts that food chains should be shorter in unpredictable environments.
Most of the available data supports the energetic hypothesis.
Another factor that may limit the length of food chains is that, with the exception of parasites, animals tend to be larger at successive trophic levels.
The exaggerated impact of these species may occur through their trophic interactions or through their influences on the physical environment.
Dominant species are those species in a community that are most abundant or have the highest biomass (the sum weight of all individuals in a population).
One hypothesis suggests that dominant species are competitively successful at exploiting limiting resources.
This could explain why invasive species can achieve such high biomass in their new environments, in the absence of their natural predators and pathogens.
One way to investigate the impact of a dominant species is to remove it from the community.
They influence community structure by their key ecological niches.
Ecologist Robert Paine of the University of Washington first developed the concept of keystone species.
Pisaster is a predator on mussels such as Mytilus californianus, a superior competitor for space in the intertidal areas.
After Paine removed Pisaster, the mussels were able to monopolize space and exclude other invertebrates and algae from attachment sites.
When sea stars were present, 15 to 20 species of invertebrates and algae occurred in the intertidal zone.
After experimental removal of Pisaster, species diversity declined to fewer than 5 species.
Pisaster thus acts as a keystone species, exerting an influence on community structure that is disproportionate to its abundance.
An example of such a species is the beaver, which transforms landscapes by felling trees and building dams.
These influential species act as facilitators, with positive effects on the survival and reproduction of other species.

The structure of a community may be controlled from the bottom up by nutrients or from the top down by predators.

V --> H V <-- H V <----> H
Arrows indicate that a change in biomass at one trophic level causes a change in biomass at in the other trophic level.
A simplified bottom-up model is N --> V --> H --> P.
Predators limit herbivores, which limit plants, which limit nutrient levels through the uptake of nutrients during growth and reproduction.
A simplified top-down model is thus N <-- V <-- H <-- P.
The top-down control of community structure is also called the trophic cascade model.
The effect of any manipulation thus moves down the trophic structure as a series of +/? effects.
For example, all interactions between trophic levels may be reciprocal (<-- -->).
The direction of interaction may alternate over time.
Communities vary in their relative degree of bottom-up and top-down control.
Pollution has degraded freshwater lakes in many countries.
This strategy is called biomanipulation.
In lakes with three trophic levels, removing fish may improve water quality by increasing zooplankton and thus decreasing algal populations.
In lakes with four trophic levels, adding top predators will have the same effect.

Concept 53.3 Disturbance influences species diversity and composition

Many communities seem to be characterized by change rather than stability.
The nonequilibrium model proposes that communities constantly change following a disturbance.
Storms, fires, floods, droughts, frosts, human activities, or overgrazing can be disturbances.
Disturbances can create opportunities for species that have not previously occupied habitat in a community.
Small-scale disturbances can enhance environmental patchiness and thus maintain species diversity in a community.
The intermediate disturbance hypothesis suggest that moderate levels of disturbance can create conditions that foster greater species diversity than low or high levels of disturbance.
Frequent small-scale disturbances may prevent a large-scale disturbance.

Humans are the most widespread agents of disturbance.

Agricultural development has disrupted the vast grasslands of the North American prairie.
Logging and clearing for urban development have reduced large tracts of forest to small patches of disconnected woodlots throughout North America and Europe.
Tropical rain forests are disappearing due to clear-cutting.

Ecological succession is the sequence of community changes after a disturbance.

Ecological succession is the transition in species composition in disturbed areas over ecological time.
Initially, only autotrophic prokaryotes may be present.
Next, mosses and lichens colonize and cause the development of soil.
Once soil is present, grasses, shrubs, and trees sprout from seeds blown or carried in from nearby areas.
Herbaceous species grow first, from wind-blown or animal-borne seeds.
Woody shrubs replace the herbaceous species, and they in turn are replaced by forest trees.
For example, early herbaceous species may increase soil fertility.
Early species may inhibit establishment of later species.
Early species may tolerate later species but neither hinder nor help their colonization.

Concept 53.4 Biogeographic factors affect community biodiversity

Two key factors correlated with a community’s biodiversity (species diversity) are its geographic location and its size.
They also noted that small or remote islands have fewer species than large islands or those near continents.

Species richness generally declines along an equatorial-polar gradient.

Tropical habitats support much larger numbers of species of organisms than do temperate and polar regions.
The two key factors are probably evolutionary history and climate.
Tropical communities are generally older than temperate or polar communities.
Biological time thus runs five times faster in the tropics.
Repeated glaciation events have eliminated many temperate and polar communities.
Actual evapotranspiration, determined by the amount of solar radiation, temperature, and water availability, is much higher in hot areas with abundant rainfall than in areas with low temperatures or precipitation.
Potential evapotranspiration, a measure of energy availability, is determined by the amount of solar radiation and temperature.
The species richness of plants and animals correlates with both measures of evapotranspiration.

Species richness is related to a community’s geographic size.

Larger areas offer a greater diversity of habitats and microhabitats than smaller areas.

Species richness on islands depends on island size and distance from the mainland.

Because of their size and isolation, islands provide excellent opportunities for studying some of the biogeographic factors that affect the species diversity of communities.
“Islands” include oceanic islands as well as habitat islands on land, such as lakes, mountain peaks, or natural woodland fragments.
An island is thus any patch surrounded by an environment unsuitable for the “island” species.
Robert MacArthur and E. O. Wilson developed a general hypothesis of island biogeography to identify the key determinants of species diversity on an island with a given set of physical characteristics.
Imagine a newly formed oceanic island that receives colonizing species from a distant mainland.
The rate at which new species immigrate to the island.
The rate at which species become extinct on the island.
Its distance from the mainland.
Small islands have lower immigration rates because potential colonizers are less likely to happen upon them.
Small islands have higher extinction rates because they have fewer resources and less diverse habitats for colonizing species to partition.
Islands closer to the mainland will have a higher immigration rate than islands that are farther away.
Arriving colonists of a particular species will reduce the chance that the species will go extinct.
As the number of species increases, any individual reaching the island is less likely to represent a new species.
As more species are present, extinction rates increase because of the greater likelihood of competitive exclusion.
The number of species at this equilibrium point is correlated with the island’s size and distance from the mainland.
Studies of plants and animals on many island chains, including the Galapagos, support these predictions.
Over longer periods, abiotic disturbances such as storms, adaptive evolutionary changes, and speciation may alter species composition and community structure on islands.

Concept 53.5 Contrasting views of community structure are the subject of continuing debate

The community functions as an integrated unit, as a superorganism.
The individualistic hypothesis of community structure depicts a community as a chance assemblage of species found in the same area because they happen to have similar abiotic requirements for rainfall, temperature, or soil type.
The integrated hypothesis emphasizes assemblages of species as the essential units for understanding the interactions and distributions of species.
The individualistic hypothesis emphasizes single species.
The integrated hypothesis predicts that species should be clustered into discrete communities with noticeable boundaries because the presence or absence of a particular species is largely governed by the presence or absence of other species.
The individualistic hypothesis predicts that communities should generally lack discrete geographic boundaries because each species has an independent, individualistic, distribution along the environmental gradient.

The debate continues with the rivet and redundancy models.

The individualistic hypothesis is generally accepted by plant ecologists.
Further debate arises when these ideas are applied to animals.
American ecologists Anne and Paul Ehrlich proposed the rivet model of communities.
Reducing or increasing the abundance of one species in a community will affect many other species.
Species operate independently, and an increase or decrease in one species in a community has little effect on other species.
In this sense, species in a community are redundant.
If a predator disappears, another predatory species will take its place as a consumer of specific prey.
We still do not have enough information to answer the fundamental questions raised by these models: Are communities loose associations of species or highly integrated units?
To fully assess these models, we need to study how species interact in communities and how tight these interactions are.

Lecture Outline for Campbell/Reece Biology, 7th Edition, © Pearson Education, Inc. 53-1

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In This Article Expand or collapse the "in this article" section Henry Allan Gleason

Introduction, plant ecology and geography in the united states before gleason.

Statistical and Quantitative Publications
Other Publications
Early Responses to the Individualistic Hypothesis
Reassessment of the Individualistic Hypothesis
Later Scientific Responses to the Individualistic Hypothesis
The Individualistic Hypothesis in the 21st Century
Gradient Analysis and the Vegetational Continuum
Early Historical Commentaries
Later Historical Responses

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Henry Allan Gleason by Malcolm Nicolson LAST REVIEWED: 16 August 2022 LAST MODIFIED: 11 January 2017 DOI: 10.1093/obo/9780199830060-0167

Up until the 1940s, plant ecology in Europe and North America was dominated by the community-unit theory—the concept that plants grow together in definite, repeating communities. These natural kinds of vegetation, generally termed “associations” or “formations,” were held to constitute the proper subject matter for ecological study, just as the plant species provided the proper object of study for taxonomic botany. The units were defined by the American ecologist George Nichols in his 1923 article “A Working Basis for the Ecological Classification of Plant Communities.” Thus, “the association may be described as a vegetation-unit characterized by its essentially constant physiognomy and by its essentially constant floristic composition” (p. 17). Between 1917 and 1945, only one American botanist dissented from the general consensus surrounding the community-unit theory—Henry Allan Gleason (b. 1882–d. 1975). In a key article, “The Individualistic Concept of the Plant Association” (1926), Gleason championed an alternative view, the “individualistic hypothesis,” arguing that the association was “not an organism, scarcely even a vegetation unit, but merely a coincidence” (p. 16). In his view, the phenomena of the plant community depended entirely upon the behavior of individual plants. Thus, associations or formations did not constitute basic units of which all vegetation was composed. The association was a classifier’s category, produced by the activity of classification rather than by the essential reality of vegetation, and it varied according to the priorities and interests of each classifier. Throughout the 1910s and early 1920s, Gleason was one of the most active field ecologists in North America. Moreover, the time of his maximum involvement in ecological research was also the period during which plant ecology became institutionalized as an academic specialty in the United States. Gleason was also an accomplished taxonomic botanist. In 1919 he was appointed assistant director of the New York Botanical Garden. (It should be noted that his work in taxonomic botany is not directly covered in this bibliography.) From the mid-1920s onward, his involvement in ecological research in the field diminished, as he established himself as one of America’s leading systematic botanists. However, several of his most important theoretical papers were produced in this latter period. After the Second World War, the broad unanimity as to the fundamental nature of vegetation began to break down. A number of younger American ecologists expressed dissatisfaction with the prevailing state of ecological science and called for a cautious reexamination of Gleason’s ideas. In the 1950s, a series of major field studies, notably by John Curtis and his students in Wisconsin, and by Robert Whittaker, who worked on the vegetation of the Great Smoky Mountains of the southeastern United States, revived the individualistic hypothesis. Gleason came to be regarded as one of the most important plant ecologists of the 20th century. However, his views have often been misrepresented or misunderstood, by both scientists and historians of science. This bibliographic survey seeks to document and clarify the development of his ecological ideas and to situate them in the context of plant ecological science in America in his time.

This section identifies the founding texts of American plant ecology, the publications by which the exemplar of ecological research that had been developed in Europe was transmitted to the universities of the Midwest. They form the beginning of a distinctive research tradition within which Gleason participated. Macmillan 1897 was the first large-scale ecological study published in the United States. Henry Chandler Cowles, at the University of Chicago, was one of the most influential American teachers of ecology. His first major paper ( Cowles 1899 ) is a comprehensive application of Warming’s work on the shoreline vegetation of Denmark to the sand dunes of Lake Michigan. Like Macmillan, Cowles emphasized that the relatively rapid topographical changes taking place within the dune systems make them favorable sites for vegetational research. In a general statement of the importance of topography in governing the character of vegetation ( Cowles 1901b ), he set out the principles of “physiographic ecology.” Cowles presented his system as “genetic and dynamic,” implying that it was based upon an understanding of vegetational succession and its relation to erosion and deposition. Cowles’s physiographic perspective conveyed a powerful sense of ubiquitous vegetational change, and of an underlying predictable regularity within that change. It promised a privileged insight into the history of vegetation. By walking through a dune system, from the newest dunes toward the mature ones, an observer could see laid out horizontally the developmental stages of the deciduous forest that was now established on the most stable, humus-covered dunes. Cowles 1901a is a forthright expression of monoclimax theory that all the vegetation of a given region is tending toward an ultimate common destiny, which, in the temperate United States, is mesophytic forest. Cowles’s work established the pride of place for successional studies within American ecology that they were to occupy until after World War II. Clements 1916 was the paradigmatic expression of Clements’s concept of the plant community. Clements held the formation to be a “complex organism,” alluding to the high degree of integration and orderly development he identified within it. Succession was “the basic organic process of vegetation, which results in the adult or final form of the complex organism” (p. 6). Retrogressive succession—vegetational changes that lead away from the climatic climax—was impossible. Gleason’s reading of Plant Succession ( Clements 1916 ) was the stimulus for his first theoretical paper ( Gleason 1917 , cited under Development of the Individualistic Hypothesis ). Plant Succession is a useful guide to the differences of opinion among early ecologists as to how to define the plant community, and it provides the background against which Gleason’s conception of the plant community should be understood. Charles Adams’s papers ( Adams 1902 , Adams 1905 ) combine floristic, ecological, and biogeographical interpretations and were an important influence on Gleason.

Adams, C. C. 1902. Southeastern United States as a center of geographical distribution of flora and fauna. Biological Bulletin 3:115–131.

DOI: 10.2307/1535493

Much of the biota of the central part of the northern United States is derived from the southeastern region. After the last Ice Age, southeastern species migrated north along three major routes: the Mississippi valley, the plain of the Atlantic seaboard, and the southern Appalachians. The distribution of biota should be interpreted “dynamically and genetically” in terms of the relationship between centers of origin and highways of dispersal.

Adams, C. C. 1905. The postglacial dispersal of the North American biota. Biological Bulletin 9:53–71.

DOI: 10.2307/1535802

The present distributions of biota are largely the product of past conditions. Climatic and habitat factors are important, but the character of a region’s flora is also determined by where its species originated. Analogy is made between the movements of flora northward into the land exposed by the retreating glaciers and vegetational successions observed in the present day. Successional processes may be ecologically similar in regions of different floral composition.

Clements, F. E. 1905. Research methods in ecology . Lincoln, NE: Univ. Publishing Company.

Clements sets out the key techniques and principles of field ecological research, including, in particular, the quadrat and transept methods. He also provides an elaborate terminology for the discipline, but not all his suggestions were adopted.

Clements, F. E. 1916. Plant succession: An analysis of the development of vegetation . Washington, DC: Carnegie Institution.

DOI: 10.5962/bhl.title.56234

Plant Succession provides a detailed interpretation of the vegetation of western North America, setting out the principles of Clements’s theory of vegetation and his research methods. The formation is held to be a “complex-organism,” characterized by orderly development and high degrees of integration. Succession is “the basic organic process of vegetation, which results in the adult or final form of the complex organism” (p. 6). Retrogressive succession is impossible.

Cowles, H. C. 1899. The ecological relations of the vegetation on the sand dunes of Lake Michigan. Botanical Gazette 27:95–117, 162–202, 281–308, 361–391.

Cowles’s interpretation of the sand dune vegetation is structured around the theme of topographic and vegetational development. While the topography influences the vegetation, the vegetation also modifies the topography. Cowles charts the historical stages of the sand features, from the dunes of the beach, through actively moving dunes, to mature, stationary dunes upon which a climax, mesophytic forest eventually establishes itself.

Cowles, H. C. 1901a. The influence of underlying rocks on the character of the vegetation. Bulletin of the American Bureau of Geography 2:163–176, 376–388.

While acknowledging that the physical and chemical nature of the underlying rock influences vegetation, Cowles asserts that physiography is more important than the underlying rock type. The flora of youthful limestone topography is more like the flora of a similar stage in sandstone than it is like that of mature limestone. The vegetation growing on clay hills today will eventually colonize granite hills, as erosion proceeds and humus accumulates.

