Reciprocal altruism


Diagram showing reciprocal altruism

In 1987 Trivers told a symposium on reciprocity that he had originally submitted his article under the title "The Evolution of Delayed Return Altruism", but reviewer W. D. Hamilton suggested that he change the title to "The Evolution of Reciprocal Altruism". Trivers changed the title, but not the examples in the manuscript, which has led to confusion about what were appropriate examples of reciprocal altruism for the last 50 years. In their contribution to that symposium, Rothstein and Pierotti (1988)[1] addressed this issue and proposed new definitions concerning the topic of altruism, that clarified the issue created by Trivers and Hamilton. They proposed that Delayed Return Altruism was a superior concept and used the term pseudo-reciprocity in place of DRA. For some reason, the paper by Rothstein and Pierotti did not catch hold, but it remains one of the best examinations of the relationship between altruism and kin selection. Rothstein and Pierotti also explain why Trivers' examples of Reciprocal Altruism are actually examples of delayed return altruism.



Putting this into the form of a strategy in a repeated prisoner's dilemma would mean to cooperate unconditionally in the first period and behave cooperatively (altruistically) as long as the other agent does as well.[2] If chances of meeting another reciprocal altruist are high enough, or if the game is repeated for a long enough amount of time, this form of altruism can evolve within a population.

This is close to the notion of "tit for tat" introduced by Anatol Rapoport,[4] although there still seems a slight distinction in that "tit for tat" cooperates in the first period and from thereon always replicates an opponent's previous action, whereas "reciprocal altruists" stop cooperation in the first instance of non-cooperation by an opponent and stay non-cooperative from thereon. This distinction leads to the fact that in contrast to reciprocal altruism, tit for tat may be able to restore cooperation under certain conditions despite cooperation having broken down.

Christopher Stephens shows a set of necessary and jointly sufficient conditions "... for an instance of reciprocal altruism:[5]

  1. the behaviour must reduce a donor's fitness relative to a selfish alternative;[5]
  2. the fitness of the recipient must be elevated relative to non-recipients;[5]
  3. the performance of the behaviour must not depend on the receipt of an immediate benefit;[5]
  4. conditions 1, 2, and 3 must apply to both individuals engaging in reciprocal helping.[5]

There are two additional conditions necessary "...for reciprocal altruism to evolve:"[5]

  • A mechanism for detecting 'cheaters' must exist.[5]
  • A large (indefinite) number of opportunities to exchange aid must exist.[5]

The first two conditions are necessary for altruism as such, while the third is distinguishing reciprocal altruism from simple mutualism and the fourth makes the interaction reciprocal. Condition number five is required as otherwise non-altruists may always exploit altruistic behaviour without any consequences and therefore evolution of reciprocal altruism would not be possible. However, it is pointed out that this "conditioning device" does not need to be conscious. Condition number six is required to avoid cooperation breakdown through backwards induction—a possibility suggested by game theoretical models.[5]



Cleaner fishEdit


An example of reciprocal altruism is cleaning symbiosis, such as between cleaner fish and their hosts, though cleaners include shrimps and birds, and clients include fish, turtles, octopuses and mammals.[6] Aside from the apparent symbiosis of the cleaner and the host during actual cleaning, which cannot be interpreted as altruism, the host displays additional behaviour that meets the criteria for delayed return altruism:

The host fish allows the cleaner fish free entrance and exit and does not eat the cleaner, even after the cleaning is done.[7][8][9][10] The host signals the cleaner it is about to depart the cleaner's locality, even when the cleaner is not in its body. The host sometimes chases off possible dangers to the cleaner.[10]

The following evidence supports the hypothesis:

The cleaning by cleaners is essential for the host. In the absence of cleaners the hosts leave the locality or suffer from injuries inflicted by ectoparasites.[11] There is difficulty and danger in finding a cleaner. Hosts leave their element to get cleaned.[10] Others wait no longer than 30 seconds before searching for cleaners elsewhere.[7]


This example meets some, but not all, of the criteria described in Trivers's model. In the cleaner-host system the benefit to the cleaner is always immediate. However, the evolution of reciprocal altruism is contingent on opportunities for future rewards through repeated interactions. In one study, nearby host fish observed "cheater" cleaners and subsequently avoided them.[13] In these examples, true reciprocity is difficult to demonstrate since failure means the death of the cleaner. However, if Randall's claim that hosts sometimes chase off possible dangers to the cleaner is correct, an experiment might be constructed in which reciprocity could be demonstrated.[9] In actuality this is one of Trivers' examples of Delayed Return Altruism as discussed by Rothstein and Pierotti 1988.

