Group selection
In evolutionary biology, group selection refers to the idea that allele
An allele is one of two or more forms of a gene or a genetic locus . "Allel" is an abbreviation of allelomorph. Sometimes, different alleles can result in different observable phenotypic traits, such as different pigmentation...

s can become fixed or spread in a population because of the benefits they bestow on groups, regardless of the alleles' effect on the fitness
Fitness (biology)
Fitness is a central idea in evolutionary theory. It can be defined either with respect to a genotype or to a phenotype in a given environment...

 of individuals within that group.

Group selection was used as a popular explanation for adaptations, especially by V. C. Wynne-Edwards. For several decades, however, critiques, particularly by George C. Williams
George C. Williams
Professor George Christopher Williams was an American evolutionary biologist.Williams was a professor emeritus of biology at the State University of New York at Stony Brook. He was best known for his vigorous critique of group selection. The work of Williams in this area, along with W. D...

, John Maynard Smith
John Maynard Smith
John Maynard Smith,His surname was Maynard Smith, not Smith, nor was it hyphenated. F.R.S. was a British theoretical evolutionary biologist and geneticist. Originally an aeronautical engineer during the Second World War, he took a second degree in genetics under the well-known biologist J.B.S....

 and C.M. Perrins (1964), cast serious doubt on group selection as a major mechanism of evolution
Evolution is any change across successive generations in the heritable characteristics of biological populations. Evolutionary processes give rise to diversity at every level of biological organisation, including species, individual organisms and molecules such as DNA and proteins.Life on Earth...

, and though some scientists have pursued the idea over the last few decades, only recently have group selection models seen a resurgence.


Specific syndromes of selective factors can create situations where groups are selected because they display group properties that are selected-for. Some mosquito-transmitted rabbit viruses, for instance, are only transmitted to uninfected rabbits from infected rabbits that are still alive. This creates a selective pressure on every group of viruses already infecting a rabbit not to become too virulent and kill their host rabbit before enough mosquitoes have bitten it. In natural systems such viruses display much lower virulence levels than do mutants of the same viruses that in laboratory culture readily out-compete non-virulent variants (or than do tick-transmitted viruses—ticks, unlike mosquitoes, bite dead rabbits).

However, theoretical models of the 1960s seemed to imply that the effect of group selection was negligible. Allele
An allele is one of two or more forms of a gene or a genetic locus . "Allel" is an abbreviation of allelomorph. Sometimes, different alleles can result in different observable phenotypic traits, such as different pigmentation...

s are likely to be held on a population-wide level, leaving nothing for group selection to select for. Additionally, generation time is much longer for groups than it is for individuals. Assuming conflicting selection pressures, individual selection will occur much faster, swamping any changes potentially favored by group selection. The Price equation
Price equation
The Price equation is a covariance equation which is a mathematical description of evolution and natural selection. The Price equation was derived by George R. Price, working in London to re-derive W.D. Hamilton's work on kin selection...

 can partition variance caused by natural selection at the individual level and the group level, and individual level selection generally causes greater effects.

Experimental results starting in the late 1970s demonstrated that group selection was far more effective than the then-current theoretical models had predicted. A review of this experimental work has shown that the early group selection models were flawed because they assumed that genes acted independently, whereas in the experimental work it was apparent that gene interaction, and more importantly, genetically based interactions among individuals, were an important source of the response to group selection (e.g.). As a result many are beginning to recognize that group selection, or more appropriately multilevel selection, is potentially an important force in evolution.

More recently, Yaneer Bar-Yam
Yaneer Bar-Yam
Yaneer Bar-Yam is an American physicist, systems scientist, and founding president of the New England Complex Systems Institute.-Biography:...

 has claimed that the gene-centered view (and thus Ronald Fisher
Ronald Fisher
Sir Ronald Aylmer Fisher FRS was an English statistician, evolutionary biologist, eugenicist and geneticist. Among other things, Fisher is well known for his contributions to statistics by creating Fisher's exact test and Fisher's equation...