Cowles, H. C. 1901b. The physiographic ecology of Chicago and vicinity: A study of the origin, development, and classification of plant communities. Botanical Gazette 31:73–108, 145–182.

Cowles subordinates every aspect of the habitat to a single variable—topography—which determines the water content of the soil and exposure to light and wind. As the general trend of physiographic change is toward the peneplain, so the general trend of vegetational change, in temperate regions, is toward mesophytic woodland. Cowles’s physiographic perspective conveyed a powerful sense of ubiquitous vegetational succession, and of a predictable regularity within that change.

Macmillan, C. 1897. Observations on the distribution of plants along shore at Lake of the Woods. Minnesota Botanical Studies 1:949–1023.

A detailed account of the “plant formations” of the dunes and shorelines of the lake. The comparatively rapid processes of vegetational change observable in bogs and dunes make those locations valuable for ecological research. Macmillan interprets the distribution of the various forms of vegetation in terms of the environmental and topographic conditions, emphasizing that many factors have to be taken into account to explain why a particular vegetation type grows where it does.

Nichols, G. 1923. A working basis for the ecological classification of plant communities. Ecology 4:11–23, 154–179.

A definitive exposition of the community-unit theory, as employed in ecological research in the United States. The concrete association—a particular stand of plants of “definite floristic composition” and “uniform physiognomy”—is distinguished from the abstract association, a higher category into which the individual stands may be classified. The abstract association is analogous to the taxonomic species. It is defined by floristic composition and physiognomy but, contra Clements, not by habitat.

Pound, R., and F. E. Clements. 1898. A method of determining the abundance of secondary species. Minnesota Botanical Studies 2:19–24.

Pound and Clements introduced the quadrat method into the American botanical literature, and thus provided Gleason (and many of his contemporaries) with an essential tool for ecological field research.

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Accounting for Ecological Capital
Adaptive Radiation
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Allelopathy
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individualistic hypothesis

Quick reference.

The view, first proposed by H. A. Gleason in 1917, that vegetation is continuously variable in response to a continuously varying environment. Thus, no two vegetation communities are identical. It implies also that vegetation cannot be classified, and that recognition of particular individual communities will be difficult (the problem arising because of the difficulty of defining boundaries). This viewpoint underlies one of the two polarized approaches to the description and analysis of vegetation communities that were much debated in the 1950s and 1960s. The individualistic hypothesis favours a continuum view of vegetation, for which ordination rather than classification methods are appropriate. Compare organismic.

From: individualistic hypothesis in A Dictionary of Plant Sciences »

Subjects: Science and technology — Life Sciences

The Role of Disturbance

Classic perspectives of succession.

Succession is one of the longest-studied ecological concepts. Henry Cowles was the first ecologist to thoroughly characterize successional patterns, which he did in his classic 1899 study of sand dunes along the shores of Lake Michigan (Cowles 1899). Cowles described the chronosequence of vegetation along sand dunes, moving from bare sand beach, to grasslands, to mature forests. A chronosequence is a “space-for-time” substitution, where ecologists can predict temporal patterns of vegetation based on a snapshot of an area gradient representing different ages of succession (Figure 1).

Figure 1: Chronosequences are often used to study succession (A) Typical chronosequence for sand dune succession. (B) Sleeping Bear Dunes National Lakeshore, MI showing successional chronosequence from bare sand to grassland to forest.

The concept of predictable change in vegetation time was next championed by Frederick Clements in the early 1900s. He proposed the concept of a climax state for communities, which represented the final, or permanent, end-stage of succession (Clements 1936). For Clements, climax communities were the assemblage of characteristic plants that define an ecosystem, such as tall grasses in a prairie, or mature trees in a forest. Clements held that, after a disturbance, any given ecosystem would eventually return to its characteristic assemblage of species. For example, if an oak-hickory forest had a severe forest fire which destroyed most of the trees, that forest system would eventually return to the climax community, defined by oak- and hickory-dominated species. Clements’s ideas of the extreme predictability of succession led him to propose a super-organism concept of succession, whereby all species in the climax community work together to maintain a stable composition (Figure 2). This idea, that an ecosystem could self-form, or self-renew into a stable climax community, became very popular in the 1920s.

Figure 2: Two contrasting views of succession (A) The super-organism concept, where groups of species are tightly associated, and are supplanted by other groups of tightly associated species. (B) The individualistic concept, where individual species independently respond to environmental conditions. Each curve on the graphs represents the abundance of a single species.

While the concept of a climax community is still viable today, the super-organism concept was opposed by another ecologist, Henry Gleason. Gleason argued that communities were individualistic; that is, communities were only the fortuitous assembly of species, and that there was no such thing as a climax state for ecosystems. Gleason recognized that the environment, and species’ movements, had an important role in regulating species assemblages, and that community changes were not nearly as predictable as Clements had proposed (Gleason 1926). While Gleason’s ideas were not well received by scientists in the 1920s, his recognition of the random aspects of community assembly are appreciated today by community ecologists interested in neutral models of biodiversity (e.g., Hubbell 2001).

Patterns and Mechanisms of Succession

Figure 3: Changes over time in total plant species richness over time at select sites on Mount Saint Helens, WA Plant reestablishment 15 years after the debris avalanche at Mount St. Helens, Washington. (Figure modified from Dale & Adams 2002) While ecologists today recognize that successional processes are less predictable than those proposed by Clements in the 1920s, several of his predicted patterns are generally considered to hold true for successional systems. For example, species diversity tends to increase with the successional age of an ecosystem. After the eruption of Mount St. Helens in the United States in 1980, ecologists monitoring the return of plant life to the mountain observed a steady increase in species diversity over time (Figure 3). Eugene Odum, an ecosystem ecologist, described several predictable differences between early and late successional systems. For example, early successional systems tend to have smaller plant biomass, shorter plant longevity, faster rates of soil nutrient consumption, a reduced role for decomposer organisms, more open and rapid biogeochemical cycling, higher rates of net primary productivity, lower stability, and lower diversity than late successional systems (Odum 1969). Similarly, Fakhri Bazzaz characterized early and late successional systems based on the physiology of plants associated with these stages. Early successional plants tend to have high rates of photosynthesis and respiration, high rates of resource uptake, and high light compensation points, whereas late successional plants often have opposite characteristics (Bazzaz 1979). It wasn’t until 1977 that ecologists actually proposed mechanisms by which communities might progress through predictable successional sequences. Facilitation is the most common mechanism proposed to explain succession. This occurs when one species, or a group of species, colonizes a disturbed area, and subsequently alters the environment of that area (by altering soil nutrients, light accessibility, or water availability), making it more habitable for later successional species (Connell & Slayter 1977). However, other possible mechanisms included tolerance, inhibition, and random colonization. One of the best examples of primary succession comes from studies by William Cooper, William Reiners, Terry Chapin, and others in Glacier Bay, Alaska (Cooper 1923, Reiners et al. 1971, Chapin et al. 1994). Since 1794, the glacier filling Glacier Bay has steadily been retreating (Figure 4a). Researchers have characterized primary succession in this system, where plant communities progress from pioneer species (i.e., early colonizing lichens, liverworts, and forbs) to creeping shrubs such as Dryas, to larger shrubs and trees such as alder, and finally to the climax spruce forest community over 1,500 years (e.g., see Chapin et al. 1994). Both facilitation and inhibition act as mechanisms regulating succession in this system (Figure 4b). For example, both Dryas and alders increase soil nitrogen, which increases the establishment and growth of spruce seedlings. However, both Dryas and alders produce leaf litter which can inhibit spruce germination and survival.

Figure 4: Succession after glacier retreat (A) Map of glacier retreat from 1794-1993 in Glacier Bay, AK. (B) Summary of facilitative and inhibitory effects of each successional stage of vegetation on spruce seedling growth. (Figure modified from Chapin et al. 1994)

A classic study of secondary succession was conducted by Catherine Keever (1950). In this study, Keever characterized succession in an old field after agricultural use had ceased. She observed a predictable shift in plant community composition following field abandonment, with horseweed ( Erigeron canadense ) dominating fields one year after abandonment, white aster ( Aster pilosis ) dominating in year two, and broomsedge ( Andropogon virginicus ) dominating in year three (Figure 5). She found that life history strategies of individual species, seed dispersal, allelopathy (biochemical production by a plant which alters growth and survival of other plants or itself), and competitive interactions among species, led to this predictable pattern of succession. Both Chapin’s and Keever’s studies clearly demonstrate that multiple mechanisms can operate during the process of succession.

Figure 5: Keever's observed pattern of succession in North Carolina agricultural old fields Figured modified from Keever 1950.

Recent Research on Succession

References and recommended reading.

Bazzaz, F. A. Physiological ecology of plant succession. Annual Review of Ecology and Systematics 10 , 351-371 (1979).

Chapin, F. S., Walker, L. R. et al. Mechanisms of primary succession following deglaciation at Glacier Bay, Alaska. Ecological Monographs 64 , 149-175 (1994).

Clements, F. E. Nature and structure of the climax. Journal of Ecology 24 , 252-84 (1936).

Connell, J. H. & Slayter, R. O. Mechanisms of succession in natural communities and their role in community stability and organization. American Naturalist 111 , 1119-1144 (1977).

Cooper, W. S. The recent ecological history of Glacier Bay, Alaska: the present vegetation cycle. Ecology 4, 223-246 (1923).

Cowles, H. C. The ecological relations of the vegetation on the sand dunes of Lake Michigan. Botanical Gazette 27 , 95-117, 167-202, 281-308, 361-391 (1899).

Gleason, H. A. The individualistic concept of the plant association. Bulletin of the Torrey Botanical Club 53 , 7-26 (1926).

Grime , J. P. Plant strategies and vegetation processes . New York, NY: John Wiley and Sons, 1979.

Horn, H. S. The ecology of secondary succession. Annual Review of Ecology and Systematics 5 , 25-37 (1974).

Hubbell, S. P. The Unified Neutral Theory of Biodiversity and Biogeography . Princeton, NJ: Princeton University Press, 2001.

Huston, M. & Smith, T. Plant succession- life history and competition. American Naturalist 130 ,168-198 (1987).

Keever, C. Causes of succession on old fields of the Piedmont, North Carolina. Ecological Monographs 20 ,229-250 (1950).

Koske, R. E., & Gemma, J. N. Mycorrhizae and succession in plantings of beachgrass in sand dunes. American Journal of Botany 84 , 118-130 (1997).

Odum, E. P. The Strategy of Ecosystem Development. Science 164 , 262-270 (1969).

Sakai, A. K., Allendorf, F. W. et al. The population biology of invasive species. Annual Review 32 , 305-332 (2001).

Tilman, G. D. The resource-ratio hypothesis of succession . American Naturalist 125 , 827 (1985).

Young, T. P., Petersen, D. A. et al. The ecology of restoration: historical links, emerging issues and unexplored realms. Ecology Letters 8 , 662-673 (2005).

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Biology Unit 1 hypothesis

Students also studied

DOI: 10.1111/j.1469-185X.1995.tb01069.x
Corpus ID: 6328280

H. A. GLEASON'S ‘INDIVIDUALISTIC CONCEPT’ AND THEORY OF ANIMAL COMMUNITIES: A CONTINUING CONTROVERSY

R. P. McIntosh
Published in Biological Reviews of The… 1 May 1995
Environmental Science, Biology

115 Citations

The myth of community as organism, neither superorganisms nor mere species aggregates: charles elton’s sociological analogies and his moderate holism about ecological communities, the history of early british and us-american ecology to 1950, what constitutes a community a co-occurrence exploration of the costa rican avifauna, the history of natural history and race: decolonizing human dimensions of ecology, are there general laws in ecology, community ecology: diversity and dynamics over time, are there general aws in ecology , ecology of coordinated stasis, long-term stasis in ecological assemblages: evidence from the fossil record*, 260 references, pluralism in ecology, mechanistic approaches to community ecology: a new reductionism, the community concept in marine zoology, with comments on continua and instability in some marine communities: a review, natural variability and the manifold mechanisms of ecological communities, littoral marine communities, the organismic community: resilience of an embattled ecological concept, what is a community, mechanistic approach to the structure of animal communities: anolis lizards and birds, some thoughts on the behaviour of ecologists, two decades of homage to santa rosalia: toward a general theory of diversity, related papers.

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Francis O'Leary's Working Title

Just another university of oregon sites site, the individualistic concept of the plant association. henry gleason (1926).

Throughout The Individualistic Concept of the Plant Association, Gleason makes several arguments as to what the particular issues are with a term as broad as “association”. The essay states that previous descriptions of plant associations are mistaken due to their attempts to fit within existing frameworks which were developed when less information was available, and that, instead, as new information becomes available, new frameworks should be developed. Due to the use of what Gleason might have called antiquated frameworks ecologists were making undue reaches as to the conclusions implied by their research. Gleason suggests a new model based upon the individual plant.

A plant association is defined by Gleason as “an area of vegetation, having a measurable extent, in which each of which there is a high degree of uniformity throughout, so that any two small portions of one of them look reasonably alike.” One of the main issues with this definition is that there may be a continuous stretch of grassland from Illinois to Nebraska, but the easternmost and westernmost portions have vast differences. Is it to be considered one association due to the continuous stretch of grassland, or two associations due to the multitude of smaller differences in species? If it is to be considered two associations, where should that “measurable extent” extend to if each square mile is almost indistinguishable from the next and it is only at great distances that a difference can be quantified? For another example, Gleason speaks of woodlands. Without human interaction, a woodland’s advance or retreat into or from a particular grassland would be so slow as to make it impossible to define clearly a time-boundary on when the association began or ended in a particular locale. Additionally, Gleason states, that, particularly in growth after a fire, an association may be so brief that there is never a period of equilibrium. Gleason then calls an association effectively a coincidence.

To back up this claim, Gleason explains, in simple terms, how plant life comes to be in an area; “if I viable seed migrates to a suitable environment, it germinates.” No matter how far it has traveled, whether on the wind, in an animal’s digestive system or on its fur, by stream, or any other manner, if a seed comes to rest someplace that can provide the right amount of sun, nutrients, and water, it will grow. The majority of seeds land relatively nearby the parent plant, and fewer and fewer do in concentric rings traveling outward from that plant. Thereby, Gleason contends, every plant germinates wherever it is able and grows in proximity to other vegetation with similar environmental needs. Plant associations as popularly defined by ecologists of the time were an attempt at ascribing monolithic order to a system containing billions and billions of free agents in the form of each individual plant attempting to grow and spread.

My personal thoughts on this writing are that it was an interesting idea and helped me to understand not only Gleason’s ideas but also other ecologists’ definition of a plant association. I largely agree with Gleason’s concept, however understand the utility of grouping vegetation into associations for the sake of study. Aside from all that, I thought Gleason’s clarity of voice made reading this essay easy and enjoyable.

1.2 The Process of Science

Learning objectives.

Identify the shared characteristics of the natural sciences
Understand the process of scientific inquiry
Compare inductive reasoning with deductive reasoning
Describe the goals of basic science and applied science

Like geology, physics, and chemistry, biology is a science that gathers knowledge about the natural world. Specifically, biology is the study of life. The discoveries of biology are made by a community of researchers who work individually and together using agreed-on methods. In this sense, biology, like all sciences is a social enterprise like politics or the arts. The methods of science include careful observation, record keeping, logical and mathematical reasoning, experimentation, and submitting conclusions to the scrutiny of others. Science also requires considerable imagination and creativity; a well-designed experiment is commonly described as elegant, or beautiful. Like politics, science has considerable practical implications and some science is dedicated to practical applications, such as the prevention of disease (see Figure 1.15 ). Other science proceeds largely motivated by curiosity. Whatever its goal, there is no doubt that science, including biology, has transformed human existence and will continue to do so.

The Nature of Science

Biology is a science, but what exactly is science? What does the study of biology share with other scientific disciplines? Science (from the Latin scientia, meaning "knowledge") can be defined as knowledge about the natural world.