Warning calls in birdsEdit



It has been shown that predators learn specific localities and specialize individually on prey types and hunting techniques.[14][15][16][17] It is therefore disadvantageous for a bird to have a predator eat a conspecific, because the experienced predator may then be more likely to eat him. Alarming another bird by giving a warning call tends to prevent predators from specializing on the caller's species and locality. In this way, birds in areas in which warning calls are given will be at a selective advantage relative to birds in areas free from warning calls.




Nest protectingEdit



Vampire batsEdit

Vampire bats also display reciprocal altruism, as described by Wilkinson.[19][20] The bats feed each other by regurgitating blood. Since bats only feed on blood and will die after just 70 hours of not eating, this food sharing is a great benefit to the receiver and a great cost to the giver.[21] To qualify for reciprocal altruism, the benefit to the receiver would have to be larger than the cost to the donor. This seems to hold as these bats usually die if they do not find a blood meal two nights in a row. Also, the requirement that individuals who have behaved altruistically in the past are helped by others in the future is confirmed by the data.[19] However, the consistency of the reciprocal behaviour, namely that a previously non-altruistic bat is refused help when it requires it, has not been demonstrated. Therefore, the bats do not seem to qualify yet as an unequivocal example of reciprocal altruism.


Grooming in primates meets the conditions for reciprocal altruism according to some studies. One of the studies in vervet monkeys shows that among unrelated individuals, grooming induce higher chance of attending to each other's calls for aid.[22] However, vervet monkeys also display grooming behaviors within group members, displaying alliances.[23] This would demonstrate vervet monkey's grooming behavior as a part of kin selection since the activity is done between siblings in this study. Moreover, following the criteria by Stephen,[5] if the study is to be an example of reciprocal altruism, it must prove the mechanism for detecting cheaters.


Numerous species of bacteria engage in reciprocal altruistic behaviors with other species. Typically, this takes the form of bacteria providing essential nutrients for another species, while the other species provides an environment for the bacteria to live in. Reciprocal altruism is exhibited between nitrogen-fixing bacteria and plants in which they reside. Additionally, it can be observed between bacteria and some species of flies such as Bactrocera tyroni. These flies consume nutrient-producing bacteria found on the leaves of plants; in exchange, they reside within the flies' digestive system.[24] This reciprocal altruistic behavior has been exploited by techniques designed to eliminate B. tyroni, which are fruit fly pests native to Australia.[25]

Regulation by emotional dispositionEdit

In comparison to that of other animals, the human altruistic system is a sensitive and unstable one.[2] Therefore, the tendency to give, to cheat, and the response to other's acts of giving and cheating must be regulated by a complex psychology in each individual, social structures, and cultural traditions. Individuals differ in the degree of these tendencies and responses. According to Trivers, the following emotional dispositions and their evolution can be understood in terms of regulation of altruism.[2]

  • Friendship and emotions of liking and disliking.
  • Partnerships. Altruism to create friendships.

It is not known how individuals pick partners as there has been little research on choice. Modeling indicates that altruism about partner choices is unlikely to evolve, as costs and benefits between multiple individuals are variable.[26] Therefore, the time or frequency of reciprocal actions contributes more to an individual's choice of partner than the reciprocal act itself.

