Editing Reciprocal altruism (section)

==Examples==
The following examples could be understood as altruism. However, showing reciprocal altruism in an unambiguous way requires more evidence as will be shown later.

===Cleaner fish===
{{further|Cleaning symbiosis}}
[[File:Cleaner station komodo.jpg|thumb|250px|[[Cleaning symbiosis]]: a small cleaner [[wrasse]] (''Labroides dimidiatus'') with [[Animal coloration|advertising coloration]] services a big eye squirrelfish (''[[Priacanthidae|Priacanthus hamrur]]'') in an apparent example of reciprocal altruism.]]

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.<ref name=Grutter>{{cite journal | title=Cleaning symbioses from the parasites' perspective | author=Grutter, Alexandra S. | journal=Parasitology | year=2002 | volume=124 | issue=7 | pages=S65–S81 | doi=10.1017/S0031182002001488| pmid=12396217 | s2cid=26816332 }}</ref>   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.<ref name="Eibel-Eibesfeldt">{{cite journal | doi = 10.1111/j.1439-0310.1955.tb01523.x | title = Über Symbiosen, Parasitismus und andere besondere zwischenartliche Beziehungen tropischer Meeresfische1 | year = 2010 | last1 = Eibi-Eibesfeldt | first1 = T | journal = Zeitschrift für Tierpsychologie | volume = 12 | issue = 2 | pages = 203–219 }}</ref><ref name="Heidiger">{{cite journal |first=H. |last=Heidiger |title=Putzer-fische im aquarium |journal=Natur und Museum |volume=98 |pages=89–96 |year=1968 }}</ref><ref name="Randall1">{{cite journal | last1 = Randall | first1 = J. E. | year = 1958 | title = A review of the Labrid fish genus Labriodes with descriptions of two new species and notes on ecology | journal = Pacific Science | volume = 12 | issue =4 | pages = 327–347 |url=https://scholarspace.manoa.hawaii.edu/bitstream/10125/7923/vol12n4-327-347.pdf |archive-url=https://web.archive.org/web/20200806161617/https://scholarspace.manoa.hawaii.edu/bitstream/10125/7923/vol12n4-327-347.pdf |archive-date=2020-08-06 |url-status=live}}</ref><ref name="Randall2">{{cite journal | last1 = Randall | first1 = J. E. | year = 1962 | title = Fish service stations | journal = Sea Frontiers | volume = 8 | pages = 40–47 }}</ref> 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.<ref name="Randall2" />

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]].<ref name="Feder">{{cite book |first=H.M. |last=Feder |chapter=Cleaning symbioses in the marine environment |editor-first=S.M. |editor-last=Henry |title=Symbiosis |publisher=Academic Press |year=1966 |pages=327–380 |oclc=841865823 |volume=1}}</ref> There is difficulty and danger in finding a cleaner. Hosts leave their element to get cleaned.<ref name="Randall2" /> Others wait no longer than 30 seconds before searching for cleaners elsewhere.<ref name="Eibel-Eibesfeldt" />

A key requirement for the establishment of reciprocal altruism is that the same two individuals must interact repeatedly, as otherwise the best strategy for the host would be to eat the cleaner as soon as cleaning was complete. This constraint imposes both a spatial and a temporal condition on the cleaner and on its host. Both individuals must remain in the same physical location, and both must have a long enough lifespan, to enable multiple interactions. There is reliable evidence that individual cleaners and hosts do indeed interact repeatedly.<ref name="Randall1" /><ref name="Feder" /><ref name="Limbaugh">{{cite journal | last1 = Limbaugh | first1 = C. | last2 = Pederson | first2 = H. | last3 = Chase | first3 = F. | year = 1961 | title = Shrimps that clean fishes | url =http://www.ingentaconnect.com/content/umrsmas/bullmar/1961/00000011/00000001/art00011 | journal = Bull. Mar. Sci. Gulf Caribb. | volume = 11 | issue =1 | pages = 237–257 }}</ref>

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.<ref name="bshary">{{cite journal | last1 = Bshary | first1 = R. | year = 2002 | title = Biting cleaner fish use altruism to deceive image-scoring client reef fish | journal = Proceedings of the Royal Society B | volume = 269 | issue = 1505 | pages = 2087–93 | doi=10.1098/rspb.2002.2084| pmid = 12396482 | pmc = 1691138 }}</ref> 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.<ref name="Randall1" />  In actuality this is one of Trivers' examples of Delayed Return Altruism as discussed by Rothstein and Pierotti 1988.