Science is a very specific way of learning, or knowing, about the world. The history of the past 500 years demonstrates that science is a very powerful way of knowing about the world; it is largely responsible for the technological revolutions that have taken place during this time. There are however, areas of knowledge and human experience that the methods of science cannot be applied to. These include such things as answering purely moral questions, aesthetic questions, or what can be generally categorized as spiritual questions. Science cannot investigate these areas because they are outside the realm of material phenomena, the phenomena of matter and energy, and cannot be observed and measured.

The scientific method is a method of research with defined steps that include experiments and careful observation. The steps of the scientific method will be examined in detail later, but one of the most important aspects of this method is the testing of hypotheses. A hypothesis is a suggested explanation for an event, which can be tested. Hypotheses, or tentative explanations, are generally produced within the context of a scientific theory . A generally accepted scientific theory is thoroughly tested and confirmed explanation for a set of observations or phenomena. Scientific theory is the foundation of scientific knowledge. In addition, in many scientific disciplines (less so in biology) there are scientific laws , often expressed in mathematical formulas, which describe how elements of nature will behave under certain specific conditions. There is not an evolution of hypotheses through theories to laws as if they represented some increase in certainty about the world. Hypotheses are the day-to-day material that scientists work with and they are developed within the context of theories. Laws are concise descriptions of parts of the world that are amenable to formulaic or mathematical description.

Natural Sciences

What would you expect to see in a museum of natural sciences? Frogs? Plants? Dinosaur skeletons? Exhibits about how the brain functions? A planetarium? Gems and minerals? Or maybe all of the above? Science includes such diverse fields as astronomy, biology, computer sciences, geology, logic, physics, chemistry, and mathematics ( Figure 1.16 ). However, those fields of science related to the physical world and its phenomena and processes are considered natural sciences . Thus, a museum of natural sciences might contain any of the items listed above.

There is no complete agreement when it comes to defining what the natural sciences include. For some experts, the natural sciences are astronomy, biology, chemistry, earth science, and physics. Other scholars choose to divide natural sciences into life sciences , which study living things and include biology, and physical sciences , which study nonliving matter and include astronomy, physics, and chemistry. Some disciplines such as biophysics and biochemistry build on two sciences and are interdisciplinary.

Scientific Inquiry

One thing is common to all forms of science: an ultimate goal “to know.” Curiosity and inquiry are the driving forces for the development of science. Scientists seek to understand the world and the way it operates. Two methods of logical thinking are used: inductive reasoning and deductive reasoning.

Inductive reasoning is a form of logical thinking that uses related observations to arrive at a general conclusion. This type of reasoning is common in descriptive science. A life scientist such as a biologist makes observations and records them. These data can be qualitative (descriptive) or quantitative (consisting of numbers), and the raw data can be supplemented with drawings, pictures, photos, or videos. From many observations, the scientist can infer conclusions (inductions) based on evidence. Inductive reasoning involves formulating generalizations inferred from careful observation and the analysis of a large amount of data. Brain studies often work this way. Many brains are observed while people are doing a task. The part of the brain that lights up, indicating activity, is then demonstrated to be the part controlling the response to that task.

Deductive reasoning or deduction is the type of logic used in hypothesis-based science. In deductive reasoning, the pattern of thinking moves in the opposite direction as compared to inductive reasoning. Deductive reasoning is a form of logical thinking that uses a general principle or law to predict specific results. From those general principles, a scientist can deduce and predict the specific results that would be valid as long as the general principles are valid. For example, a prediction would be that if the climate is becoming warmer in a region, the distribution of plants and animals should change. Comparisons have been made between distributions in the past and the present, and the many changes that have been found are consistent with a warming climate. Finding the change in distribution is evidence that the climate change conclusion is a valid one.

Both types of logical thinking are related to the two main pathways of scientific study: descriptive science and hypothesis-based science. Descriptive (or discovery) science aims to observe, explore, and discover, while hypothesis-based science begins with a specific question or problem and a potential answer or solution that can be tested. The boundary between these two forms of study is often blurred, because most scientific endeavors combine both approaches. Observations lead to questions, questions lead to forming a hypothesis as a possible answer to those questions, and then the hypothesis is tested. Thus, descriptive science and hypothesis-based science are in continuous dialogue.

Hypothesis Testing

Biologists study the living world by posing questions about it and seeking science-based responses. This approach is common to other sciences as well and is often referred to as the scientific method. The scientific method was used even in ancient times, but it was first documented by England’s Sir Francis Bacon (1561–1626) ( Figure 1.17 ), who set up inductive methods for scientific inquiry. The scientific method is not exclusively used by biologists but can be applied to almost anything as a logical problem-solving method.

The scientific process typically starts with an observation (often a problem to be solved) that leads to a question. Let’s think about a simple problem that starts with an observation and apply the scientific method to solve the problem. One Monday morning, a student arrives at class and quickly discovers that the classroom is too warm. That is an observation that also describes a problem: the classroom is too warm. The student then asks a question: “Why is the classroom so warm?”

Recall that a hypothesis is a suggested explanation that can be tested. To solve a problem, several hypotheses may be proposed. For example, one hypothesis might be, “The classroom is warm because no one turned on the air conditioning.” But there could be other responses to the question, and therefore other hypotheses may be proposed. A second hypothesis might be, “The classroom is warm because there is a power failure, and so the air conditioning doesn’t work.”

Once a hypothesis has been selected, a prediction may be made. A prediction is similar to a hypothesis but it typically has the format “If . . . then . . . .” For example, the prediction for the first hypothesis might be, “ If the student turns on the air conditioning, then the classroom will no longer be too warm.”

A hypothesis must be testable to ensure that it is valid. For example, a hypothesis that depends on what a bear thinks is not testable, because it can never be known what a bear thinks. It should also be falsifiable , meaning that it can be disproven by experimental results. An example of an unfalsifiable hypothesis is “Botticelli’s Birth of Venus is beautiful.” There is no experiment that might show this statement to be false. To test a hypothesis, a researcher will conduct one or more experiments designed to eliminate one or more of the hypotheses. This is important. A hypothesis can be disproven, or eliminated, but it can never be proven. Science does not deal in proofs like mathematics. If an experiment fails to disprove a hypothesis, then we find support for that explanation, but this is not to say that down the road a better explanation will not be found, or a more carefully designed experiment will be found to falsify the hypothesis.

Each experiment will have one or more variables and one or more controls. A variable is any part of the experiment that can vary or change during the experiment. A control is a part of the experiment that does not change. Look for the variables and controls in the example that follows. As a simple example, an experiment might be conducted to test the hypothesis that phosphate limits the growth of algae in freshwater ponds. A series of artificial ponds are filled with water and half of them are treated by adding phosphate each week, while the other half are treated by adding a salt that is known not to be used by algae. The variable here is the phosphate (or lack of phosphate), the experimental or treatment cases are the ponds with added phosphate and the control ponds are those with something inert added, such as the salt. Just adding something is also a control against the possibility that adding extra matter to the pond has an effect. If the treated ponds show lesser growth of algae, then we have found support for our hypothesis. If they do not, then we reject our hypothesis. Be aware that rejecting one hypothesis does not determine whether or not the other hypotheses can be accepted; it simply eliminates one hypothesis that is not valid ( Figure 1.18 ). Using the scientific method, the hypotheses that are inconsistent with experimental data are rejected.

In recent years a new approach of testing hypotheses has developed as a result of an exponential growth of data deposited in various databases. Using computer algorithms and statistical analyses of data in databases, a new field of so-called "data research" (also referred to as "in silico" research) provides new methods of data analyses and their interpretation. This will increase the demand for specialists in both biology and computer science, a promising career opportunity.

Visual Connection

In the example below, the scientific method is used to solve an everyday problem. Which part in the example below is the hypothesis? Which is the prediction? Based on the results of the experiment, is the hypothesis supported? If it is not supported, propose some alternative hypotheses.

My toaster doesn’t toast my bread.
Why doesn’t my toaster work?
There is something wrong with the electrical outlet.
If something is wrong with the outlet, my coffeemaker also won’t work when plugged into it.
I plug my coffeemaker into the outlet.
My coffeemaker works.

In practice, the scientific method is not as rigid and structured as it might at first appear. Sometimes an experiment leads to conclusions that favor a change in approach; often, an experiment brings entirely new scientific questions to the puzzle. Many times, science does not operate in a linear fashion; instead, scientists continually draw inferences and make generalizations, finding patterns as their research proceeds. Scientific reasoning is more complex than the scientific method alone suggests.

Basic and Applied Science

The scientific community has been debating for the last few decades about the value of different types of science. Is it valuable to pursue science for the sake of simply gaining knowledge, or does scientific knowledge only have worth if we can apply it to solving a specific problem or bettering our lives? This question focuses on the differences between two types of science: basic science and applied science.

Basic science or “pure” science seeks to expand knowledge regardless of the short-term application of that knowledge. It is not focused on developing a product or a service of immediate public or commercial value. The immediate goal of basic science is knowledge for knowledge’s sake, though this does not mean that in the end it may not result in an application.

In contrast, applied science or “technology,” aims to use science to solve real-world problems, making it possible, for example, to improve a crop yield, find a cure for a particular disease, or save animals threatened by a natural disaster. In applied science, the problem is usually defined for the researcher.

Some individuals may perceive applied science as “useful” and basic science as “useless.” A question these people might pose to a scientist advocating knowledge acquisition would be, “What for?” A careful look at the history of science, however, reveals that basic knowledge has resulted in many remarkable applications of great value. Many scientists think that a basic understanding of science is necessary before an application is developed; therefore, applied science relies on the results generated through basic science. Other scientists think that it is time to move on from basic science and instead to find solutions to actual problems. Both approaches are valid. It is true that there are problems that demand immediate attention; however, few solutions would be found without the help of the knowledge generated through basic science.

One example of how basic and applied science can work together to solve practical problems occurred after the discovery of DNA structure led to an understanding of the molecular mechanisms governing DNA replication. Strands of DNA, unique in every human, are found in our cells, where they provide the instructions necessary for life. During DNA replication, new copies of DNA are made, shortly before a cell divides to form new cells. Understanding the mechanisms of DNA replication enabled scientists to develop laboratory techniques that are now used to identify genetic diseases, pinpoint individuals who were at a crime scene, and determine paternity. Without basic science, it is unlikely that applied science could exist.

Another example of the link between basic and applied research is the Human Genome Project, a study in which each human chromosome was analyzed and mapped to determine the precise sequence of DNA subunits and the exact location of each gene. (The gene is the basic unit of heredity represented by a specific DNA segment that codes for a functional molecule.) Other organisms have also been studied as part of this project to gain a better understanding of human chromosomes. The Human Genome Project ( Figure 1.19 ) relied on basic research carried out with non-human organisms and, later, with the human genome. An important end goal eventually became using the data for applied research seeking cures for genetically related diseases.

While research efforts in both basic science and applied science are usually carefully planned, it is important to note that some discoveries are made by serendipity, that is, by means of a fortunate accident or a lucky surprise. Penicillin was discovered when biologist Alexander Fleming accidentally left a petri dish of Staphylococcus bacteria open. An unwanted mold grew, killing the bacteria. The mold turned out to be Penicillium , and a new critically important antibiotic was discovered. In a similar manner, Percy Lavon Julian was an established medicinal chemist working on a way to mass produce compounds with which to manufacture important drugs. He was focused on using soybean oil in the production of progesterone (a hormone important in the menstrual cycle and pregnancy), but it wasn't until water accidentally leaked into a large soybean oil storage tank that he found his method. Immediately recognizing the resulting substance as stigmasterol, a primary ingredient in progesterone and similar drugs, he began the process of replicating and industrializing the process in a manner that has helped millions of people. Even in the highly organized world of science, luck—when combined with an observant, curious mind focused on the types of reasoning discussed above—can lead to unexpected breakthroughs.

Reporting Scientific Work

Whether scientific research is basic science or applied science, scientists must share their findings for other researchers to expand and build upon their discoveries. Communication and collaboration within and between sub disciplines of science are key to the advancement of knowledge in science. For this reason, an important aspect of a scientist’s work is disseminating results and communicating with peers. Scientists can share results by presenting them at a scientific meeting or conference, but this approach can reach only the limited few who are present. Instead, most scientists present their results in peer-reviewed articles that are published in scientific journals. Peer-reviewed articles are scientific papers that are reviewed, usually anonymously by a scientist’s colleagues, or peers. These colleagues are qualified individuals, often experts in the same research area, who judge whether or not the scientist’s work is suitable for publication. The process of peer review helps to ensure that the research described in a scientific paper or grant proposal is original, significant, logical, and thorough. Grant proposals, which are requests for research funding, are also subject to peer review. Scientists publish their work so other scientists can reproduce their experiments under similar or different conditions to expand on the findings.

There are many journals and the popular press that do not use a peer-review system. A large number of online open-access journals, journals with articles available without cost, are now available many of which use rigorous peer-review systems, but some of which do not. Results of any studies published in these forums without peer review are not reliable and should not form the basis for other scientific work. In one exception, journals may allow a researcher to cite a personal communication from another researcher about unpublished results with the cited author’s permission.

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Hypothesis n., plural: hypotheses [/haɪˈpɑːθəsɪs/] Definition: Testable scientific prediction

Table of Contents

What Is Hypothesis?

A scientific hypothesis is a foundational element of the scientific method . It’s a testable statement proposing a potential explanation for natural phenomena. The term hypothesis means “little theory” . A hypothesis is a short statement that can be tested and gives a possible reason for a phenomenon or a possible link between two variables . In the setting of scientific research, a hypothesis is a tentative explanation or statement that can be proven wrong and is used to guide experiments and empirical research.

It is an important part of the scientific method because it gives a basis for planning tests, gathering data, and judging evidence to see if it is true and could help us understand how natural things work. Several hypotheses can be tested in the real world, and the results of careful and systematic observation and analysis can be used to support, reject, or improve them.

Researchers and scientists often use the word hypothesis to refer to this educated guess . These hypotheses are firmly established based on scientific principles and the rigorous testing of new technology and experiments .

For example, in astrophysics, the Big Bang Theory is a working hypothesis that explains the origins of the universe and considers it as a natural phenomenon. It is among the most prominent scientific hypotheses in the field.

“The scientific method: steps, terms, and examples” by Scishow:

Biology definition: A hypothesis  is a supposition or tentative explanation for (a group of) phenomena, (a set of) facts, or a scientific inquiry that may be tested, verified or answered by further investigation or methodological experiment. It is like a scientific guess . It’s an idea or prediction that scientists make before they do experiments. They use it to guess what might happen and then test it to see if they were right. It’s like a smart guess that helps them learn new things. A scientific hypothesis that has been verified through scientific experiment and research may well be considered a scientific theory .

Etymology: The word “hypothesis” comes from the Greek word “hupothesis,” which means “a basis” or “a supposition.” It combines “hupo” (under) and “thesis” (placing). Synonym: proposition; assumption; conjecture; postulate Compare:   theory See also: null hypothesis

Characteristics Of Hypothesis

A useful hypothesis must have the following qualities:

It should never be written as a question.
You should be able to test it in the real world to see if it’s right or wrong.
It needs to be clear and exact.
It should list the factors that will be used to figure out the relationship.
It should only talk about one thing. You can make a theory in either a descriptive or form of relationship.
It shouldn’t go against any natural rule that everyone knows is true. Verification will be done well with the tools and methods that are available.
It should be written in as simple a way as possible so that everyone can understand it.
It must explain what happened to make an answer necessary.
It should be testable in a fair amount of time.
It shouldn’t say different things.

Sources Of Hypothesis

Sources of hypothesis are:

Patterns of similarity between the phenomenon under investigation and existing hypotheses.
Insights derived from prior research, concurrent observations, and insights from opposing perspectives.
The formulations are derived from accepted scientific theories and proposed by researchers.
In research, it’s essential to consider hypothesis as different subject areas may require various hypotheses (plural form of hypothesis). Researchers also establish a significance level to determine the strength of evidence supporting a hypothesis.
Individual cognitive processes also contribute to the formation of hypotheses.