's treatment of evolution) relies upon a mathematical approximation that is not generally valid. Bar-Yam argues that the approximation is a dynamic form of the Mean Field approximation
Mean field theory
Mean field theory is a method to analyse physical systems with multiple bodies. A many-body system with interactions is generally very difficult to solve exactly, except for extremely simple cases . The n-body system is replaced by a 1-body problem with a chosen good external field...

 frequently used in physics and whose limitations are recognized there. In biology, the approximation breaks down when there are spatial populations resulting in inhomogeneous genetic types (called symmetry breaking
Symmetry breaking
Symmetry breaking in physics describes a phenomenon where small fluctuations acting on a system which is crossing a critical point decide the system's fate, by determining which branch of a bifurcation is taken. To an outside observer unaware of the fluctuations , the choice will appear arbitrary...

 in physics). Such symmetry breaking may also correspond to speciation
Speciation is the evolutionary process by which new biological species arise. The biologist Orator F. Cook seems to have been the first to coin the term 'speciation' for the splitting of lineages or 'cladogenesis,' as opposed to 'anagenesis' or 'phyletic evolution' occurring within lineages...


Spatial populations of predators and prey have also been shown to show restraint of reproduction at equilibrium, both individually and through social communication, as originally proposed by Wynne-Edwards. While these spatial populations do not have well-defined groups for group selection, the local spatial interactions of organisms in transient groups are sufficient to lead to a kind of multi-level selection. There is however as yet no evidence that these processes operate in the situations where Wynne-Edwards posited them; Rauch et al.'s analysis, for example, is of a host-parasite situation, which was recognised as one where group selection was possible even by E. O. Wilson
E. O. Wilson
Edward Osborne Wilson is an American biologist, researcher , theorist , naturalist and author. His biological specialty is myrmecology, the study of ants....

 (1975), in a treatise broadly hostile to the whole idea of group selection. Specifically, the parasites do not individually moderate their transmission; rather, more transmissible variants "continually arise and grow rapidly for many generations but eventually go extinct before dominating the system."

The haystack model and trait groups

Maynard Smith can be credited with what has become known as the "haystack model" of group selection. As a non-mathematical introduction to the idea, imagine a group of animals that spend most of their time living and breeding in haystacks but that occasionally all come out of their haystacks simultaneously, mix together and then separate into equal groups, which once again go off to inhabit separate haystacks. We can then imagine a trait that benefits each haystack group, perhaps leading to behaviorally altruistic acts that cost an individual some fitness but enhance the fitness of its group even more, and a selfish trait that, for the purposes of this discussion, we can call the absence of the altruistic trait.

Each of these two traits works on a different level of selection. Within the individual haystacks the selfish organisms benefit in terms of evolutionary fitness. This is because the selfish organisms benefit from the actions of the altruistic organisms but do not pay any of the evolutionary costs for being altruistic (sacrificing some good for that of others). Thus, in each generation the number of altruists in the group would shrink compared to the number of selfish organisms. As a result one might first think that a group beneficial trait, especially an altruistic one, would be doomed to eventually die out. But we must remember the strange nature of these hypothetical organisms. Every so often, at the same time, all the members of all the haystacks form one large group, randomly assort into equal groups, and then move back into the haystacks. Because of this an altruistic behavior can take hold by the following reasoning. While the number of selfish organisms in each haystack increases in percentage every generation, the total population of haystacks that contain altruists produce more offspring over all than those that do not. This means that populations with altruists are going to be over-represented when all the haystacks are abandoned to form a larger group. So long as the number of generations spent in each haystack is not so long as to dramatically reduce the number of altruists, and so long as the group benefit of the altruistic trait is significant enough, the number of altruists in all the haystack populations can rise.

However, though Maynard Smith gave a mathematical model by which group selection might work, he was skeptical that it would happen in nature often enough to be worth considering. His reasoning was that the specific conditions for group selection to take hold, namely the repeated isolation, mixture, and reisolation of organisms would be so rare and unlikely to occur in nature that it was almost certainly not a significant evolutionary force.

In their 1998 book Unto Others, and in various articles before this, Sober and David Sloan Wilson
David Sloan Wilson
David Sloan Wilson is an American evolutionary biologist and a Distinguished Professor of Biological Sciences and Anthropology at Binghamton University. He is a son of the author Sloan Wilson.-Academic career:...

 challenge this view. While one of their challenges takes the form of naming organisms, such as the so called "brain worm" (Dicrocoelium dendriticum
Dicrocoelium dendriticum
The Lancet liver fluke is a parasite fluke that tends to live in cattle or other grazing mammals.- History of discovery :...