===Warning calls in birds===
[[File:2012-06-09 16-04-22 Switzerland Kanton Graubünden Sagliaz cropped.JPG|thumb|Eurasian jay, ''[[Garrulus glandarius]]'', gives loud alarm calls from its tree perch when it sees a predator.]]
{{further|Signalling theory}}

Warning calls, although exposing a bird and putting it in danger, are frequently given by birds. An explanation in terms of altruistic behaviors given by Trivers:<ref name="trivers"/>

It has been shown that predators learn specific localities and specialize individually on prey types and hunting techniques.<ref name="Murie">{{cite book |first=Adolph |last=Murie |title=Fauna of the National Parks of the United States: Fauna series |url=https://books.google.com/books?id=HO_aAAAAMAAJ |year=1944 |publisher=U.S. Government Printing Office |series=Fauna of National Parks of the United States |volume=Faunal Series No. 5}}</ref><ref name="Southern">{{cite journal | last1 = Southern | first1 = H. N. | year = 1954 | title = Tawny owls and their prey | journal = Ibis | volume = 96 | issue = 3| pages = 384–410 |doi=10.1111/j.1474-919X.1954.tb02332.x}}</ref><ref name="Tinbergen">{{cite journal | last1 = Tinbergen | first1 = N. | year = 1968 | title = On war and peace in animals and man | journal = Science | volume = 160 | issue = 3835| pages = 1411–8 | doi = 10.1126/science.160.3835.1411 | pmid = 5690147 |bibcode = 1968Sci...160.1411T }}</ref><ref name="Owen">{{cite journal | last1 = Owen | first1 = D. F. | year = 1963 | title = Similar polymorphismas in an insect and a land snail | journal = Nature | volume = 198 | issue = 4876| pages = 201–3 | doi = 10.1038/198201b0 |bibcode = 1963Natur.198..201O | s2cid = 4262191 }}</ref>
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 them. 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.

Nevertheless, this presentation lacks important elements of reciprocity. It is very hard to detect and ostracize cheaters. There is no evidence that a bird refrains from giving calls when another bird is not reciprocating, nor evidence that individuals interact repeatedly. Given the aforementioned characteristics of bird calling, a continuous bird emigration and immigration environment (true of many avian species) is most likely to be partial to cheaters, since selection against the [[Gene-centered view of evolution|selfish gene]]<ref name=Dawkins06 /> is unlikely.<ref name="trivers" />

Another explanation for warning calls is that these are not warning calls at all:
A bird, once it has detected a bird of prey, calls to signal to the bird of prey that it was detected, and that there is no use trying to attack the calling bird. Two facts support this hypothesis:

* The call frequencies match the hearing range of the predator bird.
* Calling birds are less attacked—predator birds attack calling birds less frequently than other birds.

===Nest protecting===

[[File:Arctic tern (Sterna paradisaea) attacking, Amsterdam island, Svalbard.jpg|thumb|[[Arctic tern]]s protect their offspring extremely aggressively by very quick drop-downs from a stationary flight over their enemies. Other birds often benefit from this behavior by breeding very close to the Arctic terns.]]
[[Red-winged blackbird]] males help defend neighbor's nests. There are many theories as to why males behave this way. One is that males only defend other nests which contain their extra-pair offspring. Extra-pair offspring are juveniles which may contain some of the male bird's DNA. Another is the tit-for-tat strategy of reciprocal altruism. A third theory is, males help only other closely related males. A study done by The Department of Fisheries and Wildlife provided evidence that males used a tit-for-tat strategy. The Department of Fisheries and Wildlife tested many different nests by placing stuffed crows by nests, and then observing behavior of neighboring males. The behaviors they looked for included the number of calls, dives, and strikes. After analyzing the results, there was not significance evidence for kin selection; the presence of extra-pair offspring did not affect the probability of help in nest defense. However, males reduced the amount of defense given to neighbors when neighbor males reduced defense for their nests. This demonstrates a tit-for-tat strategy, where animals help those who previously helped them. This strategy is one type of reciprocal altruism.<ref>{{cite journal |last1=Olendorf |first1=Robert |first2=Thomas |last2=Getty |first3=Kim |last3=Scribner |title=Cooperative Nest Defence in Red–winged Blackbirds: Reciprocal Altruism, Kinship or By–product Mutualism? |journal=Proc. R. Soc. Lond. B |volume=271 |issue=1535 |pages=177–182 |date=22 January 2004 |doi=10.1098/rspb.2003.2586 |jstor=4142499 |pmid=15058395 |pmc=1691571}}</ref>

===Vampire bats===
[[Vampire bats]] also display reciprocal altruism, as described by Wilkinson.<ref name="Wilkinson1">{{cite journal | last1 = Wilkinson | first1 = G. | year = 1984 | title = Reciprocal Food Sharing in the Vampire Bat | journal = Nature | volume = 308 | issue = 5955| pages = 181–184 | doi=10.1038/308181a0 | pmid = 23282995 | pmc = 3574350 | bibcode=1984Natur.308..181W }}</ref><ref name="Wilkinson2">{{cite journal | last1 = Wilkinson | first1 = G. | year = 1988 | title = Reciprocal Altruism in Bats and Other Mammals | journal = Ethology and Sociobiology | volume = 9 | issue =2–4 | pages = 85–100 | doi=10.1016/0162-3095(88)90015-5 }}</ref>
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.<ref>{{cite journal|last1=Carter|first1=Gerald|title=Food Sharing in Vampire Bats: Reciprocal Help Predicts Donations More than Relatedness or Harassment | journal=Proceedings of the Royal Society|volume=280|issue=1753|pages=20122573|date=January 2, 2013 |pmc=3574350|pmid=23282995|doi=10.1098/rspb.2012.2573}}</ref>
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.<ref name="Wilkinson1" /> 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.

