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Group selection

From Wikipedia, the free encyclopedia

https://en.wikipedia.org/wiki/Group_selection#Multilevel_selection_theory

Group selection is a proposed mechanism of evolution in which natural selection acts at the level of the group, instead of at the level of the individual or gene.

Early authors such as V. C. Wynne-Edwards and Konrad Lorenz argued that the behavior of animals could affect their survival and reproduction as groups, speaking for instance of actions for the good of the species. In the 1930s, R.A. Fisher and J.B.S. Haldane proposed the concept of kin selection, a form of altruism from the gene-centered view of evolution, arguing that animals should sacrifice for their relatives, and thereby implying that they should not sacrifice for non-relatives. From the mid-1960s, evolutionary biologists such as John Maynard Smith, W. D. Hamilton, George C. Williams, and Richard Dawkins argued that natural selection acted primarily at the level of the gene. They argued on the basis of mathematical models that individuals would not altruistically sacrifice fitness for the sake of a group unless it would ultimately increase the likelihood of an individual passing on their genes. A consensus emerged that group selection did not occur, including in special situations such as the haplodiploid social insects like honeybees (in the Hymenoptera), where kin selection explains the behaviour of non-reproductives equally well, since the only way for them to reproduce their genes is via kin.

In 1994 David Sloan Wilson and Elliott Sober argued for multi-level selection, including group selection, on the grounds that groups, like individuals, could compete. In 2010 three authors including E. O. Wilson, known for his work on social insects especially ants, again revisited the arguments for group selection. They argued that group selection can occur when competition between two or more groups, some containing altruistic individuals who act cooperatively together, is more important for survival than competition between individuals within each group, provoking a strong rebuttal from a large group of ethologists.

Early developments

Charles Darwin developed the theory of evolution in his book, Origin of Species. Darwin also made the first suggestion of group selection in The Descent of Man that the evolution of groups could affect the survival of individuals. He wrote, "If one man in a tribe... invented a new snare or weapon, the tribe would increase in number, spread, and supplant other tribes. In a tribe thus rendered more numerous there would always be a rather better chance of the birth of other superior and inventive members."

Once Darwinism had been accepted in the modern synthesis of the mid-twentieth century, animal behavior was glibly explained with unsubstantiated hypotheses about survival value, which was largely taken for granted. The naturalist Konrad Lorenz had argued loosely in books like On Aggression (1966) that animal behavior patterns were "for the good of the species", without actually studying survival value in the field. Richard Dawkins noted that Lorenz was a "'good of the species' man" so accustomed to group selection thinking that he did not realize his views "contravened orthodox Darwinian theory". The ethologist Niko Tinbergen praised Lorenz for his interest in the survival value of behavior, and naturalists enjoyed Lorenz's writings for the same reason. In 1962, group selection was used as a popular explanation for adaptation by the zoologist V. C. Wynne-Edwards. In 1976, Richard Dawkins wrote a well-known book on the importance of evolution at the level of the gene or the individual, The Selfish Gene.

From the mid-1960s, evolutionary biologists argued that natural selection acted primarily at the level of the individual. In 1964, John Maynard Smith,^[11] C. M. Perrins (1964), and George C. Williams in his 1966 book Adaptation and Natural Selection cast serious doubt on group selection as a major mechanism of evolution; Williams's 1971 book Group Selection assembled writings from many authors on the same theme.

It was at that time generally agreed that this was the case even for eusocial insects such as honeybees, which encourages kin selection, since workers are closely related.

Kin selection and inclusive fitness theory

Experiments from the late 1970s suggested that selection involving groups was possible. Early group selection models assumed that genes acted independently, for example a gene that coded for cooperation or altruism. Genetically based reproduction of individuals implies that, in group formation, the altruistic genes would need a way to act for the benefit of members in the group to enhance the fitness of many individuals with the same gene. But it is expected from this model that individuals of the same species would compete against each other for the same resources. This would put cooperating individuals at a disadvantage, making genes for cooperation likely to be eliminated. Group selection on the level of the species is flawed because it is difficult to see how selective pressures would be applied to competing/non-cooperating individuals.

Kin selection between related individuals is accepted as an explanation of altruistic behavior. R.A. Fisher in 1930 and J.B.S. Haldane in 1932 set out the mathematics of kin selection, with Haldane famously joking that he would willingly die for two brothers or eight cousins. In this model, genetically related individuals cooperate because survival advantages to one individual also benefit kin who share some fraction of the same genes, giving a mechanism for favoring genetic selection.

Inclusive fitness theory, first proposed by W. D. Hamilton in the early 1960s, gives a selection criterion for evolution of social traits when social behavior is costly to an individual organism's survival and reproduction. The criterion is that the reproductive benefit to relatives who carry the social trait, multiplied by their relatedness (the probability that they share the altruistic trait) exceeds the cost to the individual. Inclusive fitness theory is a general treatment of the statistical probabilities of social traits accruing to any other organisms likely to propagate a copy of the same social trait. Kin selection theory treats the narrower but simpler case of the benefits to close genetic relatives (or what biologists call 'kin') who may also carry and propagate the trait. A significant group of biologists support inclusive fitness as the explanation for social behavior in a wide range of species, as supported by experimental data. An article was published in Nature with over a hundred coauthors.

One of the questions about kin selection is the requirement that individuals must know if other individuals are related to them, or kin recognition. Any altruistic act has to preserve similar genes. One argument given by Hamilton is that many individuals operate in "viscous" conditions, so that they live in physical proximity to relatives. Under these conditions, they can act altruistically to any other individual, and it is likely that the other individual will be related. This population structure builds a continuum between individual selection, kin selection, kin group selection and group selection without a clear boundary for each level. However, early theoretical models by D.S. Wilson et al. and Taylor showed that pure population viscosity cannot lead to cooperation and altruism. This is because any benefit generated by kin cooperation is exactly cancelled out by kin competition; additional offspring from cooperation are eliminated by local competition. Mitteldorf and D. S. Wilson later showed that if the population is allowed to fluctuate, then local populations can temporarily store the benefit of local cooperation and promote the evolution of cooperation and altruism. By assuming individual differences in adaptations, Yang further showed that the benefit of local altruism can be stored in the form of offspring quality and thus promote the evolution of altruism even if the population does not fluctuate. This is because local competition among more individuals resulting from local altruism increases the average local fitness of the individuals that survive.

Another explanation for the recognition of genes for altruism is that a single trait, group reciprocal kindness, is capable of explaining the vast majority of altruism that is generally accepted as "good" by modern societies. The phenotype of altruism relies on recognition of the altruistic behavior by itself. The trait of kindness will be recognized by sufficiently intelligent and undeceived organisms in other individuals with the same trait. Moreover, the existence of such a trait predicts a tendency for kindness to unrelated organisms that are apparently kind, even if the organisms are of another species. The gene need not be exactly the same, so long as the effect or phenotype is similar. Multiple versions of the gene—or even meme—would have virtually the same effect. This explanation was given by Richard Dawkins as an analogy of a man with a green beard. Green-bearded men are imagined as tending to cooperate with each other simply by seeing a green beard, where the green beard trait is incidentally linked to the reciprocal kindness trait.

