Changes: Reciprocal altruism

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In evolutionary biology, reciprocal altruism is a form of altruism in which one organism provides a benefit to another in the expectation of future reciprocation. This is equivalent to the Tit for tat strategy in game theory. It would only be expected to evolve in the presence of a mechanism to identify and punish "cheaters". An example of reciprocal altruism is blood-sharing in the vampire bat, in which bats feed regurgitated blood to those who have not collected much blood themselves knowing that they themselves may someday benefit from this same donation; cheaters are remembered by the colony and ousted from this collaboration.

In a series of ground-breaking contributions to biology in the early 1970s Robert Trivers introduced the theories of reciprocal altruism (1971), parental investment (1972), and parent-offspring conflict (1974). Trivers' paper "The Evolution of Reciprocal Altruism" (1971) elaborates the mathematics of reciprocal altruism and includes human reciprocal altruism as one of the three examples used to illustrate the model, arguing that "it can be shown that the details of the psychological system that regulates this altruism can be explained by this model." In particular, Trivers argues for the following characteristics as functional processes subserving reciprocal altruism:

A complex regulating system

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The system subserving reciprocal altruism will be sensitive and unstable because it will often pay to cheat. For reciprocal altruism to function, therefore, "natural selection will rapidly favour a complex psychological mechanism in each individual regulating both his own altruistic and cheating tendencies and his responses to these tendencies in others".

Friendship and the emotions of liking and disliking

The immediate emotional rewards motivating altruistic behaviour and partnerships will be the tendency to like others, to form friendships, and to act altruistically towards friends and likeable acquaintances. "Selection will favour liking those who are themselves altruistic" and for reproductive purposes.

Moralistic aggression

As cheaters will take advantage of any positive emotions motivating altruistic behaviour there will be selection for a protective mechanism. Moralistic aggression will "counteract the tendency of the altruist, in the absence of any reciprocity, to continue to perform altruistic acts for his own emotional rewards". It will also educate the unreciprocating individual, and in extreme cases "select directly against the unreciprocating individual by injuring… killing, or exiling him

Gratitude, sympathy, and the cost/benefit ratio of an altruistic act

Gratitude regulates the "human response to altruistic acts" and is sensitive to the cost/benefit ratio of such acts. In addition, sympathy "has been selected to motivate altruistic behaviour as a function of the plight of the recipient".

Guilt and reparative altruism

If cheating is detected then reciprocity will end, at considerable cost to the cheater, therefore "the cheater should be selected to make up for his misdeed and to show convincing evidence that he does not plan to continue his cheating sometime in the future". In order to motivate a reparative gesture "guilt has been selected for in humans partly in order to motivate the cheater to compensate his misdeed and to behave reciprocally in the future, and thus to prevent the rupture of reciprocal relationships".

Subtle cheating: the evolution of mimics

Selection will favour the mimicking of all traits subserving reciprocal altruism "in order to influence the behaviour of others to one's own advantage". Subtle cheating may involve sham moralistic aggression, sham guilt, sham sympathy, and "the hypocrisy of pretending one is in dire circumstances in order to induce sympathy-motivated altruistic behavior". Controversially, the resulting possibility of a stable evolutionary equilibrium with a low percentage of mimics is used to argue for the adaptivity of sociopathy.

Detection of the subtle cheater: trust-worthiness, trust, and suspicion

Selection will favour the detection of moralistic aggression and "distrusting those who perform altruistic acts without the emotional basis of generosity or guilt because the altruistic tendencies of such individuals may be less reliable in the future".

Setting up altruistic partnerships

Because "humans respond to acts of altruism with feelings of friendship that lead to reciprocity" selection will favour the strategy "do unto others as you would have them do unto you". Altruistic acts towards strangers and enemies may induce friendship.

Multiparty interactions

Particularly in ancestral times humans would have lived in small, close-knit groups where "selection may favour learning from the altruistic and cheating experiences of others, helping others coerce cheaters, forming multiparty exchange systems, and formulating rules for regulated exchanges in such multiparty systems".

Developmental plasticity

As the conditions under which reciprocal altruism can operate will vary widely according to ecological and social conditions, and will vary through time for the same population "one would expect selection to favour developmental plasticity of those traits regulating altruistic and cheating tendencies and responses to these tendencies in others". No simple developmental system would be expected to meet the requirements to be adaptive because "altruistic behaviour must be dispensed with regard to many characteristics of the recipient (including his degree of relationship, emotional makeup, past behaviour, friendships, and kin relations) of other members of the group, of the situation in which the altruistic behaviour takes place, and of many other parameters". Such a system could only function effectively through the developmental plasticity that would accommodate education about the appropriate response, especially from kin. For example, education of the sense of guilt could permit "those forms of cheating that local conditions make adaptive and to discourage those with more dangerous consequences".

See also: symbiosis.

