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Altruism is a well-documented animal behaviour, which appears most obviously in kin relationships but may also be evident amongst wider social groups.
Altruism : Kinship and reciprocity
Research in evolutionary theory has been applied to social behaviour, including altruism. Some animal altruistic behaviour is explained by kin selection. Beyond the physical exertions that mothers, and in some species fathers, undertake to protect their young, extreme examples of sacrifice may occur. One example is matriphagy (the comsumption of the mother by her offspring) in the spider Stegodyphus. 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.
Examples of animal altruism
- Dolphins support sick or injured animals, swimming under them for hours at a time and pushing them to the surface so they can breathe,
- 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.
- Vampire bats regularly regurgitate blood and donate it to other members of their group who have failed to feed that night, ensuring they do not starve,
- In numerous bird species, a breeding pair receives help in raising its young from other "helper" birds, who protect the nest from predators and help to feed the fledglings,
- Most mammal carnivores like wolves or dogs have a habit of not harming pack members below certain age, of opposite sex or in surrendering position (in case of some animals, the behavior exists within entire species rather than one pack),
- 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.
- Animal rights
- Evolutionary game theory
- The Descent of Man
- Natural selection
- Evolutionarily stable strategy
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