Multilevel selection theory

Kin selection or inclusive fitness is accepted as an explanation for cooperative behavior in many species, but the scientist David Sloan Wilson argues that human behavior is difficult to explain with only this approach. In particular, he claims it does not seem to explain the rapid rise of human civilization. Wilson has argued that other factors must also be considered in evolution. Wilson and others have continued to develop group selection models.

Early group selection models were flawed because they assumed that genes acted independently; but genetically based interactions among individuals are ubiquitous in group formation because genes must cooperate for the benefit of association in groups to enhance the fitness of group members. Additionally, group selection on the level of the species is flawed because it is difficult to see how selective pressures would be applied; selection in social species of groups against other groups, rather than the species entire, seems to be the level at which selective pressures are plausible. On the other hand, kin selection is accepted as an explanation of altruistic behavior. Some biologists argue that kin selection and multilevel selection are both needed to "obtain a complete understanding of the evolution of a social behavior system".

In 1994 David Sloan Wilson and Elliott Sober argued that the case against group selection had been overstated. They considered whether groups can have functional organization in the same way as individuals, and consequently whether groups can be "vehicles" for selection. They do not posit evolution on the level of the species, but selective pressures that winnow out small groups within a species, e.g. groups of social insects or primates. Groups that cooperate better might survive and reproduce more than those that did not. Resurrected in this way, Wilson & Sober's new group selection is called multilevel selection theory.

In 2010, Martin Nowak, C. E. Tarnita and E. O. Wilson argued for multi-level selection, including group selection, to correct what they saw as deficits in the explanatory power of inclusive fitness. A response from 137 other evolutionary biologists argued "that their arguments are based upon a misunderstanding of evolutionary theory and a misrepresentation of the empirical literature".

Wilson compared the layers of competition and evolution to nested sets of Russian matryoshka dolls. The lowest level is the genes, next come the cells, then the organism level and finally the groups. The different levels function cohesively to maximize fitness, or reproductive success. The theory asserts that selection for the group level, involving competition between groups, must outweigh the individual level, involving individuals competing within a group, for a group-benefiting trait to spread.

Multilevel selection theory focuses on the phenotype because it looks at the levels that selection directly acts upon. For humans, social norms can be argued to reduce individual level variation and competition, thus shifting selection to the group level. The assumption is that variation between different groups is larger than variation within groups. Competition and selection can operate at all levels regardless of scale. Wilson wrote, "At all scales, there must be mechanisms that coordinate the right kinds of action and prevent disruptive forms of self-serving behavior at lower levels of social organization."^[25] E. O. Wilson summarized, "In a group, selfish individuals beat altruistic individuals. But, groups of altruistic individuals beat groups of selfish individuals."

Wilson ties the multilevel selection theory regarding humans to another theory, gene–culture coevolution, by acknowledging that culture seems to characterize a group-level mechanism for human groups to adapt to environmental changes.

MLS theory can be used to evaluate the balance between group selection and individual selection in specific cases. An experiment by William Muir compared egg productivity in hens, showing that a hyper-aggressive strain had been produced through individual selection, leading to many fatal attacks after only six generations; by implication, it could be argued that group selection must have been acting to prevent this in real life. Group selection has most often been postulated in humans and, notably, eusocial Hymenoptera that make cooperation a driving force of their adaptations over time and have a unique system of inheritance involving haplodiploidy that allows the colony to function as an individual while only the queen reproduces.

Wilson and Sober's work revived interest in multilevel selection. 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, he suggested, the argument that haplodiploid inheritance (as in the Hymenoptera) 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 Sociobiology: A New Synthesis was published in 1975. These including a variety of insect species, as well as two rodent species (the naked mole-rat and the Damaraland mole rat). 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

rb_k + b_e > c

in which b_k is the benefit to kin (b in the original equation) and b_e 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 b_e>rb_k, so that altruism needs to be explained in terms of selection at the colony level rather than at the kin level. However, kin selection and group selection are not distinct processes, and the effects of multi-level selection are already accounted for in Hamilton's rule, rb>c, provided that an expanded definition of r, not requiring Hamilton's original assumption of direct genealogical relatedness, is used, as proposed by E. O. Wilson himself.

Spatial populations of predators and prey 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 of host-parasite evolution is broadly hostile to group selection. Specifically, the parasites do not individually moderate their transmission; rather, more transmissible variants – which have a short-term but unsustainable advantage – arise, increase, and go extinct.

Applications

Differing evolutionarily stable strategies

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. But, as J. L. Mackie suggested, when there are many different groups, each with a different evolutionarily stable strategy, there is selection between the different strategies, since some are worse than others. For example, a group where altruism was universal would indeed outcompete a group where every creature acted in its own interest, so group selection might seem feasible; but a mixed group of altruists and non-altruists would be vulnerable to cheating by non-altruists within the group, so group selection would collapse.

Implications in population biology

Social behaviors such as altruism and group relationships can impact many aspects of population dynamics, such as intraspecific competition and interspecific interactions. In 1871, Darwin argued that group selection occurs when the benefits of cooperation or altruism between subpopulations are greater than the individual benefits of egotism within a subpopulation. This supports the idea of multilevel selection, but kinship also plays an integral role because many subpopulations are composed of closely related individuals. An example of this can be found in lions, which are simultaneously cooperative and territorial. Within a pride, males protect the pride from outside males, and females, who are commonly sisters, communally raise cubs and hunt. However, this cooperation seems to be density dependent. When resources are limited, group selection favors prides that work together to hunt. When prey is abundant, cooperation is no longer beneficial enough to outweigh the disadvantages of altruism, and hunting is no longer cooperative.

Interactions between different species can also be affected by multilevel selection. Predator-prey relationships can also be affected. Individuals of certain monkey species howl to warn the group of the approach of a predator. The evolution of this trait benefits the group by providing protection, but could be disadvantageous to the individual if the howling draws the predator's attention to them. By affecting these interspecific interactions, multilevel and kinship selection can change the population dynamics of an ecosystem.

Multilevel selection attempts to explain the evolution of altruistic behavior in terms of quantitative genetics. Increased frequency or fixation of altruistic alleles can be accomplished through kin selection, in which individuals engage in altruistic behavior to promote the fitness of genetically similar individuals such as siblings. However, this can lead to inbreeding depression, which typically lowers the overall fitness of a population. However, if altruism were to be selected for through an emphasis on benefit to the group as opposed to relatedness and benefit to kin, both the altruistic trait and genetic diversity could be preserved. However, relatedness should still remain a key consideration in studies of multilevel selection. Experimentally imposed multilevel selection on Japanese quail was more effective by an order of magnitude on closely related kin groups than on randomized groups of individuals.

Gene-culture coevolution in humans

Gene-culture coevolution (also called dual inheritance theory) is a modern hypothesis (applicable mostly to humans) that combines evolutionary biology and modern sociobiology to indicate group selection. 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 allows humans to develop highly distinct adaptations to the local pressures and environments more quickly than with genetic evolution alone. Robert 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 cultural evolution of behaviors and technology alongside genetic evolution. Boyd and Richerson believe that the ability to collaborate evolved during the Middle Pleistocene, a million years ago, in response to a rapidly changing climate.

In 2003, the behavioral scientist Herbert Gintis examined cultural evolution statistically, offering evidence that societies that promote pro-social norms have higher survival rates than societies that do not. Gintis wrote that genetic and cultural evolution can work together. Genes transfer information in DNA, and cultures transfer information encoded in brains, artifacts, or documents. Language, tools, lethal weapons, fire, cooking, etc., have a long-term effect on genetics. For example, cooking led to a reduction of size of the human gut, since less digestion is needed for cooked food. Language led to a change in the human larynx and an increase in brain size. Projectile weapons led to changes in human hands and shoulders, such that humans are much better at throwing objects than the closest human relative, the chimpanzee.