), which has a life cycle much like that of the haystack organisms above, they present a more significant argument, based on the notion of trait groups.

Trait groups can occur within larger groups through the interaction of particular genetic traits, and need not interact for a generation to promote survival value. Sober and Wilson see kin selection
Kin selection
Kin selection refers to apparent strategies in evolution that favor the reproductive success of an organism's relatives, even at a cost to the organism's own survival and reproduction. Charles Darwin was the first to discuss the concept of group/kin selection...

, which is often considered an alternative to group selection, as a special case of a trait groups. To see how a trait group could be beneficial, let's imagine an altruist trait, such as cooperation with another organism even in such cases where it only benefits 40% as much as the organism it helps, and a selfish trait such as cooperating with another organism only when it will benefit more than the organism it helps. The first trait is considered altruistic in Sober and Wilson’s sense because the within-group fitness of the altruistic organism drops every time it cooperates compared with the other member of the group. Now imagine five organisms, one of which is altruistic in regards to this trait, and the rest of which are selfish. Assume that each case of cooperation increases the chance of survival and reproduction by 10 units, which is divided among the interacting pair (group of two). Now assume that member of the population groups/interacts with each other member of the population one time. After all the interactions have taken place, the selfish organisms have each acquired 6 units. This is because they all refuse to cooperation with other selfish members (since it is impossible for both members to benefit more than the other), but each takes advantage of the altruist benefits over that individual in a ratio of 60% to 40%. The altruist on the other hand has interacted with 4 selfish organisms and thus has earned 16 units (four for each encounter) and thus has a greater survival advantage than the selfish members of the population. The altruist ends up winning the survival "war" even though it came out behind in every survival "battle".

Because individuals can form hundreds or even thousands of trait groups within its life span, the trait group selection model does not have to rely on the unlikely situation of an entire population isolating into groups, merging, and then isolating into groups again. Likewise the rate at which trait groups can form and dissolve can be many times faster than the rate at which individuals reproduce, providing cumulative as opposed to all-or-nothing benefits.
It is important to note that this argument has not settled the issue of group selection however. There is still heavy debate as to whether or not such formations count as “real” groups in the traditional biological sense of groups affected by group selection.

Multilevel selection theory

In recent years, the limitations of earlier models have been addressed, and newer models suggest that selection may sometimes act above the gene level. Recently David Sloan Wilson
David Sloan Wilson
David Sloan Wilson is an American evolutionary biologist and a Distinguished Professor of Biological Sciences and Anthropology at Binghamton University. He is a son of the author Sloan Wilson.-Academic career:...

 and Elliot Sober have argued that the case against group selection has been overstated. They focus their argument on whether groups can have functional organization in the same way individuals do and, consequently, whether groups can also be "vehicles" for selection
In the context of evolution, certain traits or alleles of genes segregating within a population may be subject to selection. Under selection, individuals with advantageous or "adaptive" traits tend to be more successful than their peers reproductively—meaning they contribute more offspring to the...

. For example, groups that cooperate better may have out-reproduced those that did not. Resurrected in this way, Wilson & Sober's new group selection is usually called multilevel selection theory.

David Sloan Wilson, the developer of Multilevel Selection Theory (MLS) compares the many layers of competition and evolution to the “Russian Matryoska Dolls” within one another. The lowest level is the genes, next come the cells, and then the organism level and finally the groups. The different levels function cohesively to maximize fitness, or reproductive success. After establishing these levels, MLS goes further by saying that selection for the group level, which is competition between groups, must outweigh the individual level, which is individuals competing within a group, for a group-beneficiating trait to spread. MLS theory focuses on the phenotype this way because it looks at the levels that selection directly acts upon.

MLS theory does not lean towards individual or group selection but can be used to evaluate the balance between group selection and individual selection on a case-by-case scenario. Some experiments done imply that group selection can prevail, such as the experiment conducted by William Muir of Purdue University comparing egg productivity in hens. In the experiment, he demonstrates the existence of group selection by showing that in individual selection, a hyper-aggressive strain had been produced that led to many fatal attacks only after six generations. Group selection has been most often postulated in humans and, notably, social insects that make cooperation a driving force of their adaptations over time.