One hypothesis is a tentative explanation for an observation or phenomenon. It is based on prior knowledge and understanding of the world, and it can be tested by gathering and analyzing data. Observed facts are the data that are collected to test a hypothesis. They can support or refute the hypothesis.

For example, the hypothesis that “eating more fruits and vegetables will improve your health” can be tested by gathering data on the health of people who eat different amounts of fruits and vegetables. If the people who eat more fruits and vegetables are healthier than those who eat less fruits and vegetables, then the hypothesis is supported.

Hypotheses are essential for scientific inquiry. They help scientists to focus their research, to design experiments, and to interpret their results. They are also essential for the development of scientific theories.

Types Of Hypothesis

In research, you typically encounter two types of hypothesis: the alternative hypothesis (which proposes a relationship between variables) and the null hypothesis (which suggests no relationship).

Simple Hypothesis

It illustrates the association between one dependent variable and one independent variable. For instance, if you consume more vegetables, you will lose weight more quickly. Here, increasing vegetable consumption is the independent variable, while weight loss is the dependent variable.

Complex Hypothesis

It exhibits the relationship between at least two dependent variables and at least two independent variables. Eating more vegetables and fruits results in weight loss, radiant skin, and a decreased risk of numerous diseases, including heart disease.

Directional Hypothesis

It shows that a researcher wants to reach a certain goal. The way the factors are related can also tell us about their nature. For example, four-year-old children who eat well over a time of five years have a higher IQ than children who don’t eat well. This shows what happened and how it happened.

Non-directional Hypothesis

When there is no theory involved, it is used. It is a statement that there is a connection between two variables, but it doesn’t say what that relationship is or which way it goes.

Null Hypothesis

It says something that goes against the theory. It’s a statement that says something is not true, and there is no link between the independent and dependent factors. “H 0 ” represents the null hypothesis.

Associative and Causal Hypothesis

When a change in one variable causes a change in the other variable, this is called the associative hypothesis . The causal hypothesis, on the other hand, says that there is a cause-and-effect relationship between two or more factors.

Examples Of Hypothesis

Examples of simple hypotheses:

Students who consume breakfast before taking a math test will have a better overall performance than students who do not consume breakfast.
Students who experience test anxiety before an English examination will get lower scores than students who do not experience test anxiety.
Motorists who talk on the phone while driving will be more likely to make errors on a driving course than those who do not talk on the phone, is a statement that suggests that drivers who talk on the phone while driving are more likely to make mistakes.

Examples of a complex hypothesis:

Individuals who consume a lot of sugar and don’t get much exercise are at an increased risk of developing depression.
Younger people who are routinely exposed to green, outdoor areas have better subjective well-being than older adults who have limited exposure to green spaces, according to a new study.
Increased levels of air pollution led to higher rates of respiratory illnesses, which in turn resulted in increased costs for healthcare for the affected communities.

Examples of Directional Hypothesis:

The crop yield will go up a lot if the amount of fertilizer is increased.
Patients who have surgery and are exposed to more stress will need more time to get better.
Increasing the frequency of brand advertising on social media will lead to a significant increase in brand awareness among the target audience.

Examples of Non-Directional Hypothesis (or Two-Tailed Hypothesis):

The test scores of two groups of students are very different from each other.
There is a link between gender and being happy at work.
There is a correlation between the amount of caffeine an individual consumes and the speed with which they react.

Examples of a null hypothesis:

Children who receive a new reading intervention will have scores that are different than students who do not receive the intervention.
The results of a memory recall test will not reveal any significant gap in performance between children and adults.
There is not a significant relationship between the number of hours spent playing video games and academic performance.

Examples of Associative Hypothesis:

There is a link between how many hours you spend studying and how well you do in school.
Drinking sugary drinks is bad for your health as a whole.
There is an association between socioeconomic status and access to quality healthcare services in urban neighborhoods.

Functions Of Hypothesis

The research issue can be understood better with the help of a hypothesis, which is why developing one is crucial. The following are some of the specific roles that a hypothesis plays: (Rashid, Apr 20, 2022)

A hypothesis gives a study a point of concentration. It enlightens us as to the specific characteristics of a study subject we need to look into.
It instructs us on what data to acquire as well as what data we should not collect, giving the study a focal point .
The development of a hypothesis improves objectivity since it enables the establishment of a focal point.
A hypothesis makes it possible for us to contribute to the development of the theory. Because of this, we are in a position to definitively determine what is true and what is untrue .

How will Hypothesis help in the Scientific Method?

The scientific method begins with observation and inquiry about the natural world when formulating research questions. Researchers can refine their observations and queries into specific, testable research questions with the aid of hypothesis. They provide an investigation with a focused starting point.
Hypothesis generate specific predictions regarding the expected outcomes of experiments or observations. These forecasts are founded on the researcher’s current knowledge of the subject. They elucidate what researchers anticipate observing if the hypothesis is true.
Hypothesis direct the design of experiments and data collection techniques. Researchers can use them to determine which variables to measure or manipulate, which data to obtain, and how to conduct systematic and controlled research.
Following the formulation of a hypothesis and the design of an experiment, researchers collect data through observation, measurement, or experimentation. The collected data is used to verify the hypothesis’s predictions.
Hypothesis establish the criteria for evaluating experiment results. The observed data are compared to the predictions generated by the hypothesis. This analysis helps determine whether empirical evidence supports or refutes the hypothesis.
The results of experiments or observations are used to derive conclusions regarding the hypothesis. If the data support the predictions, then the hypothesis is supported. If this is not the case, the hypothesis may be revised or rejected, leading to the formulation of new queries and hypothesis.
The scientific approach is iterative, resulting in new hypothesis and research issues from previous trials. This cycle of hypothesis generation, testing, and refining drives scientific progress.

Importance Of Hypothesis

Hypothesis are testable statements that enable scientists to determine if their predictions are accurate. This assessment is essential to the scientific method, which is based on empirical evidence.
Hypothesis serve as the foundation for designing experiments or data collection techniques. They can be used by researchers to develop protocols and procedures that will produce meaningful results.
Hypothesis hold scientists accountable for their assertions. They establish expectations for what the research should reveal and enable others to assess the validity of the findings.
Hypothesis aid in identifying the most important variables of a study. The variables can then be measured, manipulated, or analyzed to determine their relationships.
Hypothesis assist researchers in allocating their resources efficiently. They ensure that time, money, and effort are spent investigating specific concerns, as opposed to exploring random concepts.
Testing hypothesis contribute to the scientific body of knowledge. Whether or not a hypothesis is supported, the results contribute to our understanding of a phenomenon.
Hypothesis can result in the creation of theories. When supported by substantive evidence, hypothesis can serve as the foundation for larger theoretical frameworks that explain complex phenomena.
Beyond scientific research, hypothesis play a role in the solution of problems in a variety of domains. They enable professionals to make educated assumptions about the causes of problems and to devise solutions.

Research Hypotheses: Did you know that a hypothesis refers to an educated guess or prediction about the outcome of a research study?

It’s like a roadmap guiding researchers towards their destination of knowledge. Just like a compass points north, a well-crafted hypothesis points the way to valuable discoveries in the world of science and inquiry.

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What Is a Biological Individual?

First Online: 23 July 2019

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Jan Baedke 3

Part of the book series: Fascinating Life Sciences ((FLS))

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This paper addresses the concept of individual and its role in biological theory and practice. The ability to identify individuals, paradigmatically organisms, is central not only to address them as coherent units of variation or selection. The criteria chosen to define individuality directly affect which entities we consider worth investigating, which kind of methods and models we chose, which properties (like agency) these units possibly can have, and what kind of questions we ask about them. In this paper, first, the history of the concept of biological individuality as well as underlying criteria such as indivisibility are described. Second, it is shown that in the light of rapid developments in high-throughput technologies and novel organism-centered views of evolution in the so-called extended evolutionary synthesis (including evo-devo, epigenetics, and niche construction theory), answering the old question what a biological individual is becomes more important than ever before. This is the case as it turns out to be increasingly difficult to identify individuals, as organisms come to be understood as deeply embedded in their environment. Sometimes, they are even part of other organisms (in holobionts). The answers given to these challenges have not only theoretical and methodological consequences, such as for choosing model organisms, but also affect human life in a number of ways.

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Baedke, J. (2019). What Is a Biological Individual?. In: Martín-Durán, J., Vellutini, B. (eds) Old Questions and Young Approaches to Animal Evolution. Fascinating Life Sciences. Springer, Cham. https://doi.org/10.1007/978-3-030-18202-1_13

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Biological Individuals

Biological individuals are an important feature of the world we live in. To better understand this we can start with a focal question: what are biological individuals? As simple as that sounds, it quickly leads to puzzling but illuminating complexities and variations in the biological world. To address these, it helps to articulate the larger conceptual space surrounding the focal question. A distinction between evolutionary and physiological individuals is also useful in thinking about biological individuals, as is attention to the kinds of groups, such as superorganisms and species, that have sometimes been thought of as biological individuals. More fully understanding the conceptual space that biological individuals occupy also involves considering a range of other concepts, such as life, reproduction, and agency. There has been a focus in some recent discussions by both philosophers and biologists on how evolutionary individuals are created and regulated, as well as continuing work on the evolution of individuality.

1. The Focal Question: What are Biological Individuals?

2. some complexities: a humungous fungus and coral reefs, 3.1 beyond organisms: microbialism, eliminativism, and holobionts, 3.2 distinctions: the evolutionary and the physiological, 3.3 conceptual space and pluralism, 4. structuring conceptual space beyond pluralism, 5. groups as evolutionary individuals: superorganisms, trait groups, species, clades, 6.1 physiological individuals as living agents, 6.2 reproduction, life cycles, and lineages, 6.3 autonomous agency, 7. locating biological individuals in conceptual space, 8. regulating evolutionary individuals, 9. the evolution of biological individuality, other internet resources, related entries.

The biological world contains an incredibly diverse variety of individuals. At the ground level of common sense, there are alligators, ants, beetles, marmots, moles, mushrooms, ostriches, roses, trees, and whales. At this ground level, biological individuals are physically-bounded, relatively well-integrated, autonomous agents, the ones listed as being amongst those that can be readily detected with the senses. Extending the reach of common sense through magnification allows flagella-propelled protists, tRNA molecules, prions, and bacteria of many kinds to be seen or inferred. At larger or collective scales, there are herds of zebras, sweeping and astonishing coral reefs, algae blooms, biofilms made up of many different species, and even fungus complexes several hectares in area and with masses greater than that of an elephant.

What we will call the Focal Question —what are biological individuals?—can be paraphrased in a number of ways:

What constitutes being a biological individual?
What makes something a biological individual?
What is the nature of the category biological individual ?
What is the best explicative definition of the term “biological individual”?

In the rapidly expanding literature on biological individuals (cf. Hull 1992 with Guay & Pradeu 2016a, 2016b, and Lidgard & Nyhart 2017b), such questions take biological individual as a general category that may subsume several kinds of biological individual (e.g., evolutionary, developmental, genetic, metabolic; cf. Okasha forthcoming).

The psychologist Hermann Ebbinghaus’s famous quip that “psychology has a long past, but only a short history” (1908: 1, Die Psychologie hat eine lange Vergangenheit, doch nur eine kurze Geschichte ) might well be adapted to remind us that answers to the Focal Question have a long past, one stretching back to at least the late eighteenth-century with the emergence of the life sciences. In their collection of essays Biological Individuality , the historians Scott Lidgard and Lynne Nyhart reviewed the literature of the past two hundred years to compile a list of twenty three criteria used to define or characterize “ individual or its contained subset organism ”, noting that while

the terms are not equivalent, they have been used interchangeably in many publications, precluding a simple separation here. (2017a: 18)

Addressing the Focal Question thus calls for sensitivity to this tendency in the long past.

As Derek Skillings says, the “traditional target of accounts of biological individuality is the organism” (2016: 880), a tradition reinforced in some influential contemporary discussions that simply identify biological individuals with organisms (Queller & Strassmann 2009, Clarke 2013; see section 8 below). The present review follows Lidgard and Nyhart and others (Dupré & O’Malley 2009; Nicholson 2014; Pradeu 2016a, 2016b) in taking biological individual to name a superordinate category whose nature and relation to the category organism is complex and worthy of exploration. Some commentators (e.g., Okasha forthcoming) may be skeptical that there is any such superordinate category, suspecting instead that several distinct categories, including organism, are typically lumped together in unclear and misleading ways as ‘biological individuals’. By contrast, here we view answers to the Focal Question as appropriate attempts to explore and clarify various relationships between distinct sorts of biological individuals.

Philosophers of biology typically understand biological individuals to be distinct from other kinds of entities in the biosciences, such as properties, processes, and events; however, the development of a process-focused ontology by John Dupré and colleagues has challenged this (Dupré 2012, Nicholson 2018, Nicholson & Dupré 2018, Meincke 2019; Kearney and Rieppel 2023; see Morgan 2022 for a critique). Biological individuals have three-dimensional spatial boundaries, endure for some period of time, are composed of physical matter, bear properties, and participate in processes and events. Biological processes (such as photosynthesis) and biological events (such as speciation) lack such a suite of features. Although philosophers have explored the question of what makes anything an individual of any kind (e.g., Strawson 1959; van Inwagen 1990; Chauvier 2016; French 2014, 2016; Lowe 2016; Wiggins 2016), such questions are bracketed off here in order to concentrate on biological individuals (cf. Love & Brigandt 2017).

To provide a sense of the complexities that an answer to the Focal Question must address, consider, below, two examples that take us from the ground level of common sense with which this review began to the intimate interplay between empirical data gathered by biologists and the conceptual clarification provided by philosophers that is a hallmark of thinking about biological individuals. The philosopher Jack Wilson (1999: 23–25) introduced the first of these examples into discussions of biological individuals, while the physiologist Scott Turner (2000: ch.2) introduced the second; both were then drawn upon in an early, sustained discussion of the nature of organisms that takes up some of the complexities raised by such examples—a discussion that pre-dates the consolidation of the contemporary literature around the term “biological individuals” (R.A. Wilson 2005: ch.3–4).

In the early 1990s, a team of biologists reported in the journal Nature that they had found high levels of genetic identity in samples of a species of fungus ( Armillaris bulbosa ), which had taken over a large geographic region in Michigan’s Upper Peninsula. They used this data to make a case for viewing these samples as constituting parts of one gigantic biological individual with an estimated biomass of more than ten tons and an estimated age exceeding 1500 years. They concluded that “members of the fungal kingdom should now be recognized as among the oldest and largest organisms on earth” (Smith, Bruhn, & Anderson 1992: 431). Some scientists have questioned whether this final claim about the organismal status of the humungous fungus is warranted, and some have argued it is mistaken to say the gigantic fungus constitutes a single biological individual. Since then, other scientists have recognized even larger funguses as biological individuals (Schmitt & Tatum 2008).

How does one judge such claims and disputes? Minimally, more empirical information about the example is needed. Is the fungus a continuous biological structure? Does it have a determinate growth pattern? Can it reproduce? But this empirical information alone doesn’t settle the matter. One must also draw on antecedent concepts of organism and biological individual. The empirical information, in turn, also allows one to fine-tune, amend, or challenge those antecedent concepts, better so than would common sense reflection alone. For example, if the humungous fungus is not an organism but some other sort of biological individual, which empirical considerations motivate this distinction?

Consider a more elaborately described example (Turner 2000: ch.2; see also Skillings 2016: 877–879). Coral reefs are spectacular and beautiful parts of the living world, despite rapidly becoming a thing of the past due to the climate changes associated with global warming. At least at the ground level of common sense, they are often thought of as consisting of two chief components. The first are accretions of calcite deposits. The second are the small animals, polyps, which produce and grow on the deposits. (Coral polyps belong to the same Linnaean class as sea anemones, and to the same Linnaean phylum as jellyfish.) The polyps are indisputably biological individuals. But further, conservation biologists also often describe the coral reefs themselves, consisting of the polyps and the deposits considered together, as living things that can grow and die.