===Primates===
Grooming in primates meets the conditions for reciprocal altruism according to some studies.  One of the studies in [[vervet monkey]]s shows that among unrelated individuals, grooming induce higher chance of attending to each other's calls for aid.<ref>{{Cite journal |title = Grooming, alliances and reciprocal altruism in vervet monkeys|last1 = Seyfarth|first1 = Robert M|date = 1984|journal = Nature |volume=308 |issue = 5959|pages=541–3|doi = 10.1038/308541a0|pmid = 6709060 |first2 = Dorothy L|last2 = Cheney|bibcode = 1984Natur.308..541S|s2cid = 4266889}}</ref> However, vervet monkeys also display grooming behaviors within group members, displaying alliances.<ref name="sibships">{{cite journal | last1 = Lee | first1 = P.C. | year = 1987 | title = Sibships: Cooperation and Competition Among Immature Vervet Monkeys. | journal = [[Primates (journal)|Primates]] | volume = 28 | issue = 1| pages = 47–59 | doi=10.1007/bf02382182| s2cid = 21449948 }}</ref> 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,<ref name="Stephens" /> if the study is to be an example of reciprocal altruism, it must prove the mechanism for detecting cheaters.

=== Bacteria ===
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 tryoni]]''. These flies consume nutrient-producing bacteria found on the leaves of plants; in exchange, they reside within the flies' digestive system.<ref>{{Cite journal|last1=Clarke|first1=A.R.|last2=Powell|first2=K.S.|last3=Weldon|first3=C.W.|last4=Taylor|first4=P.W.|date=2010-11-02|title=The ecology of ''Bactrocera tryoni'' (Diptera: Tephritidae): what do we know to assist pest management?|journal=Annals of Applied Biology|volume=158|issue=1|pages=26–54|doi=10.1111/j.1744-7348.2010.00448.x|issn=0003-4746|url=https://eprints.qut.edu.au/40107/1/c40107.pdf |archive-url=https://web.archive.org/web/20181104094758/http://eprints.qut.edu.au/40107/1/c40107.pdf |archive-date=2018-11-04 |url-status=live|hdl=10019.1/122744|hdl-access=free}}</ref> This reciprocal altruistic behavior has been exploited by techniques designed to eliminate ''B. tryoni'', which are fruit fly pests native to Australia.<ref>{{Cite journal|last=Bateman|first=MA|date=1967|title=Adaptations to temperature in geographic races of the Queensland fruit fly ''Dacus (Strumenta) tryoni'' |journal=Australian Journal of Zoology|volume=15|issue=6|pages=1141|doi=10.1071/zo9671141|issn=0004-959X}}</ref>

=== Humans ===
{{Main|Reciprocal altruism in humans}}Examples of reciprocal altruism in humans include helping injured individuals, sharing food, tools, or knowledge,<ref>{{Cite journal |last=Trivers |first=Robert L. |date=March 1971 |title=The Evolution of Reciprocal Altruism |url=https://doi.org/10.1086/406755 |journal=The Quarterly Review of Biology |volume=46 |issue=1 |pages=35–57 |doi=10.1086/406755 |issn=0033-5770}}</ref> and providing assistance in crises with the expectation of future aid. In social interactions, individuals often engage in direct reciprocity, such as returning favors or lending resources with an implicit understanding of future repayment. Indirect reciprocity is also observed,<ref>{{Cite journal |last=Nowak |first=Martin A. |last2=Sigmund |first2=Karl |date=October 2005 |title=Evolution of indirect reciprocity |url=https://doi.org/10.1038/nature04131 |journal=Nature |volume=437 |issue=7063 |pages=1291–1298 |doi=10.1038/nature04131 |issn=0028-0836}}</ref> where individuals help others based on reputation, encouraging mutual cooperation within a community. Economic and political systems rely on reciprocal altruism through trade agreements, diplomatic alliances,<ref>{{Cite journal |last=Keohane |first=Robert O. |date=1986 |title=Reciprocity in international relations |url=https://doi.org/10.1017/s0020818300004458 |journal=International Organization |volume=40 |issue=1 |pages=1–27 |doi=10.1017/s0020818300004458 |issn=0020-8183}}</ref> and social contracts, where long-term benefits outweigh short-term costs. Additionally, studies in [[game theory]], such as the [[Prisoner's dilemma|Prisoner’s Dilemma]], illustrate how cooperative behaviors emerge and stabilize when individuals recognize the advantages of mutual support.