In 2015, William Yaworsky and colleagues surveyed the opinions of anthropologists on group selection, finding that these varied with the gender and politics of the social scientists concerned. In 2019, Howard Rachlin and colleagues proposed group selection of behavioural patterns, such as learned altruism, during ontogeny parallel to group selection during phylogeny.

Criticism

The vast majority of behavioural biologists have not been convinced by renewed attempts to revisit group selection as a plausible mechanism of evolution.

The use of the Price equation to support group selection was challenged by van Veelen in 2012, arguing that it is based on invalid mathematical assumptions.

Advocates of the gene-centered view of evolution such as Dawkins and Daniel Dennett remain unconvinced about group selection. Dawkins suggests that group selection fails to make an appropriate distinction between replicators and vehicles. The evolutionary biologist Jerry Coyne summarizes the arguments in The New York Review of Books in non-technical terms as follows:

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, little evidence exists 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 humans prosocial. These reasons explain why only a few biologists, like [David Sloan] Wilson and E. O. Wilson (no relation), advocate group selection as the evolutionary source of cooperation.

The psychologist Steven Pinker states that "group selection has no useful role to play in psychology or social science", since in these domains it "is not a precise implementation of the theory of natural selection, as it is, say, in genetic algorithms or artificial life simulations. Instead [in psychology] it is a loose metaphor, more like the struggle among kinds of tires or telephones."

Cooperation (evolution)

From Wikipedia, the free encyclopedia

https://en.wikipedia.org/wiki/Cooperation_(evolution)

In evolution, cooperation is the process where groups of organisms work or act together for common or mutual benefits. It is commonly defined as any adaptation that has evolved, at least in part, to increase the reproductive success of the actor's social partners. For example, territorial choruses by male lions discourage intruders and are likely to benefit all contributors.

This process contrasts with intragroup competition where individuals work against each other for selfish reasons. Cooperation exists not only in humans but in other animals as well. The diversity of taxa that exhibits cooperation is quite large, ranging from zebra herds to pied babblers to African elephants. Many animal and plant species cooperate with both members of their own species and with members of other species.

In animals

Cooperation in animals appears to occur mostly for direct benefit or between relatives. Spending time and resources assisting a related individual may at first seem destructive to an organism's chances of survival but is actually beneficial over the long-term. Since relatives share part of the helper's genetic make-up, enhancing each individual's chance of survival may actually increase the likelihood that the helper's genetic traits will be passed on to future generations.

However, some researchers, such as ecology professor Tim Clutton-Brock, assert that cooperation is a more complex process. They state that helpers may receive more direct, and less indirect, gains from assisting others than is commonly reported. These gains include protection from predation and increased reproductive fitness. Furthermore, they insist that cooperation may not solely be an interaction between two individuals but may be part of the broader goal of unifying populations.

Prominent biologists, such as Charles Darwin, E. O. Wilson, and W. D. Hamilton, have found the evolution of cooperation fascinating because natural selection favors those who achieve the greatest reproductive success while cooperative behavior often decreases the reproductive success of the actor (the individual performing the cooperative behavior). Hence, cooperation seemed to pose a challenging problem to the theory of natural selection, which rests on the assumption that individuals compete to survive and maximize their reproductive successes. Additionally, some species have been found to perform cooperative behaviors that may at first sight seem detrimental to their own evolutionary fitness. For example, when a ground squirrel sounds an alarm call to warn other group members of a nearby coyote, it draws attention to itself and increases its own odds of being eaten. There have been multiple hypotheses for the evolution of cooperation, all of which are rooted in Hamilton's models based on inclusive fitness. These models hypothesize that cooperation is favored by natural selection due to either direct fitness benefits (mutually beneficial cooperation) or indirect fitness benefits (altruistic cooperation). As explained below, direct benefits encompass by-product benefits and enforced reciprocity, while indirect benefits (kin selection) encompass limited dispersal, kin discrimination and the greenbeard effect.

Kin selection

One specific form of cooperation in animals is kin selection, which involves animals promoting the reproductive success of their kin, thereby promoting their own fitness.

Different theories explaining kin selection have been proposed, including the "pay-to-stay" and "territory inheritance" hypotheses. The "pay-to-stay" theory suggests that individuals help others rear offspring in order to return the favor of the breeders allowing them to live on their land. The "territory inheritance" theory contends that individuals help in order to have improved access to breeding areas once the breeders depart.

Studies conducted on red wolves support previous researchers' contention that helpers obtain both immediate and long-term gains from cooperative breeding. Researchers evaluated the consequences of red wolves' decisions to stay with their packs for extended periods of time after birth. While delayed dispersal helped other wolves' offspring, studies also found that it extended male helper wolves' life spans. This suggests that kin selection may not only benefit an individual in the long-term through increased fitness but also in the short-term through increased survival chances.

Some research suggests that individuals provide more help to closer relatives. This phenomenon is known as kin discrimination. In their meta-analysis, researchers compiled data on kin selection as mediated by genetic relatedness in 18 species, including the western bluebird, pied kingfisher, Australian magpie, and dwarf mongoose. They found that different species exhibited varying degrees of kin discrimination, with the largest frequencies occurring among those who have the most to gain from cooperative interactions.

In plants

Cooperation exists not only in animals but also in plants. In a greenhouse experiment with Ipomoea hederacea, a climbing plant, results show that kin groups have higher efficiency rates in growth than non-kin groups do. This is expected to rise out of reduced competition within the kin groups.

Explanation

The inclusive fitness theory provides a good overview of possible solutions to the fundamental problem of cooperation. The theory is based on the hypothesis that cooperation helps in transmitting underlying genes to future generations either through increasing the reproductive successes of the individual (direct fitness) or of other individuals who carry the same genes (indirect fitness). Direct benefits can result from simple by-product of cooperation or enforcement mechanisms, while indirect benefits can result from cooperation with genetically similar individuals.

Direct fitness benefits

This is also called mutually beneficial cooperation as both actor and recipient depend on direct fitness benefits, which are broken down into two different types: by-product benefit and enforcement.

By-product benefit arises as a consequence of social partners having a shared interest in cooperation. For example, in meerkats, larger group size provides a benefit to all the members of that group by increasing survival rates, foraging success and conflict wins. This is because living in groups is better than living alone, and cooperation arises passively as a result of many animals doing the same thing. By-product benefit can also arise as a consequence of subordinate animals staying and helping a nest that is dominated by leaders who often suffer high mortality rates. It has been shown that cooperation would be most advantageous for the sex that is more likely to remain and breed in the natal group. This is because the subordinate will have a higher chance to become dominant in the group as time passes. Cooperation in this scenario is often seen between non-related members of the same species, such as the wasp Polistes dominula.

Prisoner's Delight, another term to describe by-product benefit, is a term coined by Kenneth Binmore in 2007 after he found that benefits can result as an automatic consequence of an otherwise "self-interested" act in cooperative hunting. He illustrated this with a scenario having two hunters, each hunter having the choice of hunting (cooperate) or not hunting (free-riding). Assuming that cooperative hunting results in greater rewards than just a one-player hunt, when hunting is not rare, both hunters and non-hunters benefit because either player is likely to be with other hunters, and thus likely to reap the rewards of a successful hunt. This situation demonstrates "Prisoner's Delight" because the food of a successful hunt is shared between the two players regardless of whether or not they participated.

