Altruism in animals
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Altruism in animals describes a range of behaviours performed by animals that may be to their own disadvantage but which benefit others. Other definitions place emphasis on the genetic consequences of altruism, e.g. altruism is "Instinctive behavior that is detrimental to the individual but favors the survival or spread of that individual's genes, as by benefiting its relatives." or the biological fitness of the animals, e.g. "Altruism refers to behavior by an individual that increases the fitness of another individual while decreasing the fitness of the actor. Altruism appears most obviously in kin relationships but may also be evident amongst wider social groups.
Altruism in animals is not identical to the everyday concept of altruism in humans. In humans, an action would only be called "altruistic" if it was done with the conscious intention of helping another. But in the animal behaviour sense there is no such requirement. Indeed, some of the most interesting examples of altruism in animals are found among species that are presumably not capable of conscious thought, e.g. insects. For the animal biologist, it is the consequences of an action for reproductive fitness that determine whether the action counts as altruistic, not the intentions, if any, with which the action is performed.
In the science of 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. The theory of natural selection proposed by Charles Darwin leads us to expect animals to behave in ways that increase their own chances of survival and reproduction, not those of others. But by behaving altruistically, an animal reduces its own fitness, so should be at a selective disadvantage. Researchers on alleged altruistic behaviours among animals have been ideologically opposed to the social Darwinist concept of the "survival of the fittest", under the name of "survival of the nicest" — the latter being globally compatible, however, with the theory of evolution by natural selection. Insistence on such cooperative behaviours between animals was first exposed by the Russian zoologist and anarchist Peter Kropotkin in his 1902 book, Mutual Aid: A Factor of Evolution.
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 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. In the 1960s and 1970s the rival theory of kin selection emerged, due originally to W. D. Hamilton. Kin selection is an instance of inclusive fitness, which combines the number of offspring produced with the number an individual can produce by supporting others, such as siblings. This theory showed how altruistic behaviour could evolve without the need for group-level selection, and quickly gained prominence among biologists interested in the evolution of social behaviour.
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Recent developments in game theory have provided some explanations for apparent altruism, as have traditional evolutionary analyses. Among the proposed mechanisms are:
- Behavioural manipulation (for example, by certain parasites that can alter the behavior of the host)
- Bounded rationality (for example, Herbert A. Simon)
- Kin selection including eusociality (see also "The Selfish Gene")
- Memes (by influencing behavior to favor their own spread; see religion as a meme)
- Reciprocal altruism, mutual aid
- Sexual selection, in particular, the Handicap principle
Social behavior and altruism share many similarities to the interactions between the many parts (cells, genes) of an organism, but are distinguished by the ability of each individual to reproduce indefinitely without an absolute requirement for its neighbors.
Altruist theories in evolutionary biology were contested by Amotz Zahavi, the inventor of the signalling theory and its correlative, the handicap principle, based mainly on his observations of the Arabian Babbler, a bird commonly known for its surprising (alleged) altruistic behaviours.
Researchers in Switzerland have developed an algorithm based on Hamilton's rule of kin selection. The algorithm shows how altruism in a swarm of entities can, over time, evolve and result in more effective swarm behaviour.
Examples in vertebrates
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- Dogs often adopt orphaned cats, squirrels, ducks, and even tigers.
- Wolves and wild dogs bring meat back to members of the pack not present at the kill.
- Mongooses support elderly, sick, or injured animals
- Meerkats often have one standing guard to warn whilst 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 handicapped 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 animals, 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.
- 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 
Examples in invertebrates
- Some termites and ants release a sticky secretion by fatally rupturing a specialized gland. This autothysis altruistically aids the colony at the expense of the individual insect. For example, defending against invading ants by creating a tar baby effect. 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 specific genetic make-up).
Examples in protists
An interesting 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.
- Cheating (biology)
- Evolutionarily stable strategy
- Gene-centered view of evolution
- Evolution of morality
- Evolutionary ethics
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- Quick Guide: Altruism (Current Biology)
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