For humans, a highly pro-social, cognitive thinking species, social norms can be seen as a means of reducing the individual level variation and competition and shift selection in humans to the group level. Wilson ties the MLS theory regarding humans to another upcoming theory known as gene-culture evolution by acknowledging that culture seems to characterize a group-level mechanism for human groups to adapt to environmental changes. Methods of testing MLS include social psychological experimentation and multilevel modeling equations.

Wilson & Sober's work has been part of a revival of interest in multilevel selection as an explanation for evolutionary phenomena. Indeed, in a 2005 article, E. O. Wilson argued that kin selection could no longer be thought of as underlying the evolution of extreme sociality, for two reasons. First, some authors have shown that the argument that haplodiploid inheritance, characteristic of the Hymenoptera
Hymenoptera is one of the largest orders of insects, comprising the sawflies, wasps, bees and ants. There are over 130,000 recognized species, with many more remaining to be described. The name refers to the heavy wings of the insects, and is derived from the Ancient Greek ὑμήν : membrane and...

, creates a strong selection pressure towards nonreproductive castes is mathematically flawed. Second, eusociality no longer seems to be confined to the hymenopterans; increasing numbers of highly social taxa have been found in the years since Wilson's foundational text on sociobiology was published in 1975, including a variety of insect species, as well as a rodent species (the naked mole rat
Naked Mole Rat
The naked mole rat , also known as the sand puppy or desert mole rat, is a burrowing rodent native to parts of East Africa and the only species currently classified in the genus Heterocephalus...

). Wilson suggests the equation for Hamilton's rule:
rb > c

(where b represents the benefit to the recipient of altruism, c the cost to the altruist, and r their degree of relatedness) should be replaced by the more general equation
(rbk + be) > c

in which bk is the benefit to kin (b in the original equation) and be is the benefit accruing to the group as a whole. He then argues that, in the present state of the evidence in relation to social insects, it appears that be>rbk, so that altruism needs to be explained in terms of selection at the colony level rather than at the kin level. However, it is well understood in social evolution theory that kin selection and group selection are not distinct processes, and that the effects of multi-level selection are already fully accounted for in Hamilton's original rule, rb>c.

Group selection indicated by gene-culture coevolution

Gene-culture coevolution is a modern hypothesis (applicable mostly to humans) that combines evolutionary biology and modern sociobiology to indicate group selection. It treats culture as a separate evolutionary system that acts in parallel to the usual genetic evolution to transform human traits. It is believed that this approach of combining genetic influence with cultural influence over several generations is not present in the other hypotheses such as reciprocal altruism and kin selection, making gene-culture evolution one of the strongest realistic hypotheses for group selection. Fehr provides evidence of group selection taking place in humans presently with experimentation through logic games such as prisoner’s dilemma, the type of thinking that humans have developed many generations ago.

Gene-culture coevolution, or cumulative cultural evolution, allows humans to culturally evolve highly distinct adaptations to the local pressures and environments much quicker than with genetic evolution alone. Robert Boyd
Robert Boyd
-Noblemen:* Robert Boyd, 1st Lord Boyd , Scottish statesman* Robert Boyd, 4th Lord Boyd , Scottish nobleman, grandson of the 1st Lord Boyd* Robert Boyd, 5th Lord Boyd , Scottish nobleman* Robert Boyd, 7th Lord Boyd...

 and Peter J. Richerson, two strong proponents of cultural evolution, postulate that the act of social learning, or learning in a group as done in group selection, allows human populations to accrue information over many generations. This leads to the cultural evolution of highly adaptive behaviors and technology alongside genetic evolution. Specifically, they believe that the ability to collaborate with each other evolved during the Middle Pleistocene, a million years ago, in response to a rapidly-changing climate.

Herbert Gintis
Herbert Gintis
Herbert Gintis is an American behavioral scientist, educator, and author. He is notable for his foundational views on Altruism, Cooperation, Epistemic Game Theory, Gene-culture coevolution, Efficiency wages, Strong reciprocity, and Human capital theory. Gintis has also written extensively on...

 approaches cultural evolution of group selection in a much more statistical approach to prove that societies that promote pro-social norms, as in group selection, have higher survival rates than societies that do not. He does so by developing a multilevel gene-culture coevolutionary model that explains the process whereby altruistic social norms will hinder socially harmful and fitness reducing norms and consequently will be internalized. In his equations, he differentiates between a genetic group selection model that is sensitive to group size and migration rates versus his own model that is much less affected by these constraints and therefore more accurate.