It has been shown that free riding, or reaping the benefits without any effort, is often a problem in collective action. Examples of free riding would be if an employee in a labor union pays no dues, but still benefits from union representation. In a study published in 1995, scientists found that female lions showed individual differences in the extent to which they participated in group-territorial conflict. Some lions consistently 'cooperated' by approaching intruders, while others 'lagged' behind to avoid the risk of fighting. Although the lead female recognized the laggards, she failed to punish them, suggesting that cooperation is not maintained by reciprocity.

Cooperation is maintained in situations where free-riding is a problem through enforcement, which is the mechanism where the actor is rewarded for cooperating or punished for not cooperating. This happens when cooperation is favored in aiding those who have helped the actors in the past. Punishment for noncooperation has been documented in meerkats, where dominant females will attack and evict subordinate females who become pregnant. The pregnancy is seen as a failure to cooperate because only the dominant females are allowed to bear offspring. Dominant females will attack and kill the offspring of subordinate females if they evade eviction and eviction often leads to increased stress and decreased survival.

Enforcement can also be mutually beneficial, and is often called reciprocal cooperation because the act of cooperation is preferentially directed at individuals who have helped the actor in the past (directly), or helped those who have helped the actor in the past (indirectly).

Indirect fitness benefits

The second class of explanations for cooperation is indirect fitness benefits, or altruistic cooperation. There are three major mechanisms that generate this type of fitness benefit: limited dispersal, kin discrimination and the green-beard effect.

Hamilton originally suggested that high relatedness could arise in two ways: direct kin recognition between individuals or limited dispersal, or population viscosity, which can keep relatives together. The easiest way to generate relatedness between social partners is limited dispersal, a mechanism in which genetic similarity correlates with spatial proximity. If individuals do not move far, then kin usually surrounds them. Hence, any act of altruism would be directed primarily towards kin. This mechanism has been shown in Pseudomonas aeruginosa bacteria, where cooperation is disfavored when populations are well mixed, but favored when there is high local relatedness.

Kin discrimination also influences cooperation because the actor can give aid preferentially towards related partners. Since kin usually share common genes, it is thought that this nepotism can lead to genetic relatedness between the actor and the partner's offspring, which affects the cooperation an actor might give.

This mechanism is similar to what happens with the green-beard effect, but with the green-beard effect, the actor has to instead identify which of its social partners share the gene for cooperation. A green-beard system must always co-occur within individuals and alleles to produce a perceptible trait, recognition of this trait in others, and preferential treatment to those recognized. Examples of green-beard behavior have been found in hydrozoans, slime molds, yeast, and ants. An example is in side-blotch lizards, where blue-throated males preferentially establish territories next to each other. Results show that neighboring blue-throats are more successful at mate guarding. However, blue males next to larger, more aggressive orange males suffer a cost. This strategy blue has evolutionary cycles of altruism alternating with mutualism tied to the RPS game.

Multi-level selection

Multi-level selection theory suggests that selection operates on more than one level: for example, it may operate at an atomic and molecular level in cells, at the level of cells in the body, and then again at the whole organism level, and the community level, and the species level. Any level which is not competitive with others of the same level will be eliminated, even if the level below is highly competitive. A classic example is that of genes which prevent cancer. Cancer cells divide uncontrollably, and at the cellular level, they are very successful, because they are (in the short term) reproducing very well and out competing other cells in the body. However, at the whole organism level, cancer is often fatal, and so may prevent reproduction. Therefore, changes to the genome which prevent cancer (for example, by causing damaged cells to act co-operatively by destroying themselves) are favoured. Multi-level selection theory contends that similar effects can occur, for example, to cause individuals to co-operate to avoid behaviours which favour themselves short-term, but destroy the community (and their descendants) long term.

Market effect

One theory suggesting a mechanism that could lead to the evolution of co-operation is the "market effect" as suggested by Noe and Hammerstein. The mechanism relies on the fact that in many situations there exists a trade-off between efficiency obtaining a desired resource and the amount of resources one can actively obtain. In that case, each partner in a system could benefit from specializing in producing one specific resource and obtaining the other resource by trade. When only two partners exist, each can specialize in one resource, and trade for the other. Trading for the resource requires co-operation with the other partner and includes a process of bidding and bargaining.

This mechanism can be relied to both within a species or social group and within species systems. It can also be applied to a multi-partner system, in which the owner of a resource has the power to choose its co-operation partner. This model can be applied in natural systems (examples exist in the world of apes, cleaner fish, and more). Easy for exemplifying, though, are systems from international trading. Arabic countries control vast amounts of oil, but seek technologies from western countries. These in turn are in need of Arab oil. The solution is co-operation by trade.

Symbiosis

Symbiosis refers to two or more biological species that interact closely, often over a long period of time. Symbiosis includes three types of interactions—mutualism, commensalism, and parasitism—of which only mutualism can sometimes qualify as cooperation. Mutualism involves a close, mutually beneficial interaction between two different biological species, whereas "cooperation" is a more general term that can involve looser interactions and can be interspecific (between species) or intraspecific (within a species). In commensalism, one of the two participating species benefits, while the other is neither harmed nor benefitted. In parasitism, one of the two participating species benefits at the expense of the other.

Symbiosis may be obligate or facultative. In obligate symbiosis, one or both species depends on the other for survival. In facultative symbiosis, the symbiotic interaction is not necessary for the survival of either species.

Two special types of symbiosis include endosymbiosis, in which one species lives inside of another, and ectosymbiosis, in which one species lives on another.

Mutualism

Mutualism is a form of symbiosis in which both participating species benefit.

A classic example of mutualism is the interaction between rhizobia soil bacteria and legumes (Fabaceae). In this interaction, rhizobia bacteria induce root nodule formation in legume plants via an exchange of molecular signals. Within the root nodules, rhizobia fix atmospheric nitrogen into ammonia using the nitrogenase enzyme. The legume benefits from a new supply of usable nitrogen from the rhizobia, and the rhizobia benefits from organic acid energy sources from the plant as well as the protection provided by the root nodule. Since the rhizobia live within the legume, this is an example of endosymbiosis, and since both the bacteria and the plant can survive independently, it is also an example of facultative symbiosis.

Lichens are another example of mutualism. Lichens consist of a fungus (the mycobiont) and a photosynthetic partner (the photobiont), which is usually a green alga or a cyanobacteria. The mycobiont benefits from the sugar products of photosynthesis generated by the photobiont, and the photobiont benefits from the increased water retention and increased surface area to capture water and mineral nutrients conferred by the mycobiont. Many lichens are examples of obligate symbiosis. In fact, one-fifth of all known extant fungal species form obligate symbiotic associations with green algae, cyanobacteria or both.

Not all examples of mutualism are also examples of cooperation. Specifically, in by-product mutualism, both participants benefit, but cooperation is not involved. For example, when an elephant defecates, this is beneficial to the elephant as a way to empty waste, and it is also beneficial to a dung beetle that uses the elephant's dung. However, neither participant's behavior yields a benefit from the other, and thus cooperation is not taking place.