See alsoEdit


  1. ^ Rothstein, S. I. (1988). "Distinctions among reciprocal altruism and kin selection, and a model for the initial evolution of helping behavior". Ethology and Sociobiology. 9: 189–210. doi:10.1016/0162-3095(88)90021-0.
  4. ^ a b Dawkins, Richard (2006). The Selfish Gene (30th Anniversary ed.). Oxford University Press. ISBN 0-19-929114-4.
  6. ^ Grutter, Alexandra S. (2002). "Cleaning symbioses from the parasites' perspective". Parasitology. 124 (7): S65–S81. doi:10.1017/S0031182002001488. PMID 12396217. S2CID 26816332.
  8. ^ Heidiger, H. (1968). "Putzer-fische im aquarium". Natur und Museum. 98: 89–96.
  9. ^ a b c Randall, J. E. (1958). "A review of the Labrid fish genus Labriodes with descriptions of two new species and notes on ecology" (PDF). Pacific Science. 12 (4): 327–347.
  11. ^ a b Feder, H.M. (1966). "Cleaning symbioses in the marine environment". In Henry, S.M. (ed.). Symbiosis. 1. Academic Press. pp. 327–380. OCLC 841865823.
  13. ^ Bshary, R. (2002). "Biting cleaner fish use altruism to deceive image-scoring client reef fish". Proceedings of the Royal Society B. 269 (1505): 2087–93. doi:10.1098/rspb.2002.2084. PMC 1691138. PMID 12396482.
  14. ^ Murie, Adolph (1944). Fauna of the National Parks of the United States: Fauna series. Fauna of National Parks of the United States. Faunal Series No. 5. U.S. Government Printing Office.
  16. ^ Tinbergen, N. (1968). "On war and peace in animals and man". Science. 160 (3835): 1411–8. Bibcode:1968Sci...160.1411T. doi:10.1126/science.160.3835.1411. PMID 5690147.
  17. ^ Owen, D. F. (1963). "Similar polymorphismas in an insect and a land snail". Nature. 198 (4876): 201–3. Bibcode:1963Natur.198..201O. doi:10.1038/198201b0. S2CID 4262191.
  18. ^ Olendorf, Robert; Getty, Thomas; Scribner, Kim (22 January 2004). "Cooperative Nest Defence in Red–winged Blackbirds: Reciprocal Altruism, Kinship or By–product Mutualism?". Proc. R. Soc. Lond. B. 271 (1535): 177–182. doi:10.1098/rspb.2003.2586. JSTOR 4142499. PMC 1691571. PMID 15058395.
  19. ^ a b Wilkinson, G. (1984). "Reciprocal Food Sharing in the Vampire Bat". Nature. 308 (5955): 181–184. Bibcode:1984Natur.308..181W. doi:10.1038/308181a0. PMC 3574350. PMID 23282995.
  21. ^ Carter, Gerald (January 2, 2013). "Food Sharing in Vampire Bats: Reciprocal Help Predicts Donations More than Relatedness or Harassment". Proceedings of the Royal Society. 280 (1753): 20122573. doi:10.1098/rspb.2012.2573. PMC 3574350. PMID 23282995.
  22. ^ Seyfarth, Robert M; Cheney, Dorothy L (1984). "Grooming, alliances and reciprocal altruism in vervet monkeys". Nature. 308 (5959): 541–3. Bibcode:1984Natur.308..541S. doi:10.1038/308541a0. PMID 6709060. S2CID 4266889.
  24. ^ Clarke, A.R.; Powell, K.S.; Weldon, C.W.; Taylor, P.W. (2010-11-02). "The ecology of Bactrocera tryoni (Diptera: Tephritidae): what do we know to assist pest management?" (PDF). Annals of Applied Biology. 158 (1): 26–54. doi:10.1111/j.1744-7348.2010.00448.x. ISSN 0003-4746.
  25. ^ Bateman, MA (1967). "Adaptations to temperature in geographic races of the Queensland fruit fly Dacus (Strumenta) tryoni". Australian Journal of Zoology. 15 (6): 1141. doi:10.1071/zo9671141. ISSN 0004-959X.
  26. ^ Schino, G.; Aureli, F. (2010). "A few misunderstandings about reciprocal altruism". Commun. Integr. Biol. 3 (6): 561–3. doi:10.4161/cib.3.6.12977. PMC 3038063. PMID 21331239.