The reefs are at least biological individuals, typically being thought of as ecosystems; formal methods already exist for modeling them as such (e.g., Huneman 2014). And taking seriously their life, growth and death leads to the question of whether they too might be organisms: to a first approximation, metabolically-circumscribed entities that are relatively well-integrated and function as a whole. The dependence relations between the reefs and the polyps does not rule this out, since such dependence is common in organisms. Human beings depend on internal bacteria that outnumber our own cells by about ten to one, and yet they are organisms (Ackerman 2012). Similarly, the polyps that reefs depend on are themselves dependent on single-celled algae, commonly referred to as zooxanthellae , for the glucose that provides the energy necessary for polyp respiration, which in turn drives the process of calcification. Moreover, it is the zooxanthellae that supply the pigments that give living corals their spectacular colors; when zooxanthellae are absent or diminished, this signals a problem for the long-term survival of a coral reef. Neither are the zooxanthellae free of dependence. By infecting the polyps they gain a feeding den crucial to their survival.

Further reflection along these lines may suggest that an integrated causal network of dependence relations is a mark of being an organism or biological individual; “causal integration, cohesion, collaboration, or agency of parts” is the criterion on Lidgard and Nyhart’s (2017a) list of criteria that they found most often cited in the literature they reviewed. If that were so, then the coral reef may come to be viewed as a better exemplar of either than are the polyps and zooxanthellae, as the reef enjoys a kind or degree of complex, functional integrity that polyps and zooxanthellae arguably lack when considered singly (see also Combes 2001). Alternatively, perhaps the reef should be thought of as some other kind of biological individual, such as an ecosystem, that contains several distinct organisms, the polyps and the zooxanthellae, as proper parts.

Again, knowing what to say about the striking claim that the polyp-zooxanthellae-calcite deposit complex is an organism turns in part on the empirical facts, but on more than just those. Polyps, zooxanthellae and whole reef complexes do not wear placards that state which is an example of an organism, and whether all three should be viewed as biological individuals of some kind or other (and which kind). The interplay between our conceptions and empirical complexities both allows those conceptions to be unpacked and informs how they might be regimented to better capture nuances of the biological world inaccessible to commonsense reflection alone.

This interplay has recently involved philosophers and biologists attending more squarely to the microbial world (O’Malley, Simpson, & Roger 2013; O’Malley 2014), recognizing the various tight integrative and collaborative relations between what prima facie are distinct biological individuals (Dupré & O’Malley 2009, Ereshefsky & Pedroso 2015), and trying to make sense of the diversity one finds in the processes of reproduction, metabolism, and development (Godfrey-Smith 2016b, Griesemer 2016). The next section provides an introductory survey of this interplay via discussion of three subsidiary questions.

3. Conceptual Space, Distinctions, and Beyond Organisms

Responses to the Focal Question have advanced discussion of at least three closely related subsidiary questions:

Beyond Organisms: In what ways does the traditional focus on organisms hinder us in thinking about biological individuals?
Distinctions: What are the most useful distinctions between various kinds of biological individuals?
Conceptual Space: What is the most informative way to articulate the conceptual space surrounding the concept of biological individuals?

The first of these questions anchors our discussion in the short history of thinking about biological individuals while acknowledging the long past of the Focal Question.

Scientists themselves—following common sense—have been drawn first and foremost to organisms when beginning their theorizing about biological individuals. For example, consider John Maynard Smith and Eörs Szathmáry’s The Major Transitions of Life (1995), a wide-ranging book on the origins and evolution of life that has stimulated much work on the evolution of individuality (Buss 1987) and the Darwinian dynamics (Michod 1999) that governs emerging kinds of biological entities (see Herron 2021 for recent discussion and section 9 below). The book opens with a simple point about the living world and a characterization of the book’s chief theme:

Living organisms are highly complex, and are composed of parts that function to ensure the survival and reproduction of the whole. This book is about how and why this complexity has increased in the course of evolution. The increase has been neither universal nor inevitable. (Maynard Smith & Szathmáry 1995: 3)

Here organisms or biological individuals are viewed as exemplars of complex living things composed of many parts, and their complexity is taken to have increased—albeit unevenly and contingently—through evolution by natural selection.

Likewise, an early collection of essays on evolutionary developmental biology (“evo-devo”) by Gerd Müller and Stuart Newman (2003) focuses on how organismal form originated and on the evolutionary, developmental, and ecological processes shaping it over generations. The essays in that volume concentrate on the relationships between basic body plans of organisms over phylogenetic time, rather than the evolution of individuality as such, and do not take up The Focal Question about biological individuals at all. But like that of Maynard Smith and Szathmáry, the project of exploring these relationships is naturally expressed in terms of the concept of an organism.

This should occasion no surprise, since, as section 1 indicated, organisms have historically been regarded as prominent examples of biological individuals and organism and biological individual have often been used interchangeably. But the short quotation drawn from Maynard Smith and Szathmáry also helps to explain why simply equating biological individuals with organisms would be a mistake. The parts that compose organisms in all their complexity are, often enough, themselves biological individuals. Even if some of those parts are also organisms (e.g., the microbes that live on and in macrobes), many are not. Precisely the same is true of the populations and lineages that individual organisms in turn constitute. These may occasionally be organisms (e.g., eusocial insect colonies as “superorganisms”), but typically populations and lineages are biological individuals that are not organisms. If either this internal compositional complexity to organisms or their formation into populations and lineages are necessary features of organisms (which many philosophers and biologists at least tend to think they are; see Lidgard & Nyhart 2017a: 18–23), then this would prove a stronger conclusion: given that there are organisms, there must be some biological individuals that are not organisms.

So one way in which the traditional focus on organisms can hinder us in thinking about biological individuals is if, by equating the two, there is too little attention focused on biological individuals that are not organisms. But hindrance here could take a different form, as some have argued. One might think that a focus on organisms, particularly those identified at the ground level of common sense, commits not just this kind of error of omission, but also proves positively misleading about what biological individuals are. Consider two positions that challenge the privileging of organisms in discussions of The Focal Question:

Microbialism : Understanding the living world requires focusing on collaborations between macrobes and a variety of microbes (e.g., viruses, prions, plasmids, symbionts), taking seriously the idea that the biological individuals identified at the ground level of common sense constitute a small part of that world (Dupré & O’Malley 2007, 2009).
Eliminativism: Far from being paradigmatic biological individuals, organisms may be marginal or unusual special cases of biological individuals and should be eliminated from our ontology (Haber 2013, Okasha 2011).

Microbialism has been part and parcel of Dupré and O’Malley’s plaint against the macrobist bias in the philosophy of biology and the positive case they have made for the significance of the microbial world for reconceptualizing biological individuals (O’Malley 2014, 2015; O’Malley, Simpson, & Roger 2013; Dupré 2010). One direction that this has been taken is Dupré’s (2012) promiscuous individualism (for the relationship between this view and processualism, see Morgan 2022: 616–617).

Promiscuous individualism is not simply the view that there are many legitimate ways to classify the world into biological individuals. It is also the corresponding ontological view that such legitimation is provided by there being multiple biological individuals there to classify. To illustrate this view, consider lichens, which are typically regarded as what have been called corporate organisms (R.A. Wilson 2005: 80–84), in this case made up of a fungus and either a cyanobacterium or some other photosynthesizing agent, such as green algae. Challenging the view that there is just one biological individual (the lichen) or two (the fungus and the cyanobacterium), an advocate of promiscuous individualism can readily make the case that there are three biological individuals (the lichen, the fungus, and the cyanobacterium), pointing to the different purposes and goals one might have in opting for any of the numerical counts here.

Given that it is a population of millions of cyanobacteria inhabiting any given fungus that jointly compose a lichen, and that there are multiple ways to draw the boundary between individual fungi of a given species (Molter 2017; cf. Rayner 1997), note how rampant promiscuity can run here. Dupré himself holds that populations, including multispecies populations such as those found in microbial biofilms, can themselves be both biological individuals and organisms (2012: 89, 175–176, 194, 203). He also says that “[w]hether a group of microbes is a closely connected ecological community or an organism may be a matter of biological judgment” (2012: 153). Promiscuous individualism thus implies that there are many, many different numbers of individuals present in this paradigm case. It seems even to suggest that whether there are any biological individuals at all is “a matter of biological judgment”, rather than something determined by the biological facts.

The emphasis on collaborations between living things in Microbialism can undermine the focus on organisms without entering (at least directly) into these deep metaphysical waters. That emphasis can also motivate Eliminativism. One way it can do so is by embracing the idea that it is not organisms but holobionts that are really paradigmatic biological individuals. Introduced by Lynn Margulis (1990) to refer to cases where there was intergenerational, inherited symbiosis, such as that of the eukaryotic cell and of Buchnera -aphid symbiosis), “holobiont” made its way into discussions of coral reefs and a wider range of examples early in the twenty-first century by loosening Margulis’s concept (see Suárez 2020 for discussion). In the literature on biological individuals, a holobiont is, at least roughly, “the multicellular eukaryote plus its colonies of symbionts” (Gilbert & Tauber 2016: 842).

This concept has been attractive to some scientists (e.g., Zilber-Rosenberg & Rosenberg 2008; Bordenstein & Theis 2015; Bosch & Miller 2016) but critiqued by others (Moran and Sloan 2015 and Douglas & Werren 2016) while also sparking ongoing philosophical work (Theis et al. 2016, Booth 2014, Doolittle & Booth 2017). For example, a special issue of the journal Biology & Philosophy on biological individuality (volume 31, issue 6) contains papers that focus on the significance of the holobiont for immunology (Chiu & Eberl 2016; Gilbert & Tauber 2016) and for the evolution of individuality and its major transitions (Queller & Strassmann 2016, Skillings 2016; cf. Bourrat & Griffiths 2018). In an interesting recent paper, Lloyd and Wade (2019) argue that the critics of the holobiont concept typically rely on gene-centric and conflict-focused research on multispecies interactions, suggesting that one can pursue a different set of research questions within community genetics that pave the way for an articulation of the co-evolutionary roles for holobionts. As part of their case, they introduce the distinction between euholobionts – “genuinely genetically integrated, coadapted communities of obligately mutualistic organisms” which are evolutionary and physiological individuals – and demiholobionts , such as the squid-vibrio complex, that are forms of mutualism with asymmetrical fitness and so adaptational relationships (Lloyd and Wade 2019: 152). They argue that by viewing these cases as “lying on a continuum of fitness interactions and partner fidelities” (p.166), together with their advertised multilevel research strategy, we arrive at a model of mutualism and holobionts that better matches reality.

Like the concept of an organism that it putatively supplements or supplants, that of the holobiont encompasses a huge diversity of entities. These include macro-organisms and the microbial endosymbionts living within their cells (such as Chlamydia and other obligate parasites); those that live beyond their cells but in close symbiotic relations (such as cyanobacteria); and the multispecies microbiota that inhabit the human intestine (Booth 2014). There are challenges in how to delineate individual holobionts that, as we will see in the next section, may be met by embracing particular physiological criteria for individuation (Pradeu 2012). Yet those challenges have suggested to some that the take-away lesson from reflection on holobionts is that emphasis should be placed not on another kind of individual, a holobiont, but instead on the process of holobiosis (Doolittle & Booth 2017). Others have recently defended a cluster of contrasting views (Suárez and Stencel 2020; Suárez 2020). One is that biological individuals can be thought of as ecosystems, an idea that draws upon a notion of “weak individuals” defined in terms of levels of interaction (Huneman 2021); another is that holobionts are both biological individuals and ecological communities or ecosystems, which draws on the proposal that biological individuality needs to be given a part-dependent characterization that recognizes the perspective-dependence of questions about the ontology of holobionts (Suárez and Stencel 2020). And finally there is the idea that the hologenome should be conceptualized in terms of stability of traits, rather than fitness alignment (Suárez 2020). These ideas enrich discussions of the concept of holobionts, and whether that concept will live up to its still-early promise of revolutionizing thinking about biological individuals is likely to remain a topic of lively discussion in the immediate future.

Consider now our second subsidiary question, Distinctions: what are the most useful distinctions between the various kinds of biological individuals that exist? The most commonly recognized distinction here is that between evolutionary and physiological (or metabolic ) individuals (Pradeu 2016a, 2016b), with a corresponding discussion of the roles of evolution and metabolism in thinking about biological individuals (see Clarke 2020 and O’Malley 2020 for opposing views).

Prominent in contemporary thinking about evolutionary individuals is the work of Peter Godfrey-Smith on what he calls Darwinian individuals . On the view of evolution and natural selection he defends in Darwinian Populations and Natural Selection (2009), what evolves are “Darwinian populations”, collections of things in which at least three conditions hold: there is variation in the traits had by things in the collection, those traits are heritable within the collection, and some variants of the traits confer reproductive advantage on the things that bear them. In such a Darwinian population, the members are Darwinian individuals, which are both bearers and active reproducers of heritable traits (see Godfrey-Smith 2013: 19–20).

Godfrey-Smith’s approach to evolutionary individuals is intended to contrast with the earlier replicator-based views developed by Richard Dawkins and others. Replicator views have been central to discussions of the levels and units of selection (Godfrey-Smith 2015; Sober & Wilson 1994, 1998; Okasha 2006), and derivatively so to views of biological individuals. Here genes are paradigmatic replicators, being housed in interactors , such as organisms, and it is the survival of these replicators that matters in evolution. The replicator framework emphasizes the importance for natural selection of high-fidelity copying across generations. By contrast, what matters for natural selection in Godfrey-Smith’s view is the establishment of parent-offspring lineages that feature heritability, as well as the variety of forms that reproduction can take in the establishment and stabilization of those lineages.

This shift from replication to the process of reproduction in accounts of biological individuals has a longer history, particularly amongst those sensitive to the relationships between evolution and development. For example, James Griesemer (2000) has argued that biological reproduction involves fission and fusion requiring what he calls progeneration , a process that creates new entities through material overlap , and that that process is a crucial feature of how living agents evolve. Section 6 takes up this issue in more detail in discussing reproduction, life cycles, and lineages.

Whichever way evolutionary individuals are conceptualized, they do not exhaust the realm of biological individuals any more than do organisms. The general point here is that although evolution is foundational when thinking about interactors and Darwinian individuals, it does not play this role for all kinds of biological individual, as Godfrey-Smith himself recognizes. Indeed, Godfrey-Smith (2013) strikingly (and controversially) proposes that even some organisms , understood from a metabolic point of view, are not Darwinian individuals at all. These are a subset of corporate organisms, multi-species organisms formed through symbiotic relationships between members of different species. Here Godfrey-Smith posits the Hawaiian bobtail squid ( Euprymna scolopes) and the Vibrio bacteria they contain as an example (see also Nyholm & McFall-Ngai 2004; Bouchard 2010). Since the squid-Vibrio corporate organism does not itself form the right kinds of parent-offspring lineages it is not a Darwinian individual, differing in this respect with other often-discussed corporate organisms, such as aphid- Buchnera complexes (Andersson 2000):

Figure 1: Godfrey-Smith’s Different Biological Individuals. (Copied from Figure 4 of Godfrey-Smith 2013.) [An extended description of figure 1 is in the supplement.]

Whatever one says about the intricacies of such examples, in addition to individuals delineated by evolutionary criteria there are also what Thomas Pradeu calls physiological individuals. These are biological individuals individuated by appeal to criteria such as having a metabolism and being governed by internal control mechanisms of various kinds. For Pradeu, each physiological individual is “a functionally integrated and cohesive metabolic whole, made of interdependent and interconnected parts” (Pradeu 2016b: 807; see also Godfrey-Smith 2009: 71).

As Pradeu notes (2016b: 799–802), there is a long tradition in the physiological sciences of addressing the Focal Question by asking what it is that makes for unity of functioning in biological individuals:

to ask how distinct and heterogeneous components interact and constitute a cohesive whole, functioning collectively as a regulated unit that persists through time. (2016b: 800)

Although there is typically a nod paid to physiological individuals in early influential discussions of biological individuals in the short history of the topic (e.g., Sober 1991, Hull 1992, Dawkins 1989: ch.13), the bulk of this literature has focused until very recently on evolutionary individuals. Pradeu’s reminder of the long past of the Focal Question, and the prominence of physiological individuals in it, is a welcome redress to the resulting skew of attention.

