The prisoner's dilemma revisited
Remember that in the prisoner's dilemma, the two interactants are faced with the prospect of getting more of a reward if both cooperate than if neither cooperates. However, the biggest reward comes when you lure your opponent into cooperating while you defect. The cooperation and defection take place in the same turn, and in subsequent turns the players have the opportunity to punish or reward their opponent.
Another way of playing the game is to consider future pay-offs when making a play. An animal may cooperate, even if the other defects on the current move, if it anticipates that in the future its opponent will cooperate. This is called reciprocal altruism. The problem, of course, is that there may be no way to enforce the reciprocity; the opponent may fail to reciprocate. Considerable theoretical and empirical work has attempted to determine whether reciprocal altruism exists in nature.
Are there other ways of explaining apparently cooperative behavior? One school of thought argues that all behavior is selfish, and that deep enough analysis will uncover the reward an animal receives for apparently altruistic behavior. Hardest to explain from pure selfish points of view are accounts, anecdotal but reliable, of cross-species helping behavior, such as dolphins rescuing humans from **. More scientific work needs to be done to unravel the mystery of cooperative behavior.
Cooperation among non-kin
I have discussed the major contexts for cooperation among non-kin in other chapters. Here are links to those discussions:
Dominance hierarchies in social groups
Dominance hierarchies are an important form of communication within groups of animals. They establish priority of access to resources and, as long as animals behave consistently with their status, the hiearchy reduces the level of overt conflict within the group. Dominance hierarchies facilitate group living, and consequently are the basis of important forms of cooperation.
The best known dominance hiearchies, such as those in flocks of domestic hens, are linear, meaning that each individual's rank can be determined by observation. In addition to hens, dominance hiearchies are known in various primates, in herds of ungulates, and in cockoaches.
Cooperation among kin, kin selection and kin recognitionW. D. Hamilton's theory of kin selection, published in 1964, reshaped how biologists think of animal behavior. His theory caused biologists to see that familial relationships are a critical element of animal behavior. This, in turn, led to the application of molecular technology in animal behavior studies. Kinship is a key element of most contemporary field studies of social behavior in animals. An animal has two ways of gaining fitness. The first, and obvious, is to reproduce. The second is less obvious; an animal can gain fitness by aiding close relatives. This is kin selection. Close relatives share genes (have genes that are identical by descent). In fact, if a relative's reproduction is increased enough, it may even benefit an animal to behave in ways that reduce its own reproduction. In the extreme case of the eusocial insects (termites, ants, bees, wasps, and a few other types of insect) workers give up their reproduction to assist their mother in raising her offspring.
For kin selection animals usually need to be able to discriminate kin from non-kin. Kin recognition can create "structured demes" in which kin are positively associated by helping dynamics and negatively associated by mating dynamics. If a deme is structured, then there are effects on a variety of population processes at the genetic and behavioral levels.
Recognition works on several levels: Species recognition, sexual recognition, social group recognition, individual recognition, or kin recognition. Kin recognition has the special property of being generalizable to previously unmet individuals; an animal that is unfamiliar can still be discriminated as kin or non-kin. This may be particularly important in social sytems of animals with discrete litters; non littermate siblings can only avoid mating if there is a generalizable mechanism for discriminating kin.
Social group or individual recognition, however, can function as kin recognition systems if family members that are collectively (group recognition) or individually recognized.
Kin recognition is known in a wide range of animals.
Greenberg L. 1979. Genetic component of bee odor In kin recognition.
Waldman, B. 1987. Mechanisms of kin recognition. J. Theor. Biol. 128:159-185.
Lacy R.C., Sherman P.W. 1983. Kin recognition by phenotype matching. Am. Nat. 121:489-512
Extreme cooperation: eusocial animals
In eusocial animals cooperation is taken to the next level; workers give up all or most of their individual reproductive potential in order to benefit the reproduction of their parents. Several explanations for the evolution of extreme cooperation in eusocial animals have been put forward. The most important are:examples of eusocial animals.
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