Hidden benefits

Hidden benefits are benefits from cooperation that are not obvious because they are obscure or delayed. (For example, a hidden benefit would not involve an increase in the number of offspring or offspring viability.)

One example of a hidden benefit involves Malarus cyaneus, the superb fairy-wren. In M. cyaneus, the presence of helpers at the nest does not lead to an increase in chick mass. However, the presence of helpers does confer a hidden benefit: it increases the chance that a mother will survive to breed in the next year.

Another example of a hidden benefit is indirect reciprocity, in which a donor individual helps a beneficiary to increase the probability that observers will invest in the donor in the future, even when the donor will have no further interaction with the beneficiary.

In a study of 79 students, participants played a game in which they could repeatedly give money to others and receive from others. They were told that they would never interact with the same person in the reciprocal role. A player's history of donating was displayed at each anonymous interaction, and donations were significantly more frequent to receivers who had been generous to others in earlier interactions. Indirect reciprocity has only been shown to occur in humans.

Prisoner's dilemma

Even if all members of a group benefit from cooperation, individual self-interest may not favor cooperation. The prisoner's dilemma codifies this problem and has been the subject of much research, both theoretical and experimental. In its original form the prisoner's dilemma game (PDG) described two awaiting trial prisoners, A and B, each faced with the choice of betraying the other or remaining silent. The "game" has four possible outcomes: (a) they both betray each other, and are both sentenced to two years in prison; (b) A betrays B, which sets A free and B is sentenced to four years in prison; (c) B betrays A, with the same result as (b) except that it is B who is set free and the other spends four years in jail; (d) both remain silent, resulting in a six-month sentence each. Clearly (d) ("cooperation") is the best mutual strategy, but from the point of view of the individual betrayal is unbeatable (resulting in being set free, or getting only a two-year sentence). Remaining silent results in a four-year or six-month sentence. This is exemplified by a further example of the PDG: two strangers attend a restaurant together and decide to split the bill. The mutually best ploy would be for both parties to order the cheapest items on the menu (mutual cooperation). But if one member of the party exploits the situation by ordering the most expensive items, then it is best for the other member to do likewise. In fact, if the fellow diner's personality is completely unknown, and the two diners are unlikely ever to meet again, it is always in one's own best interests to eat as expensively as possible. Situations in nature that are subject to the same dynamics (rewards and penalties) as the PDG define cooperative behavior: it is never in the individual's fitness interests to cooperate, even though mutual cooperation rewards the two contestants (together) more highly than any other strategy. As described in the Nash equilibrium, cooperation cannot evolve under these circumstances.

However, in 1981 Axelrod and Hamilton noted that if the same contestants in the PDG meet repeatedly (in the so-called iterated prisoner's dilemma game, IPD) then tit-for-tat (foreshadowed by Robert Trivers' 1971 reciprocal altruism theory) is a robust strategy which promotes altruism. In "tit-for-tat" both players' opening moves are cooperation. Thereafter each contestant repeats the other player's last move, resulting in a seemingly endless sequence of mutually cooperative moves. However, mistakes severely undermine tit-for-tat's effectiveness, giving rise to prolonged sequences of betrayal, which can only be rectified by another mistake. Since these initial discoveries, all the other possible IPD game strategies have been identified (16 possibilities in all, including, for instance, "generous tit-for-tat", which behaves like "tit-for-tat", except that it cooperates with a small probability when the opponent's last move was "betray".), but all can be outperformed by at least one of the other strategies, should one of the players switch to such a strategy. The result is that none is evolutionarily stable, and any prolonged series of the iterated prisoner's dilemma game, in which alternative strategies arise at random, gives rise to a chaotic sequence of strategy changes that never ends.

Results from experimental economics show, however, that humans often act more cooperatively than strict self-interest would dictate.

Evolutionary mechanisms suggesting that reciprocity is the result, not the cause, of the evolution of cooperation

In the light of the iterated prisoner's dilemma game and the reciprocal altruism theory failing to provide full answers to the evolutionary stability of cooperation, several alternative explanations have been proposed.

A male peacock with its beautiful but clumsy, aerodynamically unsound erectile tail, which Amotz Zahavi believes is a handicap, comparable to a race horse's handicap. The larger the handicap the more intrinsically fit the individual (see text).

There are striking parallels between cooperative behavior and exaggerated sexual ornaments displayed by some animals, particularly certain birds, such as, amongst others, the peacock. Both are costly in fitness terms, and both are generally conspicuous to other members of the population or species. This led Amotz Zahavi to suggest that both might be fitness signals rendered evolutionarily stable by his handicap principle. If a signal is to remain reliable, and generally resistant to falsification, the signal has to be evolutionarily costly. Thus, if a (low fitness) liar were to use the highly costly signal, which seriously eroded its real fitness, it would find it difficult to maintain a semblance or normality. Zahavi borrowed the term "handicap principle" from sports handicapping systems. These systems are aimed at reducing disparities in performance, thereby making the outcome of contests less predictable. In a horse handicap race, provenly faster horses are given heavier weights to carry under their saddles than inherently slower horses. Similarly, in amateur golf, better golfers have fewer strokes subtracted from their raw scores than the less talented players. The handicap therefore correlates with unhandicapped performance, making it possible, if one knows nothing about the horses, to predict which unhandicapped horse would win an open race. It would be the one handicapped with the greatest weight in the saddle. The handicaps in nature are highly visible, and therefore a peahen, for instance, would be able to deduce the health of a potential mate by comparing its handicap (the size of the peacock's tail) with those of the other males. The loss of the male's fitness caused by the handicap is offset by his increased access to females, which is as much of a fitness concern as is his health. A cooperative act is, by definition, similarly costly (e.g. helping raise the young at the nest of an unrelated pair of birds versus producing and raising one's own offspring). It would therefore also signal fitness, and is probably as attractive to females as a physical handicap. If this is the case, cooperation is evolutionarily stabilized by sexual selection.

There is an alternate strategy for identifying fit mates which does not rely on one gender having exaggerated sexual ornaments or other handicaps, but is probably generally applicable to most, if not all sexual creatures. It derives from the concept that the change in appearance and functionality caused by a non-silent mutation will generally stand out in a population. This is because that altered appearance and functionality will be unusual, peculiar, and different from the norm within that population. The norm against which these unusual features are judged is made up of fit attributes that have attained their plurality through natural selection, while less well adapted attributes will be in the minority or frankly rare. Since the overwhelming majority of mutant features are maladaptive, and it is impossible to predict evolution's future direction, sexual creatures would be expected to prefer mates with the fewest unusual or minority features. This will have the effect of a sexual population rapidly shedding peripheral phenotypic features, thereby canalizing the entire outward appearance and behavior of all of its members. They will all very quickly begin to look remarkably similar to one another in every detail, as illustrated in the accompanying photograph of the African pygmy kingfisher, Ispidina picta. Once a population has become as homogeneous in appearance as is typical of most species, its entire repertoire of behaviors will also be rendered evolutionarily stable, including any cooperative, altruistic and social interactions. Thus, in the example above of the selfish individual who hangs back from the rest of the hunting pack, but who nevertheless joins in the spoils, that individual will be recognized as being different from the norm, and will therefore find it difficult to attract a mate (koinophilia). Its genes will therefore have only a very small probability of being passed on to the next generation, thus evolutionarily stabilizing cooperation and social interactions at whatever level of complexity is the norm in that population.