In addition to this general point, Pradeu has also defended the view that an organism is a particular kind of physiological individual, being

a functionally integrated whole composed of heterogeneous components that are locally interconnected by strong biochemical interactions and controlled by constant systemic immune interactions of a constant average intensity. (Pradeu 2012: 244)

Here Pradeu builds on a particular view of immunology developed in his The Limits of the Self that moves beyond the theory associated with Frank Burnet, the self-nonself theory. In its place, Pradeu offers a general account of immunogenicity that applies across a wide range of phlya, ignoring the exogenous or endogenous origin of antigens in favor of a criterion that emphasizes immune-tolerance and acceptance.

Pradeu takes the boundary established and maintained by the immune system as the boundary of the organism. On Pradeu’s view, organisms are inherently heterogeneous, given the collaborative nature of the microbial and macrobial worlds articulated in Microbialism. To put it slightly differently, the true organisms delineated by Pradeu’s immunity criterion are holobionts constituted by a macrobial organism and all and only those microbes at least tolerated by its immune system. This criterion provides a way to individuate organisms as holobionts , and the resulting view constitutes one way to constructively respond to the challenges of Microbialism and Eliminativism. Whether holobionts are best thought of as organisms or evolutionary individuals at all (Skillings 2016), or whether Pradeu’s view in particular can resolve the putative “tension in seeing symbionts as both organisms themselves and also parts of larger organisms” (Godfrey-Smith 2016c: 782), remain live issues.

So minimally there are evolutionary individuals and there are physiological individuals, and organisms are typically thought of as exemplars of (but not strictly identical to) both. Godfrey-Smith’s articulation of evolutionary individuals as Darwinian individuals has structured much recent and ongoing discussion, and Pradeu’s emphasis on physiological individuals and his appeal to immunology as a source for ideas about organisms and biological individuals more generally has garnered recent attention. These responses to Distinctions also facilitate rich responses to our remaining subsidiary question, Conceptual Space: What is the most informative way to articulate the conceptual space surrounding the concept of biological individuals?

Recognizing the distinction between evolutionary and physiological individuals commits one to a minimal form of pluralism about what populates that conceptual space. But there are also more radical forms that pluralism about biological individuals has taken in the literature. Section 3.1 indicated that the emphasis on the collaborative nature of the interactions between biological individuals in Microbialism motivates Dupré’s promiscuous individualism, a position that invites a very liberal form of pluralism that makes biological individuality seem, at least partly, a function of our epistemic, practical, and other proclivities, rather than of just the structure of the biological world itself.

Here Dupré can be understood as following the general intuition that if some kind K seems too diverse to characterize, it should be split into diverse sub-kinds, with each of those characterized. In early philosophical work (J. Wilson 1999, 2000) also drew on this intuition, where K = biological individual, moving beyond that broad concept to characterize genetic , functional , developmental, and evolutionary individuals, a position more recently dubbed “kind pluralism” and defended by appeal to explanatory power and projectability (DiFrisco 2019). Famously, the botanist John Harper invoked pluralism, where K = plant, by introducing the more particular kinds ramet and genet to replace talk of individuals. A ramet is what might be readily identified as an individual plant; a genet is a collection of ramets that propagate, as is often the case, through the clonal growth of a particular ramet (Harper 1977). How many plants there are, in many cases, depends on whether ramets or genets are meant. For example, while each of the trees in an aspen grove that forms clonally is a ramet, collectively they typically form a single genet. A pluralist might prefer a description cast in terms of ramets and genets over any attempt to answer the question of how many plants or individuals, per se, there are in this case.

Pluralism about biological individuals has also been motivated by the general idea that particular epistemic practices , rather than or additional to high-level biological theory, should drive one’s ontological commitments (Kovaka 2015, Chen 2016, Love 2018; for interplay of theory and experimental practice in this connection, see Fagan 2016). Just as practices of the individuation of species might vary with the differential practices of (say) ciliatologists and ornithologists, so too might the very individuative criteria for being a (relevant) biological individual differ according to the varying epistemic practices across the biological sciences. How radical the resulting form of pluralism is will depend in part on how fine-grained one’s view of the relevant practices is and the expanse of the range of those practices. For example, are all of the practices in developmental biology clustered, or are distinctions to be drawn between those relevant to the experimental investigation of growth and those relevant to homology? Are we to include among biological individuals, as Roberta Millstein (2018) does when discussing the land community , very large systems studied in ecology, which are made up of diverse organisms, other living things, and non-living things such as soil (see also Eliot 2011)? Answers to such questions will influence whether the plausibility of what Alan Love calls strong individuality pluralism , the view that “for a given situation, individuality can be modeled correctly in more than one way” (2018: 187). Kaiser and Trappes (2021) have recently argued from this kind of “practice turn” perspective, to motivate questions about uniqueness and temporality that further broaden the problem agenda of appeals to biological individuality.

So far some of the pluralistic directions that discussions of Distinctions and Conceptual Space have taken in the literature have been outlined, leading to a conceptual landscape populated by a plethora of adjectivally-modified kinds of individuals: evolutionary, physiological, developmental, functional, genetic, etc.. Although simply equating biological individuals with organisms would be a mistake, some biologists (e.g., Pepper & Herron 2008; cf. Jagers op Akkerhuis 2010) have explored the idea that a more nuanced appeal to organisms can provide some informative structure to this landscape. Noting that

amongst biologists, the question of what constitutes an individual is usually identical with the question of what constitutes an individual organism. (Pepper & Herron 2008: 622)

Pepper and Herron pose the question of whether any given biological individual is an organism, a part of an organism, or a group of organisms. Consider then a framework that holds that biological individuals include exactly:

organisms (such as wasps and whales)
some parts of organisms (such as placentas and plasmids) and
some groups of organisms (such as zebra lineages and colonies of bacteria).

Figure 2 depicts this framework visually.

a diagram: link to extended description below

Figure 2: A Framework for Structuring Conceptual Space. [An extended description of figure 2 is in the supplement.]

These three sub-categories of biological individual need not be mutually exclusive when considering any particular individual. For example, a given bacterium, such as an individual Buchnera bacterium, may both be an organism itself and be part of a corporate organism, such as the human whose gut it is integral to (Andersson 2000). Likewise, some groups, such as the colonies of eusocial insects sometimes called “superorganisms”, or highly integrated multispecies communities, may be true organisms. This kind of view may also capture what truth lies behind proposals to extend the term organism both to some parts and some groups of organisms (e.g., Queller 1997; Okasha 2011): parts of organisms (such as symbiotic gut bacteria), as well as groups of organisms (such as colonies of ants or bees), are really organisms as well.

Directly relevant to the Focal Question is that this framework invites a more systematic treatment of the relationship between each of the primary kinds of biological individuals—evolutionary and physiological individuals—and other key features typically appealed to in characterizing them, including growth, reproduction, lineages, cohesion, metabolism, and control. Sections 6 and 7 will elaborate the initial visual summary offered by Figure 2 in ways that further fill out the conceptual space occupied by biological individuals. But first Section 5 attends to the right-hand side of Figure 2 by providing a brief overview of the idea of groups as biological individuals.

As the discussion of evolutionary individuals in section 3 indicated, responses to the question of whether natural selection has created groups that are themselves biological individuals has been important to the history of the Focal Question. Groups here might range from temporary dyads of individuals, such as two crickets sharing a ride on a leaf (Sober & Wilson 1998), through to higher-level taxonomic groups whose members are largely separated in space and time, such as planktotrophic mollusks (Jablonski 1986, 1987). One fundamental distinction that emerged with the revival of group selection, largely through the work of David Sloan Wilson (1975, 1977, 1980, 1983) and Elliott Sober (D.S. Wilson & Sober 1989; Sober & Wilson 1994, 1998), is between two sorts of groups: superorganisms and trait groups.

The term superorganism was introduced by the entomologist William Morton Wheeler in his 1920 essay “Termitodoxa, or Biology and Society”, although he had talked of ant colonies as organisms as early as his 1911 essay “The Ant-Colony as an Organism”. Paradigm examples of superorganisms are colonies of social insects, e.g., Hymenoptera such as ants, wasps, and bees, together with the taxonomically distinct termites, which are typically viewed as a special kind of biological individual arising from the specific genetics and reproductive division of labor in those colonies.

Trait group was introduced by D.S. Wilson, by contrast, specifically to name a type of group that he thought was pervasive in nature, one that could be a unit of selection just as individual organisms were. The intuitive idea behind a trait group is that populations can feature evolutionarily relevant structure wherein organisms belonging to one part of the population are subject to causal influences on fitness that do not extend to the population as a whole. A population of such structured demes would then function as a metapopulation, with natural selection operating between the trait groups that make up that metapopulation. The individuals in a trait group could thus be seen as evolutionary individuals, being the agents for evolutionary change over time.

A common two-pronged response to this distinction (e.g., Sterelny 1996) has been to concede the reality of superorganismic group selection (but underscore its rarity) and argue that instances of trait group selection are better described as cases of genic or individual selection relativized to a particular environment, where part of that environment is composed of other individual organisms (see also Okasha 2006, 2018). In effect, this is to allow for superorganisms as a special kind of biological individual, but to reject a more expansive conception of evolutionary individual at the group level. On this view, eusocial insects may be evolutionary (and even physiological) individuals, but trait groups are neither.

A distinct pathway taken by appeals to group selection has focused on species and clade selection, particularly in work by paleobiologists and paleontologists (Grantham 1995; see also Doolittle 2017). Clades are monophyletic groups of organisms or species, groups defined by an ancestor and all and only its descendants. Steven Stanley and Stephen Jay Gould have been two of the most prominent defenders of the idea that there are large-scale patterns of evolutionary change that are due to species or clade selection, and both have done so in part by explicitly developing an extended analogy between individual organisms and species (e.g., Stanley 1979: 189; Gould 2002: 703–744). Amongst putative examples of clade selection are the evolution of planktotrophic mollusks in the late Cretaceous, being selected for greater geographic dispersal and so longevity (Jablonski 1986, 1987), the evolution of larger body size in males, selected via population density and geographic range (Brown & Maurer 1987, 1989), and the evolution of flowering plants, selected via vector-mediated pollen dispersal (Stanley 1981: 90–91).

There is a similar caution in discussions of species or clades as evolutionary or physiological individuals as there is with trait groups. One of the chief threads to the debate over species and clade selection also parallels that over trait group selection: are species or clades themselves really the agents of selection, the units that are being selected, or do they simply tag along for the ride, with selection operating exclusively on organisms and genes? Elisabeth Vrba (1984, 1989; Vrba & Gould 1986), for example, has distinguished between species sorting and species selection , arguing that while a sorting of species may be the product of evolution by natural selection (see Barker & Wilson 2010), this outcome is typically brought about not by species selection but by individual selection. On this view, species or clades may be a product of natural selection, and so in some sense evolutionary individuals, but they are not themselves agents in the process of natural selection. Rather, they are epiphenomena of that process, lacking the kind of agency that full-blown evolutionary individuals have.

The much-discussed claim that species are individuals (Ghiselin 1974; Hull 1976, 1978), which developed as part of a response to the perceived failure of essentialism about species (Sober 1980; Okasha 2002; Barker 2013), might be viewed in this same light. The species-as-individuals thesis reflects the way in which species were treated within systematics and evolutionary biology not as kinds but instead as spatiotemporally restricted lineages , with individual organisms as their physical parts (Ereshefsky 1992a; R.A. Wilson 1999b). The species-as-individuals thesis was originally presented and seen as making a radical break with previous views of the ontological status of species, as it implied that biologists and philosophers alike had misidentified the basic ontological category to which species belonged. But over time, both as its proponents have clarified what the thesis implied (e.g., gravitating to talk of historical entities rather than individuals) and as more sophisticated options for defenders of the view that species are kinds were developed (e.g., Boyd 1999, Griffiths 1999, R.A. Wilson 1999a), this radical edge to the thesis has diminished. A now widely accepted insight clarified in the process is that in the case of many species, organisms belong to them (as parts or members) by virtue of their interactions and their extrinsic rather than intrinsic properties (Barker 2010; cf. Devitt 2008). Whether this combats (or instead exemplifies) what the historian James Elwick has recently called “resilient essentialisms” (Elwick 2017; cf. Hull 1965) remains contentious.

Finally here, Mariscal and Doolittle (2020) have recently suggested that all of life, i.e., the Last Universal Common Ancestor and all of its descendants, is a biological individual in the sense in which Ghiselin and Hull argued that species were (see Reydon 2021 for some scepticism about both claims). They take life to be “a monophyletic clade that originated with a last universal common ancestor, and includes all of its descendants” (2020: abstract). Complementing this is their adaption of Ereshefsky’s (1992b) eliminative pluralism about living things as a kind, arguing for eliminativism about living things as a natural kind (cf. Barker 2019).

6. From Physiological to Evolutionary Individuals: Life, Reproduction, and Agency

Section 3 indicated that John Maynard Smith and Eörs Szathmáry drew explicitly on the concept of living organisms in characterizing the chief theme of their influential work on the major transitions in the history of life. However, reflection on organisms as living agents generally has been backgrounded in work concentrating on evolutionary individuals. This is perhaps for the obvious reason that many evolutionary individuals—including genes, lineages, and clades—are not themselves living things. Yet physiological individuals are paradigms of living agents and a more complete sense of the conceptual space that biological individuals occupy calls for some discussion of life, including the roles that an appeal to life cycles and agency play in characterizing physiological individuals.

One approach here would be to attempt to define life, or living agent, or to provide necessary and sufficient conditions for these (Maynard Smith & Szathmáry 1995: 17–18; Cleland 2012). A recurrent property referenced in such definitions is that of having a metabolism , which involves both an anabolic dimension in the breakdown of chemical molecules to produce energy and a catabolic dimension in intracellular synthesis of those compounds (Pradeu 2016b: 801). But there are other properties that living agents have, some presupposed by that of having a metabolism, others existing independently. These include what might be thought of as structural properties—such as having heterogeneous and specialized parts, including a variety of internal mechanisms, and containing diverse organic molecules, including nucleic acids and proteins—as well as functional or dispositional properties—such as the capacity for growth or development, reproduction, and self-repair.

Cells, organs, and perhaps bodily systems, such as the respiratory system or the digestive system, are physiological individuals that have most if not all of these properties that characterize living agents. As physiological individuals, organisms also share these properties, but are distinguished by one or more further characteristics, such as possessing an immune system (as Pradeu emphasizes) or having a life cycle , one that is typically demarcated through reproduction, which is the focus of section 6.2 below.

Conceiving of physiological individuals as living agents, and supposing that all organisms are living agents but that there may be both parts and groups of organisms that are not, allows us to extend the visual summary introduced in Figure 2 . Figure 3 depicts organisms as living agents but also contains regions for organs such as hearts and other constituent parts of organisms as living agents, as well as groups that may be living agents but not organisms (e.g., perhaps a coral reef).

Figure 3: Living Things as Biological Individuals. [An extended description of figure 3 is in the supplement.]

One feature of organismic, physiological individuals that partially distinguishes them amongst living things is that they have life cycles that allow them to form reproductive lineages of a certain kind. The importance of life cycles for evolutionary change has been recognized both in the replicator-based view of evolutionary individuals (Dawkins 1989: ch.13) and in reproductively-centered accounts of Darwinian individuals (Godfrey-Smith 2009, 2016a). And the close relationship between being an individual organism and having a life cycle is widely accepted, being manifested in an extreme form by Griffiths and Gray’s (1994) identification of biological individuals with their life cycles within developmental systems theory.