References

Trivers, R.L. (1971). The evolution of reciprocal altruism. Quarterly Review of Biology. 46: 35-57.
Trivers, R.L. (1972). Parental investment and sexual selection. In B. Campbell (Ed.), Sexual selection and the descent of man, 1871-1971 (pp. 136-179). Chicago, IL: Aldine.
Trivers, R.L. (1974). Parent-offspring conflict. American Zoologist. 14: 249-264.
The Evolution of Cooperation, Robert Axelrod, Basic Books, ISBN 0465021212
The Selfish Gene, Richard Dawkins (1990), second edition -- includes two chapters about the evolution of cooperation, ISBN 0192860925

External links

Google scholar: reciprocal altruism

@@ Line 1: / Line 1: @@
-[[Robert Trivers]]' theory of '''parent-offspring conflict''' (1974) predicts that because the genetic interests of parents and offspring are not identical, offspring will be selected to manipulate their parents in order to ensure higher investment, and that, conversely, parents will be selected to manipulate their offspring.
+In [[evolutionary biology]], '''reciprocal altruism''' is a form of [[altruism]] in which one organism provides a benefit to another in the expectation of future [[reciprocation]]. This is equivalent to the [[Tit for tat]] strategy in [[game theory]]. It would only be expected to evolve in the presence of a mechanism to identify and punish "cheaters".
-An important illustration of such conflict is provided by David Haig’s work on genetic conflicts in pregnancy (1993). Haig has argued that [[fetus|fetal]] genes would be selected to draw more resources from the mother than it would be optimal for the mother to give, an hypothesis that has received empirical support. The [[placenta]], for example, secretes allocrine [[hormone]]s that decrease the sensitivity of the mother to [[insulin]] and thus make a larger supply of blood sugar available to the fetus. The mother responds by increasing the level of insulin in her bloodstream, and to counteract this effect the placenta has insulin receptors that stimulate the production of insulin-degrading [[enzyme]]s.
+An example of reciprocal altruism is blood-sharing in the [[vampire bat]], in which bats feed regurgitated blood to those who have not collected much blood themselves knowing that they themselves may someday benefit from this same donation; cheaters are remembered by the colony and ousted from this collaboration.
+In a series of ground-breaking contributions to biology in the early 1970s [[Robert Trivers]] introduced the theories of reciprocal altruism (1971), [[parental investment]] (1972), and [[parent-offspring conflict]] (1974). Trivers' paper "The Evolution of Reciprocal Altruism" (1971) elaborates the mathematics of reciprocal altruism and includes human reciprocal altruism as one of the three examples used to illustrate the model, arguing that "it can be shown that the details of the psychological system that regulates this altruism can be explained by this model." In particular, Trivers argues for the following characteristics as functional processes subserving reciprocal altruism:
-Only about 22 per-cent of human conceptions progress to full term and this creates a second arena for conflict between the mother and the fetus, because the fetus will have a lower quality cut off point for spontaneous abortion than the mother. The mother's quality cut-off point should also decline as she nears the end of her reproductive life and it may be significant that the offspring of older mothers have a higher incidence of genetic defects. Initially, the maintenance of pregnancy is controlled by the maternal hormone [[progesterone]], but in later stages it is controlled the fetal human chorionic gonadotrophin released into the maternal bloodstream, which causes the release of maternal progesterone. There is also conflict over blood supply to the placenta, with the fetus being prepared to demand a larger blood supply than is optimal for the mother. This results in [[hypertension]] and, significantly, high [[birth weight]] is positively correlated with maternal blood pressure.
-After birth the young infant may demand more resources than the mother is prepared to provide and the presence of [[benzodiazepine]]s in [[breast milk]] may be a counter to this strategy.
+== A complex regulating system ==
-Within the offspring there will be genetic conflict between the genes from the father and those from the mother, with paternally derived genes activating to facilitate a demand for greater resources. Evidence for this comes from [[Prader-Willi syndrome]] in which infants with two copies of the maternal chromosomal region 15q11-13 have a poor sucking response and weak cry. Conversely, infants with [[Angelman syndrome]] have two paternal copies of 15q11-13 and are active and display strong, but poorly coordinated, sucking. This latter effect is an instance of [[genomic imprinting]] in which the effects of genes differ depending on whether they are contributed by the father or the mother.
+{{cleanup-date|January 2006}}
+The system subserving reciprocal altruism will be sensitive and unstable because it will often pay to cheat. For reciprocal altruism to function, therefore, "natural selection will rapidly favour a complex psychological mechanism in each individual regulating both his own altruistic and cheating tendencies and his responses to these tendencies in others".
+=== Friendship and the emotions of liking and disliking ===
+The immediate emotional rewards motivating altruistic behaviour and partnerships will be the tendency to like others, to form friendships, and to act altruistically towards friends and likeable acquaintances. "Selection will favour liking those who are themselves altruistic" and for reproductive purposes.