History of cooperation research

One of the first references to animal cooperation was made by Charles Darwin, who noted it as a potential problem for his theory of natural selection. In most of the 19th century, intellectuals like Thomas Henry Huxley and Peter Kropotkin debated fervently on whether animals cooperate with one another and whether animals displayed altruistic behaviors.

In the late 1900s, some early research in animal cooperation focused on the benefits of group-living. While living in a group produces costs in the form of increased frequency of predator attacks and greater mating competition, some animals find that the benefits outweigh the costs. Animals that practice group-living often benefit from assistance in parasite removal, access to more mates, and conservation of energy in foraging. Initially, the most obvious form of animal cooperation was kin selection, but more recent studies focus on non-kin cooperation, where benefits may seem less obvious. Non-kin cooperation often involves many strategies that include manipulation and coercion, making these interactions more complicated to study. An example of manipulation is presented by the cuckoo, a brood parasite, which lays its eggs in the nest of a bird of another species. That bird then is tricked into feeding and caring for the cuckoo offspring. Although this phenomenon may look like cooperation at first glance, it only presents benefits to one recipient.

In the past, simple game theory models, such as the classic cooperative hunting and Prisoner's dilemma models, were used to determine decisions made by animals in cooperative relationships. However, complicated interactions between animals have required the use of more complex economic models such as the Nash equilibrium. The Nash equilibrium is a type of non-cooperative game theory that assumes an individual's decision is influenced by its knowledge of the strategies of other individuals. This theory was novel because it took into consideration the higher cognitive capabilities of animals. The evolutionarily stable strategy is a refined version of the Nash equilibrium in that it assumes strategies are heritable and are subject to natural selection. Economic models are useful for analyzing cooperative relationships because they provide predictions on how individuals act when cooperation is an option. Economic models are not perfect, but they provide a general idea of how cooperative relationships work.

Contrary to the mainstream dogma, a recently published article. using agent-based models demonstrates that several crucial mechanisms, such as kin selection, punishment, multilevel selection, and spatial structure, cannot rescue the evolution of cooperation. The new findings revive a long-standing puzzle in the evolution theory. In addition, the work has potential therapeutic benefits for numerous incurable diseases.

Altruism

From Wikipedia, the free encyclopedia
https://en.wikipedia.org/wiki/Altruism_(biology)

In biology, altruism refers to behaviour by an individual that increases the fitness of another individual while decreasing their own. Altruism in this sense is different from the philosophical concept of altruism, in which an action would only be called "altruistic" if it was done with the conscious intention of helping another. In the behavioural sense, there is no such requirement. As such, it is not evaluated in moral terms—it is the consequences of an action for reproductive fitness that determine whether the action is considered altruistic, not the intentions, if any, with which the action is performed.

The term altruism was coined by the French philosopher Auguste Comte in French, as altruisme, for an antonym of egoism. He derived it from the Italian altrui, which in turn was derived from Latin alteri, meaning "other people" or "somebody else".

Altruistic behaviours appear most obviously in kin relationships, such as in parenting, but may also be evident among wider social groups, such as in social insects. They allow an individual to increase the success of its genes by helping relatives that share those genes. Obligate altruism is the permanent loss of direct fitness (with potential for indirect fitness gain). For example, honey bee workers may forage for the colony. Facultative altruism is temporary loss of direct fitness (with potential for indirect fitness gain followed by personal reproduction). For example, a Florida scrub jay may help at the nest, then gain parental territory.

Overview

In ethology (the study of behavior), and more generally in the study of social evolution, on occasion, some animals do behave in ways that reduce their individual fitness but increase the fitness of other individuals in the population; this is a functional definition of altruism. Research in evolutionary theory has been applied to social behaviour, including altruism. Cases of animals helping individuals to whom they are closely related can be explained by kin selection, and are not considered true altruism. Beyond the physical exertions that in some species mothers and in some species fathers undertake to protect their young, extreme examples of sacrifice may occur. One example is matriphagy (the consumption of the mother by her offspring) in the spider Stegodyphus; another example is a male spider allowing a female fertilized by him to eat him. Hamilton's rule describes the benefit of such altruism in terms of Wright's coefficient of relationship to the beneficiary and the benefit granted to the beneficiary minus the cost to the sacrificer. Should this sum be greater than zero a fitness gain will result from the sacrifice.

When apparent altruism is not between kin, it may be based on reciprocity. A monkey will present its back to another monkey, who will pick out parasites; after a time the roles will be reversed. Such reciprocity will pay off, in evolutionary terms, as long as the costs of helping are less than the benefits of being helped and as long as animals will not gain in the long run by "cheating"—that is to say, by receiving favours without returning them. This is elaborated on in evolutionary game theory and specifically the prisoner's dilemma as social theory.

Implications in evolutionary theory

The existence of altruism in nature is at first sight puzzling, because altruistic behaviour reduces the likelihood that an individual will reproduce. The idea that group selection might explain the evolution of altruism was first broached by Darwin himself in The Descent of Man, and Selection in Relation to Sex, (1871). The concept of group selection has had a chequered and controversial history in evolutionary biology but the uncritical 'good of the species' tradition came to an abrupt halt in the 1960s, due largely to the work of George C. Williams, and John Maynard Smith as well as Richard Dawkins.These evolutionary theorists pointed out that natural selection acts on the individual, and that it is the individual's fitness (number of offspring and grand-offspring produced compared to the rest of the population) that drives evolution. A group advantage (e.g. hunting in a pack) that is disadvantageous to the individual (who might be harmed during the hunt, when it could avoid injury by hanging back from the pack but still share in the spoils) cannot evolve, because the selfish individual will leave, on average, more offspring than those who join the pack and suffer injuries as a result. If the selfishness is hereditary, this will ultimately result in the population consisting entirely of selfish individuals. However, in the 1960s and 1970s an alternative to the "group selection" theory emerged. This was the kin selection theory, due originally to W. D. Hamilton. Kin selection is an instance of inclusive fitness, which is based on the notion that an individual shares only half its genes with each offspring, but also with each full sibling (See footnote). From an evolutionary genetic point of view it is therefore as advantageous to help with the upbringing of full sibs as it is to produce and raise one's own offspring. The two activities are evolutionarily entirely equivalent. Co-operative breeding (i.e. helping one's parents raise sibs—provided they are full sibs) could thus evolve without the need for group-level selection. This quickly gained prominence among biologists interested in the evolution of social behaviour.

In 1971 Robert Trivers introduced his reciprocal altruism theory to explain the evolution of helping at the nest of an unrelated breeding pair of birds. He argued that an individual might act as a helper if there was a high probabilistic expectation of being helped by the recipients at some later date. If, however, the recipients did not reciprocate when it was possible to do so, the altruistic interaction with these recipients would be permanently terminated. But if the recipients did not cheat then the reciprocal altruism would continue indefinitely to both parties' advantage. This model was considered by many (e.g. West-Eberhard and Dawkins) to be evolutionarily unstable because it is prone to invasion by cheats for the same reason that cooperative hunting can be invaded and replaced by cheats. However, Trivers did make reference to the Prisoner's Dilemma Game which, 10 years later, would restore interest in Trivers' reciprocal altruism theory, but under the title of "tit-for-tat".

