Reciprocal altruism

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Reciprocal altruism is a theory that aims to explain the evolution of altruistic behavior between unrelated individuals through natural selection . It was published by Robert Trivers in 1971 .

Description and requirements

Altruism is usually defined as the behavior of one individual in favor of another individual, with the behavior bringing the altruistic individual directly more costs than benefits. Such a definition does not conflict with the fact that altruistic behavior has a long-term positive effect on the reproductive success ( fitness ) of the altruistic individual or individuals related to him. However, a prerequisite for the biological-evolutionary formation of any altruistic behavior is that the overall benefit of the altruistic behavior is positive.

Characteristics of specifically reciprocal altruism between unrelated individuals are:

  • Altruistic behavior is balanced between the interacting individuals.
  • In the reciprocal relationships, individuals alternate between the roles of giver and receiver.
  • The total benefit of reciprocal altruistic behavior exceeds its total cost.

An animal can, at its own expense, provide another animal with no fitness disadvantage if the beneficiary reciprocates this advantage at a later point in time. The prerequisite is a level of intelligence that can identify fraudulent behavior. This requirement is important because, from an evolutionary perspective, altruistic behavior is always prone to being exploited by non-reciprocating individuals. Punishments are also necessary. The memory must also be strong enough to recognize fraudsters . Because of these premises, reciprocal altruism works best in intelligent, social, and long-lived species. According to psychologist Robin Dunbar , human language evolved as it made it easier to identify scammers.

Non-human primates

Most primates live in stable social groups. It is not known whether primates have the cognitive abilities to remember specific behaviors of other individuals towards them. Primates are at least very intelligent and capable of solving complex problems. Reciprocal grooming and alliances have been observed in several species of macaques , baboons , vervet monkeys, and chimpanzees . In some cases grooming and support were exchanged for benefits in kind, in others grooming for support. Some monkeys take turns grooming so that time is balanced between individuals during each grooming phase. Other monkeys balance this time over several grooming phases.

In male chimpanzees, social bonds seem to be based on reciprocal exchanges of many different services. Chimpanzees in Kibale National Park selectively share meat with individuals who have shared meat with them or who provide regular support. Males who hunt together tend to be more selective in grooming and assisting one another, as well as patrolling borders together. These males are not related. These correlations are consistent with the theory of reciprocal altruism, but do not prove that these altruistic behaviors are due to reciprocity. However, several studies have suggested it.

In an experiment, green monkeys were played on tapes for help from other monkeys. The audition takes place in two different situations. In the first situation, monkey A had groomed monkey B's coat before. Monkey B reacted comparatively quickly to the played call for help from monkey A. In the second situation, no grooming had taken place beforehand. Here, too, monkey B reacted to the played call for help from monkey A - but more slowly.

In another experiment by Frans de Waal , various individuals in a group of chimpanzees were given multiple bundles of leaves over a period of three years. The individuals could keep these bundles to themselves; however, the bundles were often divided. The owners of the bundles were always more generous towards those individuals who had groomed the owner's fur a short time beforehand. The owners of the leaves were also less resistant to attempts by individuals to appropriate parts of the bundle if these individuals had previously tended to the owner's coat.

The number of well-documented cases of reciprocal altruism in non-human primates is still small overall. It is therefore possible that such behavior is rare in nature. However, reciprocal altruism may be more common than observed. Altruism has the potential to manifest itself in a variety of ways (e.g., grooming, protecting against predators), and it is very difficult to quantify the costs and benefits of all of these altruistic behaviors.

Development of the concept

Triver's concept of mutual altruism, which Axelrod and Hamilton successfully implemented as a tit for tat strategy for two-person interactions in game theory , has not proven itself when describing groups in common property games .


  • Robert Trivers: The evolution of reciprocal altruism. In: Quarterly Review of Biology . Volume 46, 1971, pp. 35-57. (Full text: PDF , 2.52 MB)

Individual evidence

  1. ^ A b Stanley A. Rice: Encyclopedia of evolution. Checkmark Books, 2007, ISBN 978-0-8160-7121-0 , p. 16 f.
  2. a b c d e f Robert Boyd , Joan B. Silk: How Humans Evolved. Fourth Edition. Norton, 2006, ISBN 0-393-92628-1 , pp. 213 ff.
  3. Ernst Fehr: Human behavior: Don't lose your reputation . In: Nature . No. 432 , November 25, 2004, p. 449-450 , doi : 10.1038 / 432449a . read online , (PDF 345 kB, accessed September 15, 2015)