Put most generally, a life cycle is an intergenerationally replicable series of events or stages through which a living thing passes (Bonner 1993). These events or stages constitute a cycle in that they begin and end with the same event, such as the formation of a fertilized egg in sexually reproducing individuals, or the creation of a fissioned cell in clonally reproducing individuals. Development is the global name for the processes that causally mediate between these events or stages in a life cycle, with reproduction marking the transition to the creation of a new individual, the offspring of one or more parents. Although Richard Dawkins’s suspicion

that the essential, defining feature of an individual organism is that it is a unit that begins and ends with a single-celled bottleneck (1989: 264)

has proven hyperbolic, the more cautious view that the “two phenomena, bottlenecked life cycles and discrete organisms, go hand in hand” (1989: 264) expresses a view that has been widely endorsed.

It has long been recognized that some biological individuals, such as flukes, have life cycles that take them literally through one or more hosts, and that many insects undergo significant metamorphic changes in bodily form through their life cycle. But such sophistications to life cycles are only the tip of the iceberg here. While the stages themselves often form standard sequences within particular species, there can be tremendous variation across species and phyla in what a given individual’s life cycle consists in, as others have emphasized (Buss 1987), including in recent discussions of complex life cycles (Godfrey-Smith 2016b, 2016d; Griesemer 2016; Herron 2016; O’Malley 2016; cf. Gerber 2018).

In the life cycles that are most immediately familiar, processes that mark the end of one life cycle and the beginning of another of the same kind of individual—processes such as material bottlenecking, sexual reproduction, and multiplication—temporally coalesce. In the life cycles of other individuals, such as ferns and scyphozoan jellyfish, these processes are sometimes dispersed, function differently, or are absent (Godfrey-Smith 2016a, 2016b). Such cases call for a corresponding sophistication of accounts of reproduction and, as James Griesemer says, these complexities in life cycles may

complicate relations between processes of development and reproduction to such an extent that even the meaning of ‘organism’ begins to break down. (Griesemer 2016: 804)

Maureen O’Malley (2016) has drawn attention to other cases that pose more radical challenges to the standard ways of thinking of life cycles themselves. An example is the asexually reproducing multicellular protist Volvox carteri (green algae), whose “sexual phase of the life cycle is nonreproductive because there is no multiplication” (O’Malley 2016: 838). This kind of sexual recombination occurring between members of asexually reproducing generations takes on a striking form in ciliates, such as Tetrahymena , whose micronucleus provides germ-line isolation. Whether O’Malley’s concept of multigenerational individuals can be squared with extensions of standard views of reproduction and life cycles remains subject to further exploration.

Although there is a relationship between having a life cycle and reproducing, simply reproducing is not the distinctive feature here, as a number of authors have recognized (Griesemer 2014, Godfrey-Smith 2013, O’Malley 2016, R.A. Wilson 2005: 59-62). Organisms and perhaps other biological individuals typically reproduce through material overlap (Griesemer 2000), or via bottlenecks requiring material minimalization and mark the transition between generations (Godfrey-Smith 2009: ch.5). These kinds of constraints on biological reproduction go hand in hand with growth and development as part of the intergenerational life cycle of biological individuals. Intergenerational life cycles, in turn, make it possible for biological individuals to form reproductive lineages of living things. Reproduction structures not only such lineages, but also the lineages of non-living biological individuals, whether they be smaller than the individuals they are parts of (such as genes), or groups (such as populations) that feature centrally in discussions of evolutionary individuals.

Despite the fact that reproduction has sometimes been conceptualized as part of an individual’s life cycle, the general role of reproduction in intergenerational life cycles requires more careful articulation. For there are many species in which only a small minority of individuals actually get to reproduce, with reproductive skew being a widespread feature. All of these biological individuals, however much or little they reproduce, still possess a life cycle. Note that even the capacity to reproduce is not a universal feature of life cycles. This is not only because the capacity itself may not be replicated, but also because there are biological individuals designed by natural selection to be non-reproductive, with sterile castes in eusocial insects being perhaps the best-known example.

In such species, a few individuals (e.g., queens) do most if not all of the direct reproductive labor, and many others are rendered reproductively sterile throughout all or much of their life (e.g., worker castes). So there are reasons to include neither reproduction nor the capacity to reproduce as part of the generic life cycle of biological individuals. What is true, however, is that all organisms have life cycles that allow them to form reproductive lineages. They do so sometimes through the reproductive activity of members of the lineage to which they belong, even if not every member of that lineage reproduces or even can reproduce. Like viruses, individual members of sterile castes of insects rely on the reproductive machinery of others in order for descendant members of those castes to be reproduced in future generations.

This is an example of what Godfrey-Smith (2009: ch.5) calls scaffolded reproducers , “entities which get reproduced as part of the reproduction of some larger unit” and whose “reproduction is dependent on an elaborate scaffolding of some kind that is external to them” (2009: 88). These contrast with what he calls simple reproducers , a paradigm of which is a bacterial cell, being “the lowest-level entities that can reproduce largely ‘under their own steam’” (2009: 88). Both simple and scaffolded reproducers can be parts of what Godfrey-Smith calls collective reproducers , which are

reproducing entities with parts that themselves have the capacity to reproduce … largely through their own [the parts’] resources rather than through the coordinated activity of the whole. (2009: 87)

Both groups and multicellular organisms exemplify collective reproduction, and Godfrey-Smith’s discussion of the continuous dimensional space that characterizes collective reproducers, and Darwinian individuals more generally, has been influential, and is summarily depicted in Figure 4 below.

Figure 4: Godfrey-Smith’s Dimensional Space for Collective Reproduction. (From Figure 5.1 in Godfrey-Smith 2009.) [An extended description of figure 4 is in the supplement.]

That all physiological individuals have some kind of autonomous agency is widely recognized and is the intuitive basis for the early systematic formal theorization of biological autonomy undertaken on autopoetic systems by Maturana and Varela (1980) and more recently by Moreno and Mossio (2015). Although such views are typically cast in terms of biological systems rather than individuals, they view the kind of unity of purpose that characterizes both physiological and evolutionary individuals as arising from more general principles governing biological organization, and that organization is important to biological individuality.

Physiological individuals such as organisms, however, are not simply biological systems but living agents that have a life of their own . They are able to exercise some sort of special degree of control over their whole selves and subsequently are relatively free with respect to other things, including other agents and environments. This might be expressed in terms of both the individual’s relative autonomy from its external environment and its control over the activity of its components or internal parts (R.A. Wilson 2005: 62–65). Organisms in particular have a distinctive kind of agency because of the integrity with which such autonomy and control imbues them. For Moreno and Mossio (2015: ch.6), developmental functions and constraints play an especially important role in establishing this kind of organismic autonomy.

The idea of biological individuals having a locus of control in ways that neither non-living things nor obligately-dependent living things (such as organs) have is key here. Pradeu’s (2012) view of immunological control as marking the boundary of the biological individual is one way of specifying this idea, as is Godfrey-Smith’s continuous dimension of integration , which summarizes features such as

the extent of division of labor, the mutual dependence (loss of autonomy) of parts, and the maintenance of a boundary between a collective and what is outside of it. (2009: 93)

The high level of functional integration or cohesion possessed by parts of individuals imbues the whole organisms they constitute with both capacities to act and largely shared fates to which those capacities contribute (Collier 2004; Okasha 2011: 59; Sober 1991: 291). In some sense, this is why any organism has a life to lead , rather than simply being alive.

This appeal to autonomous agency has a long history in thinking about what is distinctive about the biological world, particularly when the focus has been on physiological individuals. For example, in the first volume of his Principles of Biology (1866), Herbert Spencer argued at length that the capacity of a biological individual to

continuously adjust its internal relations to external relations, so as to maintain the equilibrium of its functions (1866: 207, our emphasis)

is one of the key features that sets it apart as biological. Likewise when Julian Huxley later proposed three conditions of what he called minimal organismality , one of these concerned integration of internal functions and a second concerned independence from external forces (Huxley 1912: 28). Like Spencer, Huxley saw these internal and external matters as causally linked within individuals, and as together achieving equilibria in distinctive ways. Huxley thought this was due especially to the parts of biological individuals being both more heterogeneous and functionally integrated with each other than is seen in the non-biological context external to such individuals. Two contemporary cousins of this idea in the literature focused on evolutionary individuals will be the focus of section 8 below.

Denis Walsh has articulated a general organism-centred perspective on evolution and the biological sciences that emphasizes teleological agency (Walsh 2015). Walsh dubs this perspective as “methodological vitalism” (Walsh 2018) and the “agential perspective” (Walsh and Rupik 2023) and has argued that it constitutes an alternative to the view of evolution associated with the Modern Synthesis (see Buskell and Currie 2017 for discussion). Walsh and colleagues give important roles to autonomy in the conception of organismal agency, with Fulda recently arguing that the notion of autonomous agency can be used to provide a general criterion for biological individuality (Fulda 2023), one in which paradigm cases of biological individuality, like multicellular organisms, display strong autonomous agency, while what he calls “problematic cases” (Fulda 2023, section 4.4) display weak agential dependence.

An interesting, relatively recent question is why the use of cognitive metaphors in describing biological agency is widespread, if not ubiquitous (R.A. Wilson 2005: ch.4). Explorations of this question have involved some interesting integrative thinking across the philosophy of biology, cognitive science, and the philosophy of economics (Godfrey-Smith 2009: 142–145; Dennett 2011; Nicholson 2018; Okasha 2018). Four responses to this question give some idea of the diverse literatures relevant to answering it.

One early hypothesis (R.A. Wilson: 2005: 74–79) is that the function of these metaphors is to crystallize agency , bringing about a focus on the causal agency of biological individuals by assimilating them to our paradigm of agents, human agents. This crystallization thesis forms part of Wilson’s tripartite view of organismic living agents (R.A. Wilson 2005: ch.3) that draws on the homeostatic property cluster view of natural kinds (Boyd 1999, R.A. Wilson, Barker, & Brigandt 2007). A second view is that the cognitive metaphor applies when behaviors and processes are goal-directed, behavior is flexible, and there is exhibition of adaptation, and the metaphor earns it keep through the parallels between rational choice theory and evolutionary theorizing (Okasha 2018). Okasha is concerned to articulate the scope and limits of the cognitive metaphor in evolutionary biology, taking organisms as his paradigm agents. A third view is that the use of psychological predication of the activities of cells, neurons, and bodily systems is not metaphorical but should be taken literally (Figdor 2018). Figdor’s literalism is a response to what she views as an anthropocentric perspective that assumes that human cognition is the standard against which other uses of psychological ascriptions should be judged. Finally, a fourth view is that appeals to the nature of subjectivity and point of view are key here (Godfrey-Smith 2019; see also Godfrey-Smith 2016c). Godfrey-Smith takes understanding the evolution of subjectivity to be central to advancing responses to “explanatory gap” arguments in the philosophy of mind, implying the graduated nature of cognition itself.

The discussion in section 6 has drawn out more about the conceptual space that physiological individuals occupy and their relationship to evolutionary individuals. This section offers a more complete and integrative overview of that conceptual space. Before populating the running summary diagram with examples of various kinds of biological individuals, we first simply add Darwinian or evolutionary individuals to Figure 3 and label the resulting nine regions in it to arrive at Figure 5 :

Figure 5: Adding Darwinian Individuals. [An extended description of figure 5 is in the supplement.]

As simple as this modification to Figure 3 is, it allows for much more fine-grained answers to the Focal Question, both in terms of the relationship between the subsidiary categories living agents, organisms, and Darwinian individuals, and in terms of where particular individuals are located in the resulting conceptual space. It may turn out that some of these regions are unoccupied by actual biological individuals, or that some of the adjacent regions collapse into one another. But the following proceeds by indicating how the preceding discussion suggests all nine regions are exemplified by distinct kinds of biological individual, moving from less contentious to more contentious examples.

First, consider the lower half of Figure 5 and regions 1, 2 and 3. While organisms are both Darwinian individuals and living agents, there are two different types of Darwinian individuals that are not living agents: some parts of organisms, such as genes (region 2) and, perhaps more controversially, groups such as colonies of eusocial insects (region 3). For example, honey bee colonies appear to be Darwinian individuals even though they are not literally living agents. Each individual bee within a colony is alive, but as suggested by the discussion of living agency in section 6 , it is only by invoking the cognitive metaphor that the whole colony itself can be said to be a living agent.

Second, consider the outermost regions to the left and right of Figure 5 , regions 4 and 5. There are both some parts and some groups of organisms that are neither organisms nor Darwinian individuals nor living agents. Most parts of the cellular machinery possessed by organisms, such as lysosomes (region 4) or ribosomes, are biological individuals that, like genes, are not living agents, but unlike them, are not Darwinian individuals. Groups with this same status include higher taxa, such as species and clades discussed in section 4 . Clades (region 5) are neither organisms nor living agents. And even the most optimistic of clade selectionists will probably agree that a relatively inclusive and diverse taxon such Bryophyta , consisting of about 10,000 moss species, is not itself a Darwinian individual. Yet if the common assumption that monophyletic clades are a type of biological individual is accepted, Bryophyta will nonetheless count as a biological individual (De Luna, Newton, & Mishler 2003 Other Internet Resources ). Bryophyta thus belongs in the far right of Figure 5 .

Third, consider the upper half of Figure 5 and regions 6 and 7. There are correspondingly two different types of living agents that are not Darwinian individuals: some parts of organisms such as hearts (region 6) and (again, perhaps more controversially), groups of organisms such as coral reefs (region 7). As physiological individuals, hearts are alive but they do not reproduce or relate to reproducers in the manner that Darwinian individuals do. As suggested at the end of section 6.1 , a coral reef may also be an example of this kind of biological individual at the group level. Coral reefs don’t feature the type of reproduction-involving life cycles characteristic of organisms, and some of the same facts about reproduction likely disqualify them from being Darwinian individuals. Yet perhaps the reefs (in addition to their constituent individuals) have a better chance than eusocial insect colonies of counting as living agents.

Finally, what of the two remaining regions of Figure 5 , regions 8 and 9? These contain, respectively, biological individuals that are parts of organisms and are both Darwinian individuals and living agents, and organisms that are living agents but not Darwinian individuals. Some viruses are at least plausible candidate examples of the former category (region 8), since they have the internal complexity and unity of function possessed by physiological individuals but employ a scaffolded form of reproduction that relies on the replicative machinery of their host. And perhaps corporate organisms that are typified by tightly integrated multispecies complexes exemplify the latter (region 9). Consider again the Hawaiian bobtail squid plus its colony of Vibrio fischeri bacteria that Godfrey-Smith (2013) discusses as such an example (see Figure 1 above). Those who view this entity as an organism do so because of the intricate integration between squid and bacteria (Nyholm & McFall-Ngai 2004; Bouchard 2010). As such, it seems to be a living agent or physiological individual. But lacking a reproductive life cycle, it is not a Darwinian individual. One might well argue, by contrast, that this feature of the squid- Vibrio complex also disqualifies it as an organism, making it no different in kind from coral reefs. Resolving this issue will turn partly on how exactly different sorts of reproduction are distinguished, and which sorts are required for evolution by natural selection, topics that have recently become more intensely debated (e.g., Godfrey-Smith 2015, 2016b; Griesemer 2014, 2016; O’Malley 2016).

Figure 6 completes this running visual summary of conceptual space that biological individuals occupy, with the addition of a table that associates the regions with the examples discussed above.

Regions with their examples
region	example
1	Fruit fly
2	Gene
3	Eusocial insect colony
4	Lysosome
5	Clades (such as Bryophyta)
6	Heart
7	Coral reef
8	Virus
9	Squid+ bacteria

Figure 6: Biological Individuals in Conceptual Space. [An extended description of figure 6 is in the supplement.]

It was noted at the outset that organism and biological individual have been simply equated by several influential contemporary authors (Queller & Strassmann 2009; Clarke 2012). This section explores their views of the regulation of evolutionary individuals.

David Queller and Joan Strassmann have provided one agenda for the empirical study of what they call “the evolution of organismality” (Queller & Strassmann 2009, 2016; Strassmann & Queller 2010). They begin from the claim that the definitive feature of organisms is the combination of high cooperation and low conflict between their parts (see also Folse & Roughgarden 2010 on organisms). Queller and Strassmann note both that these things are matters of degree and that one can vary independently of the other. They use these parameters to define a two-dimensional space that represents a variety of biological individuals, as Figures 7A and 7B illustrate.