In its original form the Prisoner's Dilemma Game (PDG) described two awaiting trial prisoners, A and B, each faced with the choice of betraying the other or remaining silent. The "game" has four possible outcomes: (a) they both betray each other, and are both sentenced to two years in prison; (b) A betrays B, which sets A free and B is sentenced to four years in prison; (c) B betrays A, with the same result as (b) except that it is B who is set free and the other spends four years in jail; (d) both remain silent, resulting in a six-month sentence each. Clearly (d) ("cooperation") is the best mutual strategy, but from the point of view of the individual betrayal is unbeatable (resulting in being set free, or getting only a two-year sentence). Remaining silent results in a four-year or six-month sentence. This is exemplified by a further example of the PDG: two strangers attend a restaurant together and decide to split the bill. The mutually best ploy would be for both parties to order the cheapest items on the menu (mutual cooperation). But if one member of the party exploits the situation by ordering the most expensive items, then it is best for the other member to do likewise. In fact, if the fellow diner's personality is completely unknown, and the two diners are unlikely ever to meet again, it is always in one's own best interests to eat as expensively as possible. Situations in nature that are subject to the same dynamics (rewards and penalties) as the PDG define cooperative behaviour: it is never in the individual's fitness interests to cooperate, even though mutual cooperation rewards the two contestants (together) more highly than any other strategy. Cooperation cannot evolve under these circumstances.

However, in 1981 Axelrod and Hamilton noted that if the same contestants in the PDG meet repeatedly (the so-called Iterated Prisoner's Dilemma game, IPD) then tit-for-tat (foreshadowed by Robert Triver's reciprocal altruism theory) is a robust strategy which promotes altruism. In "tit-for-tat" both players' opening moves are cooperation. Thereafter each contestant repeats the other player's last move, resulting in a seemingly endless sequence of mutually cooperative moves. However, mistakes severely undermine tit-for-tat's effectiveness, giving rise to prolonged sequences of betrayal, which can only be rectified by another mistake. Since these initial discoveries, all the other possible IPD game strategies have been identified (16 possibilities in all, including, for instance, "generous tit-for-tat", which behaves like "tit-for-tat", except that it cooperates with a small probability when the opponent's last move was "betray".), but all can be outperformed by at least one of the other strategies, should one of the players switch to such a strategy. The result is that none is evolutionarily stable, and any prolonged series of the iterated prisoner's dilemma game, in which alternative strategies arise at random, gives rise to a chaotic sequence of strategy changes that never ends.

The handicap principle

A male peacock with its beautiful but clumsy, aerodynamically unsound tail—a handicap, comparable to a race horse's handicap.

The best horses in a handicap race carry the largest weights, so the size of the handicap is a measure of the animal's quality

In the light of the Iterated Prisoner's Dilemma Game failing to provide a full answer to the evolution of cooperation or altruism, several alternative explanations have been proposed.

There are striking parallels between altruistic acts and exaggerated sexual ornaments displayed by some animals, particularly certain bird species, such as, amongst others, the peacock. Both are costly in fitness terms, and both are generally conspicuous to other members of the population or species. This led Amotz Zahavi to suggest that both might be fitness signals rendered evolutionarily stable by his handicap principle. If a signal is to remain reliable, and generally resistant to falsification, the signal has to be evolutionarily costly. Thus, if a (low fitness) liar were to use the highly costly signal, which seriously eroded its real fitness, it would find it difficult to maintain a semblance of normality. Zahavi borrowed the term "handicap principle" from sports handicapping systems. These systems are aimed at reducing disparities in performance, thereby making the outcome of contests less predictable. In a horse handicap race, provenly faster horses are given heavier weights to carry under their saddles than inherently slower horses. Similarly, in amateur golf, better golfers have fewer strokes subtracted from their raw scores than the less talented players. The handicap therefore correlates with unhandicapped performance, making it possible, if one knows nothing about the horses, to predict which unhandicapped horse would win an open race. It would be the one handicapped with the greatest weight in the saddle. The handicaps in nature are highly visible, and therefore a peahen, for instance, would be able to deduce the health of a potential mate by comparing its handicap (the size of the peacock's tail) with those of the other males. The loss of the male's fitness caused by the handicap is offset by its increased access to females, which is as much of a fitness concern as is its health. An altruistic act is, by definition, similarly costly. It would therefore also signal fitness, and is probably as attractive to females as a physical handicap. If this is the case altruism is evolutionarily stabilized by sexual selection.

There is an alternate strategy for identifying fit mates which does not rely on one gender having exaggerated sexual ornaments or other handicaps, but is generally applicable to most, if not all sexual creatures. It derives from the concept that the change in appearance and functionality caused by a non-silent mutation will generally stand out in a population. This is because that altered appearance and functionality will be unusual, peculiar, and different from the norm within that population. The norm against which these unusual features are judged is made up of fit attributes that have attained their plurality through natural selection, while less adaptive attributes will be in the minority or frankly rare. Since the overwhelming majority of mutant features are maladaptive, and it is impossible to predict evolution's future direction, sexual creatures would be expected to prefer mates with the fewest unusual or minority features.This will have the effect of a sexual population rapidly shedding peripheral phenotypic features and canalizing the entire outward appearance and behaviour so that all the members of that population will begin to look remarkably similar in every detail, as illustrated in the accompanying photograph of the African pygmy kingfisher, Ispidina picta. Once a population has become as homogeneous in appearance as is typical of most species, its entire repertoire of behaviours will also be rendered evolutionarily stable, including any altruistic, cooperative and social characteristics. Thus, in the example of the selfish individual who hangs back from the rest of the hunting pack, but who nevertheless joins in the spoils, that individual will be recognized as being different from the norm, and will therefore find it difficult to attract a mate. Its genes will therefore have only a very small probability of being passed on to the next generation, thus evolutionarily stabilizing cooperation and social interactions at whatever level of complexity is the norm in that population.

Contrary to the mainstream dogma, a recently published article using agent-based models demonstrates that several crucial mechanisms, such as kin selection, punishment, multilevel selection, and spatial structure, cannot rescue the evolution of cooperation. The new findings revive a long-standing puzzle in the evolution theory. In addition, the work has potential therapeutic benefits for numerous incurable diseases

Reciprocity mechanisms

Altruism in animals describes a range of behaviors performed by animals that may be to their own disadvantage but which benefit others. The costs and benefits are measured in terms of reproductive fitness, or expected number of offspring. So by behaving altruistically, an organism reduces the number of offspring it is likely to produce itself, but boosts the likelihood that other organisms are to produce offspring. There are other forms of altruism in nature other than risk-taking behavior, such as reciprocal altruism. This biological notion of altruism is not identical to the everyday human concept. For humans, an action would only be called 'altruistic' if it was done with the conscious intention of helping another. Yet in the biological sense there is no such requirement. Instead, until we can communicate directly with other species, an accurate theory to describe altruistic acts between species is Biological Market Theory. Humans and other animals exchange benefits in several ways, known technically as reciprocity mechanism. No matter what the mechanism, the common thread is that benefits find their way back to the original giver.

Symmetry-based

Also known as the "buddy-system", mutual affection between two parties prompts similar behavior in both directions without need to track of daily give-and-take, so long as the overall relationship remains satisfactory. This is one of the most common mechanisms of reciprocity in nature, this kind is present in humans, primates, and many other mammals.