+=== Moralistic aggression ===
+As cheaters will take advantage of any positive emotions motivating altruistic behaviour there will be selection for a protective mechanism. Moralistic aggression will "counteract the tendency of the altruist, in the absence of any reciprocity, to continue to perform altruistic acts for his own emotional rewards". It will also educate the unreciprocating individual, and in extreme cases "select directly against the unreciprocating individual by injuring… killing, or exiling him
+=== Gratitude, sympathy, and the cost/benefit ratio of an altruistic act ===
+Gratitude regulates the "human response to altruistic acts" and is sensitive to the cost/benefit ratio of such acts. In addition, sympathy "has been selected to motivate altruistic behaviour as a function of the plight of the recipient".
+=== Guilt and reparative altruism ===
+If cheating is detected then reciprocity will end, at considerable cost to the cheater, therefore "the cheater should be selected to make up for his misdeed and to show convincing evidence that he does not plan to continue his cheating sometime in the future". In order to motivate a reparative gesture "guilt has been selected for in humans partly in order to motivate the cheater to compensate his misdeed and to behave reciprocally in the future, and thus to prevent the rupture of reciprocal relationships".
+=== Subtle cheating: the evolution of mimics ===
+Selection will favour the mimicking of all traits subserving reciprocal altruism "in order to influence the behaviour of others to one's own advantage". Subtle cheating may involve sham moralistic aggression, sham guilt, sham sympathy, and "the hypocrisy of pretending one is in dire circumstances in order to induce sympathy-motivated altruistic behavior". Controversially, the resulting possibility of a stable evolutionary equilibrium with a low percentage of mimics is used to argue for the adaptivity of [[sociopathy]].
+=== Detection of the subtle cheater: trust-worthiness, trust, and suspicion ===
+Selection will favour the detection of moralistic aggression and "distrusting those who perform altruistic acts without the emotional basis of generosity or guilt because the altruistic tendencies of such individuals may be less reliable in the future".
+=== Setting up altruistic partnerships ===
+Because "humans respond to acts of altruism with feelings of friendship that lead to reciprocity" selection will favour the strategy "do unto others as you would have them do unto you". Altruistic acts towards strangers and enemies may induce friendship.
+=== Multiparty interactions ===
+Particularly in ancestral times humans would have lived in small, close-knit groups where "selection may favour learning from the altruistic and cheating experiences of others, helping others coerce cheaters, forming multiparty exchange systems, and formulating rules for regulated exchanges in such multiparty systems".
+=== Developmental plasticity ===
+As the conditions under which reciprocal altruism can operate will vary widely according to ecological and social conditions, and will vary through time for the same population "one would expect selection to favour [[phenotypic plasticity|developmental plasticity]] of those traits regulating altruistic and cheating tendencies and responses to these tendencies in others". No simple developmental system would be expected to meet the requirements to be adaptive because "altruistic behaviour must be dispensed with regard to many characteristics of the recipient (including his degree of relationship, emotional makeup, past behaviour, friendships, and kin relations) of other members of the group, of the situation in which the altruistic behaviour takes place, and of many other parameters". Such a system could only function effectively through the developmental plasticity that would accommodate education about the appropriate response, especially from kin. For example, education of the sense of guilt could permit "those forms of cheating that local conditions make adaptive and to discourage those with more dangerous consequences".
+''See also:'' [[symbiosis]].
 ==References==
-*Haig, D. (1993). Genetic conflicts in human pregnancy. ''Quarterly Review of Biology''. 68: 495-532.
+*[[Robert Trivers|Trivers, R.L.]] (1971). The evolution of reciprocal altruism. ''Quarterly Review of Biology''. 46: 35-57.
+*[[Robert Trivers|Trivers, R.L.]] (1972). Parental investment and sexual selection. In B. Campbell (Ed.), ''Sexual selection and the descent of man, 1871-1971'' (pp. 136-179). Chicago, IL: Aldine.
 *[[Robert Trivers|Trivers, R.L.]] (1974). Parent-offspring conflict. ''American Zoologist''. 14: 249-264.
+* ''[[The Evolution of Cooperation]]'', [[Robert Axelrod]], Basic Books,  ISBN 0465021212
+*''[[The Selfish Gene]]'', [[Richard Dawkins]] (1990), second edition -- includes two chapters about the evolution of cooperation, ISBN 0192860925
+==See also==
+*[[Norm of reciprocity]]
+*[[Altruism]]
+*[[Tit for tat]]
+*[[Iterated prisoner's dilemma]]
 ==External links==
-*[http://scholar.google.com/scholar?sourceid=mozclient&num=50&scoring=d&ie=utf-8&oe=utf-8&q=Genetic+conflicts+in+human+pregnancy Genetic conflicts in human pregnancy]
+*[http://scholar.google.com/scholar?sourceid=mozclient&num=50&scoring=d&ie=utf-8&oe=utf-8&q=%22reciprocal+altruism%22 Google scholar: reciprocal altruism]
-*[http://scholar.google.com/scholar?num=50&hl=en&lr=&safe=off&scoring=d&q=Parent-offspring+conflict&btnG=Search Parent-offspring conflict]
 [[Category:Evolution]]