7a: Groups of cells

7b: Groups of multi-cellular individuals

Figure 7: Varying Degrees of Conflict and Cooperation (From Fig. 1 & 2, Queller & Strassmann 2009). [An extended description of figure 7 (A and B) is in the supplement.]

To capture these ideas, it is useful to think of the feature that Queller and Strassmann believe is definitive of biological individuals as the internal ratio : it is the ratio of the level of cooperation between internal parts of individuals to that of the conflict between them. The higher this ratio is, the higher the degree of individuality. Figure 7A indicates that, relative to other groups of cells, a mouse will have a relatively large internal ratio, while a yeast floc will have a relatively small internal ratio.

Since the internal ratio considers only the level of internal control within a biological individual, focusing on it alone neglects the other aspect of autonomous agency that arose in section 6.3 : freedom from external influence. This external dimension to individuality can also be thought of as involving a ratio between cooperation and conflict—not between the parts of the individual but between that individual and other individuals that it interacts with. Just as an individual in Figure 7B with a relatively large internal ratio has a higher level of individuality, according to Queller and Strassmann, so too would an individual with a low external ratio , i.e., one in which external cooperation was low and external conflict was high. To extend Queller and Strassmann’s idea along these lines, the measure of the level of individuality would be a type of meta ratio : the ratio between the internal and external ratios.

This extension of Queller and Strassmann’s view of individuality may prove useful in fleshing out more details of what Godfrey-Smith (borrowing a term of Huxley’s) calls the movement of individuality (2013: 33). This refers to the ways in which new kinds of individual evolve slowly, over geological time scales, from recurring collaborations between different types of Darwinian individuals whose graded nature might be thought puzzling (Molter 2022). Such partnerships sometimes lead to new examples of paradigm individuals, but other times falter or stall at the mere collaboration stage with no new individuals at all. Closure of a pathway to a higher degree of individuality could be brought about by either a drop in the internal ratio (reduced individuality because of internal matters) or a rise in the external ratio (reduced individuality because of external matters). An extension of Queller and Strassman’s idea of organismality being a matter of degree has been deployed recently to tentatively explore the idea of multispecies life cycles in a sketch of some possible pathways from multispecies group configurations to multispecies organisms (Andersson, Isaksson, and Libby 2022).

In effect, Queller and Strassmann have proposed a view of evolutionary individuals that is exclusively focused on the regulation of the parts of an evolutionary individual as a means to avoiding subversion from within. In a series of papers, Ellen Clarke has developed a more integrative view of evolutionary individuals that develops this regulative dimension to biological individuality (Clarke 2010, 2012, 2013, 2016a, 2016b). In work focused on plant individuality, Clarke emphasizes the mechanisms that constrain either sources of heritable variation, such as niche construction, bottlenecks, and polyploidy, or fitness differences, such as investment in root connections and the synchronization of flowering (2012: 351, 356). Clarke then argues that something is an evolutionary individual if and only if it possesses what she calls policing and demarcating mechanisms (2013: 427).

A policing mechanism “is any mechanism that inhibits the capacity of an object to undergo within-object selection” (Clarke 2013: 421), typically by decreasing the genetic variation between parts of an object. This decreases the chance that the object’s parts will undergo selection that disrupts the integration of those parts. There is a sense in which demarcating mechanisms operate in just the opposite way. Rather than working to constrain or limit selective processes amongst an individual’s parts, a demarcating mechanism “increases or maintains the capacity of an object to undergo between-object selection” (2013: 424), doing so by promoting the variation (between objects) that fuels selection.

For Clarke, it is what these two sorts of mechanisms do that is important, not how the mechanisms do this in various ways (Clarke 2013: 429). In other words, it is only the functions of the mechanisms that Clarke thinks are definitive, not the various material ways those functions are realized. As Clarke stresses, this implies the multiple realizability of evolutionary individuals. This “thoroughgoing functionalism about individuality” (Sterner 2015: 610) abstracts away from specific realizations of the functional roles of policing and demarcation. In this respect, Clarke’s view contrasts with many other views of evolutionary individuals that emphasize the importance of particular ways in which these mechanisms are realized. For example, Dawkins, Maynard-Smith, and Bonner imply that certain material bottlenecks—narrowings between generations exemplified by our own single-celled, zygotic bottleneck—are essential ways for policing to be realized in evolutionary individuals (Clarke 2013: 418–419), while Ratcliffe and Kirk instead make material germ-soma separation essential (Clarke 2013: 420).

Clarke’s functionalism thus leads her to reject “the bottleneck condition” as strictly necessary for evolutionary individuality, a condition that Marc Ereshefsky and Makmiller Pedroso also reject as part of their defense of the view that multispecies biofilms are evolutionary individuals (Ereshefsky & Pedroso 2013, 2015). Clarke’s functionalism thus in principle facilitates the search for alternative mechanisms—perhaps such as lateral gene transfer in the case of biofilms—that serve that function in contexts where the usual material bottlenecks are not present.

This makes all the more interesting Clarke’s own disagreement with those who have defended the idea that biofilms are evolutionary individuals (Clarke 2016a), wherein she argues that many of the important claims that underpin ascriptions of multicellularity to biofilms—such as that they are physiologically unified systems or contain cells that interact synergistically—are either not verifiable (e.g., they have higher-level adaptions) or are false (e.g., they display heritable variation in fitness). While Clarke’s functionalism means that she remains open to the suggestion that there may be some non-genetic form of heritability in biofilms (Doolittle 2013), she takes the relevant empirical evidence here to be indecisive (Clarke 2016a: 202).

Finally, the evolution of biological individuality continues to be a lively topic (Okasha 2011; Calcott & Sterelny 2011; Bourrat 2015; Clarke 2016b; O’Malley & Powell 2016; Queller & Strassmann 2016; Herron 2017, 2021; Sterner 2017). The starting point here is the idea that the history of life is the history of the construction of more complicated biological individuals from simpler individuals, with natural selection, operating at one or more levels, facilitating the transitions between these individuals (Buss 1987; Maynard Smith and Szathmáry 1995). Underlying these ideas is the assumption that many or all biological individuals are hierarchically organized: earlier individuals provide the material basis for later individuals. For example, prokaryotes, which are single-celled organisms without a nucleus, form the material basis for single-celled eukaryotes, which do have a nucleus; in turn, single-celled eukaryotes serve as the material basis for multicellular eukaryotes (Herron, Conlin, and Ratcliff 2022).

The evolution of biological individuals from prokaryotes to single-celled eukaryotes around 2 billion years ago, and from those to multicellular eukaryotes in the last 600–800 million years, are established facts. In addition, there appear to be no counter-examples to this evolutionary trend. Yet speculation and controversy surround almost everything else that has been said about these evolutionary transitions. Consider five such issues on which there is a sort of default position in the literature that remains subject to ongoing philosophical and empirical interrogation.

First, it has been common to think, especially in work from and influenced by Richard Michod (e.g., Michod 2005), that at the heart of an evolutionary transition is some kind of fitness transfer or decoupling, with the fitness of new, “collective” evolutionary individuals increasing relative to that of the “particles” from which they evolve until the two are decoupled. Work by Matthew Herron and colleagues on nascent life cycles (Ratcliff et al. 2017) and the evolution of multicellularity (Herron, Conlin, and Ratcliff 2022) that speculates on the intermediate processes driving evolutionary transitions are anchored within this framework. This conception of evolutionary transitions and the modelling frameworks in which it operates has been challenged by Pierre Bourrat and colleagues (Black, Bourrat, and Rainey 2020; Bourrat 2019; Bourrat et al. 2022), who look instead to trait-based tradeoff breaking as an alternative indicator of evolutionary transitions in individuality. Here ecological scaffolding and population structure play critical roles in mediating the extended process of a major evolutionary transition that is “Darwin-like”, becoming moreso with the endogenization of the processes so scaffolded (Bourrat forthcoming, 2023).

Second, it is typically assumed that the evolution of individuality itself is the evolution of complexity. There are, however, questions both about how complexity itself should be measured or conceived and about what empirical evidence there is for viewing the complexity of individuals as increasing over evolutionary time (McShea 1991). Are the number of cell types that an individual has considered (Bonner 1988), the types of hierarchical organization it manifests (Maynard Smith 1988), or some more taxa-specific criterion, such as the information required to specify the diversity of limb-pair types (Cisne 1974)? Fossils constitute a principal source for the criteria that have been proposed here. Yet different kinds of organisms leave fossils with distinct kinds of features, and some kinds of organisms are more likely to leave fossils than are others.

One natural suggestion is that there may well be different kinds of hierarchies for the evolution of individuality, since kinds of individuals can differ from one another in more than one way. Daniel McShea (2001a, 2001b; McShea & Changizi 2003) has proposed a structural hierarchy that is based on two components, the number of levels of nestedness and the degree to which the highest individual in the nesting is individuated or developed. McShea provides an overarching framework in which eukaryotic cells can be viewed as evolving from differentiated aggregations of prokaryotic cells that have intermediate parts; multicellular eukaryotes as evolving from differentiated aggregations of single-celled eukaryotes; and colonial eukaryotes as evolving from differentiated aggregations of multicellular eukaryotes.

By contrast, Maynard Smith and Szathmáry (1995) focus on differences in how genetic information is transmitted across generations, proposing eight major transitions in the history of life. These start with the transition from replicating molecules to compartmentalized populations of such molecules, and end with the transition from primate societies to human societies. While Maynard Smith and Szathmáry are interested in individuality and complexity, their eight transitions do not form a continuous, non-overlapping hierarchy. Their discussion is focused primarily on exploring the processes governing each of the particular transitions they propose in terms of changes in replicative control. O’Malley and Powell (2016) have recently argued that not only does this perspective omit critical events—such as the acquisition of mitochondria and plastids, in what those authors prefer to think of as turns rather than transitions in the evolution of living things—but also that what is needed is a

supplementary perspective that is less hierarchical, less focused on multicellular events, less replication oriented, and in particular, more metabolic. (O’Malley and Powell 2016: 175)

Third, there is the question of just what processes and events should be included as evolutionary transitions, major or otherwise. Some have argued, for example, that the origin of oxygen-generating photosynthesis should be added to the major transitions (e.g., O’Malley and Powell 2016; see Szathmáry and Fernando 2011 for a longer list of additions). Pushing back against the trend to propose a more expansive list of major evolutionary transitions, whether mediated by the loosening of existing criteria or by general pluralistic tendencies that we’ve seen emerge in the literature on biological individuals in various ways, Herron (2021) has recently argued for a narrowing of the definition of a major transition by requiring that it lead to the creation of a new population of evolutionary individuals, drawing on an analogy with what happened in 2006 with the exclusion of Pluto from the category “planet” as a motivating intuition pump. On this view, neither the origins of the genetic code nor the origin of language, both major transitions according to Maynard Smith and Szathmáry (1995), belong on the list of major evolutionary transitions, independent of their overall evolutionary significance.

Fourth, it is common to view the trend from prokaryotes to multicellular eukaryotes as resulting from some type of directional bias, one that makes the trend a tendency supported by underlying mechanisms and constraints. Perhaps the tendency is underwritten by thermodynamic, energetic considerations, by facts about the generative entrenchment of developmental systems (Griffiths & Gray 2001), or by evolutionary advantages of increases in size (McShea 1998). But in supposing that there is some type of directional bias, each of these hypotheses might be thought committed to the sort of Panglossianism about adaptation that Gould and Lewontin (1979) are famous for critiquing, or (more subtly) to a view of evolutionary change as progressive or inevitable in some way. Gould has used his discussion of the Burgess Shale (Gould 1989) to challenge such views of evolution, arguing that the disparity of the fossils in that shale indicates that living things are significantly less different from one another than they once were. Gould argues that the range of biological individuals now on the planet is largely the result of highly contingent extinction events, and there should be wariness of immediately assuming that observed trends or patterns are adaptive (or other) tendencies.

Fifth, many authors have recognized that whatever trends or tendencies there are in the evolution of individuals, there have also been changes over evolutionary time in the social relations between individuals (e.g., Frank 1998), and in the sorts of shared resources that are available to the biological individuals that Douglas Erwin has discussed drawing on the economic concepts of public goods and club goods (Erwin 2015, McInerney & Erwin 2017). Yet how sociality should be integrated into a view of the evolution of biological individuals remains under-theorized (for recent exceptions, see Birch 2017, Okasha 2018, and Lloyd and Wade 2019). And however limited fossil evidence for individual structures and ecological niches may be, such evidence for the kinds and extent of sociality is significantly more sparse. Much of the work to be done here seems distinctly philosophical in that it concerns how sociality is conceptualized. Should one accept the simple aggregation of individuals as a basic form of sociality? Does sociality essentially involve some form of cooperation, and if not, what is the relationship between “prosocial” sociality and antagonistic forms of sociality (e.g., competition or predation)? Although the “evolution of sociality” has been taken up by animal biologists (especially by primatologists) and evolutionary anthropologists (where it is often viewed game-theoretically), this has served to reinforce a view of sociality that seems somewhat narrow, e.g., the view is not clearly applicable to structurally simpler individuals. Perhaps the idea that sociality is not a relatively recent addition to multicellular life needs to be taken seriously. Instead, sociality may be a more sweeping feature of many if not all biological individuals, with the evolution of individuality understood in tandem with the idea of changing, shared, public and club goods. This would make for a more dynamic and cyclical view of the history of life than has been assumed in past thinking about biological individuals.

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Towards a comprehensive definition of pandemics and strategies for prevention: a historical review and future perspectives.

1. Introduction

2. smallpox, 2.1. antonine plague (165–180 ad), 2.2. smallpox taking over the world, 2.3. smallpox in the americas (1520–1880 ad), 2.4. steps to the smallpox eradication, 3.1. justinian plague (541–750 ad), 3.2. black death (1338–1353 ad), 3.3. third plague (1855–1960 ad), 4.1. first cholera pandemic (1817–1824 ad), 4.2. second cholera pandemic (1826–1835 ad), 4.3. third cholera pandemic (1839–1860 ad), 4.4. forth cholera pandemic (1863–1875 ad), 4.5. fifth cholera pandemic (1881–1896 ad), 4.6. sixth cholera pandemic (1899–1923 ad), 4.7. seventh cholera pandemic (1961 ad–today), 5. influenza, 5.1. russian flu (1889–1890 ad), 5.2. spanish flu (1918–1920 ad), 5.3. asian flu (1957–1958 ad), 5.4. hong kong flu (1968–1969 ad), 5.5. russian flu (1977–1979 ad), 5.6. swine flu (2009–2010 ad), 6. aids (1981–today), 7. coronaviruses, 7.1. severe acute respiratory syndrome (sars) (2002–2004 ad), 7.2. middle east respiratory syndrome (mers) (2012 ad–today), 7.3. covid-19 (2019–2023 ad), 8. discussion, 9. conclusions, supplementary materials, data availability statement, acknowledgments, conflicts of interest.

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Dias, R.A. Towards a Comprehensive Definition of Pandemics and Strategies for Prevention: A Historical Review and Future Perspectives. Microorganisms 2024 , 12 , 1802. https://doi.org/10.3390/microorganisms12091802

Dias RA. Towards a Comprehensive Definition of Pandemics and Strategies for Prevention: A Historical Review and Future Perspectives. Microorganisms . 2024; 12(9):1802. https://doi.org/10.3390/microorganisms12091802

Dias, Ricardo Augusto. 2024. "Towards a Comprehensive Definition of Pandemics and Strategies for Prevention: A Historical Review and Future Perspectives" Microorganisms 12, no. 9: 1802. https://doi.org/10.3390/microorganisms12091802

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the functional role and position of a species (population) within a community or ecosystem, including what resources it uses, how and when it uses the resources, and how it interacts with other populations. Study with Quizlet and memorize flashcards containing terms like species richness, relative abundance, individualistic hypothesis and more.
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