Attitudinal

Also known as, "If you're nice, I'll be nice too." This mechanism of reciprocity is similar to the heuristic of the golden rule, "Treat others how you would like to be treated." Parties mirror one another's attitudes, exchanging favors on the spot. Instant attitudinal reciprocity occurs among monkeys, and people often rely on it with strangers and acquaintances.

Calculated

Also known as, "what have you done for me lately?" Individuals keep track of the benefits they exchange with particular partners, which helps them decide to whom to return favors. This mechanism is typical of chimpanzees and very common among human relationships. Yet some opposing experimental research suggests that calculated or contingent reciprocity does not spontaneously arise in laboratory experimental settings, despite patterns of behavior.

Biological market theory

Biological market theory is an extension of the idea of reciprocal altruism, as a mechanism to explain altruistic acts between unrelated individuals in a more flexible system of exchanging commodities. The term 'biological market' was first used by Ronald Noe and Hammerstein in 1994 to refer to all the interactions between organisms in which different organisms function as 'traders' that exchange goods and services such as food and water, grooming, warning calls, shelter, etc. Biological market theory consists of five formal characteristics which present a basis for altruism.

Commodities are exchanged between individuals that differ in the degree of control over those commodities.
Trading partners are chosen from a number of potential partners.
There is competition among the members of the chosen class to be the most attractive partner. This competition by 'outbidding' causes an increase in the value of the commodity offered.
Supply and demand determine the bartering value of commodities exchanged.
Commodities on offer can be advertised. As in commercial advertisements there is a potential for false information.

The applicability of biological market theory with its emphasis on partner choice is evident in the interactions between the cleaner wrasse and its "client" reef fish. Cleaners have small territories, which the majority of reef fish species actively visit to invite inspection of their surface, gills, and mouth. Clients benefit from the removal of parasites while cleaners benefit from the access to a food source. Some particularly choosy client species have large home ranges that cover several cleaning stations, whereas other clients have small ranges and have access to one cleaning station only (resident clients). Field observations, field manipulations, and laboratory experiments revealed that whether or not a client has choice options influences several aspects of both cleaner and client behaviour. Cleaners give choosy clients priority of access. Choosy clients switch partners if cheated by a cleaner by taking a bite of out of the cleaner, whereas resident clients punish cheats. Cleaners and resident clients, but not choosy clients, build up relationships before normal cleaning interactions take place. Cleaners are particularly cooperative if choosy clients are bystanders of an interaction but less so when resident clients are bystanders.

Researchers tested whether wild white-handed gibbon males from Khao Yai National Park, Thailand, increased their grooming activity when the female partner was fertile. Adult females and males of our study population are codominant (in terms of aggression), they live in pairs or small multi male groups and mate promiscuously. They found that males groomed females more than vice versa and more grooming was exchanged when females were cycling than during pregnancy or lactation. The number of copulations/day was elevated when females were cycling, and females copulated more frequently with males on days when they received more grooming. When males increased their grooming efforts, females also increased their grooming of males, perhaps to equalize give and take. Although grooming might be reciprocated because of intrinsic benefits of receiving grooming, males also interchange grooming as a commodity for sexual opportunities during a female's fertile period.

Examples in vertebrates

Mammals

Wolves and wild dogs bring meat back to members of the pack not present at the kill. Though in harsh conditions, the breeding pair of wolves take the greatest share to continue to produce pups.
Mongooses support elderly, sick, or injured animals.
Meerkats often have one standing guard to warn while the rest feed in case of predator attack.
Raccoons inform conspecifics about feeding grounds by droppings left on commonly shared latrines. A similar information system has been observed to be used by common ravens.
Male baboons threaten predators and cover the rear as the troop retreats.
Gibbons and chimpanzees with food will, in response to a gesture, share their food with others of the group. Chimpanzees will help humans and conspecifics without any reward in return.
Bonobos have been observed aiding injured or disabled bonobos.
Vampire bats commonly regurgitate blood to share with unlucky or sick roost mates that have been unable to find a meal, often forming a buddy system.
Vervet monkeys give alarm calls to warn fellow monkeys of the presence of predators, even though in doing so they attract attention to themselves, increasing their personal chance of being attacked.
Lemurs of all ages and of both sexes will take care of infants unrelated to them.
Dolphins support sick or injured members of their pod, swimming under them for hours at a time and pushing them to the surface so they can breathe.
Walruses have been seen adopting orphans who lost their parents to predators.
African buffalo will rescue a member of the herd captured by predators. (See Battle at Kruger.)
Humpback whales have been observed protecting other species from killer whales.
Male Przewalski's horses have been observed engaging in intervention behaviour when their group members were threatened. They did not distinguish between kin and non-kin members. It has been theorized that they may do this to promote group cohesion and reduce social disruption within the group.

Birds

In numerous bird species, a breeding pair receives support in raising its young from other "helper" birds, including help with the feeding of its fledglings. Some will even go as far as protecting an unrelated bird's young from predators.

Fish

Harpagifer bispinis, a species of fish, live in social groups in the harsh environment of the Antarctic Peninsula. If the parent guarding the nest of eggs is removed, a usually male replacement unrelated to the parents guards the nest from predators and prevents fungal growth that would kill off the brood. There is no clear benefit to the male so the act may be considered altruistic.

Examples in invertebrates

Some termites, such as Globitermes sulphureus and ants, such as Camponotus saundersi release a sticky secretion by fatally rupturing a specialized gland. This autothysis altruistically defends the colony at the expense of the individual insect. This can be attributed to the fact that ants share their genes with the entire colony, and so this behaviour is evolutionarily beneficial (not necessarily for the individual ant but for the continuation of its genetic make-up).
Synalpheus regalis is a species of eusocial marine snapping shrimp that lives in sponges in coral reefs. They live in colonies of about 300 individuals with one reproductive female. Other colony members defend the colony against intruders, forage, and care for the young. Eusociality in this system entails an adaptive division of labor which results in enhanced reproductive output of the breeders and inclusive fitness benefits for the nonbreeding helpers. S. regalis are exceptionally tolerant of conspecifics within their colonies due to close genetic relatedness among nestmates. Allozyme data reveals that relatedness within colonies is high, which is an indication that colonies in this species represent close kin groups. The existence of such groups is an important prerequisite of explanations of social evolution based on kin selection.

Examples in protists

An example of altruism is found in the cellular slime moulds, such as Dictyostelium mucoroides. These protists live as individual amoebae until starved, at which point they aggregate and form a multicellular fruiting body in which some cells sacrifice themselves to promote the survival of other cells in the fruiting body.

Examples in plants

When it comes to altruism in kin/non-kin recognition, few studies have focused on this trait in crops. Despite most crops growing in monocultures, there is evidence that they are able to recognize kin and other cultivars. For example, cultivated soybean plants were able to recognize a distant ancestor and unrelated neighbors. In that experiment, plants were grown in combinations of relation to each other (same cultivar or different cultivar) in pots and their biomass of stems, leaves, and roots were measured to see how the plants responded growing next to kin or non-kin. Crops, unlike wild plants, are highly cultivated. The evolution of traits such as altruism can thus be bred into them through the selection of the trait. In agriculture, the importance of yield is stressed, therefore breeding crop cultivars to favor altruism can decrease competitiveness and increase yield. It has been shown that using mass selection early in the breeding process selects against altruism in an individual, but using mixed individual and group selection favors altruism.

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