Group selection due to differing ESSs

The problem with group selection is that for a whole group to get a single trait, it must spread through the whole group first by regular evolution
Evolution is any change across successive generations in the heritable characteristics of biological populations. Evolutionary processes give rise to diversity at every level of biological organisation, including species, individual organisms and molecules such as DNA and proteins.Life on Earth...

. But, as J. L. Mackie
J. L. Mackie
John Leslie Mackie was an Australian philosopher, originally from Sydney. He made significant contributions to the philosophy of religion, metaphysics, and the philosophy of language, and is perhaps best known for his views on meta-ethics, especially his defence of moral skepticism.He authored six...

 suggested, when there are many different groups, each with a different Evolutionarily Stable Strategy
Evolutionarily stable strategy
In game theory and behavioural ecology, an evolutionarily stable strategy , which is sometimes also called an evolutionary stable strategy, is a strategy which, if adopted by a population of players, cannot be invaded by any alternative strategy that is initially rare. An ESS is an equilibrium...

 (ESS), there is selection between the different ESSs, since some are worse than others. For example, a group where altruism arose would outcompete a group where every creature acted in its own interest.


The evolutionary biologist Jerry Coyne noted:

Group selection isn’t widely accepted by evolutionists for several reasons. First, it’s not an efficient way to select for traits, like altruistic behavior, that are supposed to be detrimental to the individual but good for the group. Groups divide to form other groups much less often than organisms reproduce to form other organisms, so group selection for altruism would be unlikely to override the tendency of each group to quickly lose its altruists through natural selection favoring cheaters. Further, we simply have little evidence that selection on groups has promoted the evolution of any trait. Finally, other, more plausible evolutionary forces, like direct selection on individuals for reciprocal support, could have made us prosocial. These reasons explain why only a few biologists, like Wilson and E. O. Wilson (no relation), advocate group selection as the evolutionary source of cooperation.

Richard Dawkins
Richard Dawkins
Clinton Richard Dawkins, FRS, FRSL , known as Richard Dawkins, is a British ethologist, evolutionary biologist and author...

 and fellow advocates of the gene-centered view of evolution remain unconvinced about group selection. In particular, Dawkins suggests that group selection fails to make an appropriate distinction between replicators and vehicles.

See also

  • Eva Jablonka
    Eva Jablonka
    Eva Jablonka is a theorist and geneticist, known especially for her interest in epigenetic inheritance. Born in 1952 in Poland, she emigrated to Israel in 1957. She is a professor at the Cohn Institute for the History of Philosophy of Science and Ideas at Tel Aviv University...

  • Group Selection
    Group Selection (book)
    Group Selection is a 1971 book edited by George C. Williams, containing papers written by biologists arguing against the view of group selection as a major force in evolution...

    , a 1971 book, by G. C. Williams, arguing against group selection
  • Collective identity
    Collective identity
    The term collective identity may refer to a variety of concepts. In general however, these concepts generally pertain to phenomena where an individuals' perceived membership in a social group impacts upon their own identity in some way. The idea of a collective identity has received attention in a...

  • Battle trance
    Battle trance
    Battle trance is a term denoting a specific altered state of consciousness that characterizes the psychological state of combatants during a combat situation. In this state, combatants do not feel fear or pain , and all the individual members of group are acting as one collective organism...

Further reading

  • Wilson, D.S. (2006). Human groups as adaptive units: toward a permanent consensus. In P. Carruthers, S. Laurence & S. Stich (Eds.), The Innate Mind: Culture and Cognition. Oxford: Oxford University Press. Full text

External links

  • The Controversy of the Group Selection Theory - a review from the "Science Creative Quarterly" (a blog
    A blog is a type of website or part of a website supposed to be updated with new content from time to time. Blogs are usually maintained by an individual with regular entries of commentary, descriptions of events, or other material such as graphics or video. Entries are commonly displayed in...

  • Link to publications by D.S. Wilson
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