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 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. ==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. ==See also== ==Notes==

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