Reciprocal altruism

thumb|upright=1.75|Diagram showing reciprocal altruism

In evolutionary biology, reciprocal altruism is a behaviour whereby an organism acts in a manner that temporarily reduces its fitness while increasing another organism's fitness, with the expectation that the other organism will act in a similar manner at a later time.

The concept was initially developed by Robert Trivers to explain the evolution of cooperation as instances of mutually altruistic acts. The concept is close to the strategy of "tit for tat" used in game theory. In 1987, Trivers presented at a symposium on reciprocity, noting that he initially titled his article "The Evolution of Delayed Return Altruism," but reviewer W. D. Hamilton suggested renaming it "The Evolution of Reciprocal Altruism." While Trivers adopted the new title, he retained the original examples, causing confusion about reciprocal altruism for decades. Rothstein and Pierotti (1988) addressed this issue at the symposium, proposing new definitions that clarified the concepts. They argued that Delayed Return Altruism was a superior term and introduced "pseudo-reciprocity" to replace it.

Theory

The concept of "reciprocal altruism", as introduced by Trivers, suggests that altruism, defined as an act of helping another individual while incurring some cost for this act, could have evolved since it might be beneficial to incur this cost if there is a chance of being in a reverse situation where the individual who was helped before may perform an altruistic act towards the individual who helped them initially. This concept finds its roots in the work of W.D. Hamilton, who developed mathematical models for predicting the likelihood of an altruistic act to be performed on behalf of one's kin.

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. 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:

the behaviour must reduce a donor's fitness relative to a selfish alternative; 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.

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

thumb|250px|[[Cleaning symbiosis: a small cleaner wrasse (Labroides dimidiatus) with advertising coloration services a big eye squirrelfish (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. 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. 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. There is difficulty and danger in finding a cleaner. Hosts leave their element to get cleaned.

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. 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.

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 selfish gene

Vampire bats

Vampire bats also display reciprocal altruism, as described by Wilkinson.

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.

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. However, vervet monkeys also display grooming behaviors within group members, displaying alliances. 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, This reciprocal altruistic behavior has been exploited by techniques designed to eliminate B. tryoni, which are fruit fly pests native to Australia.

Humans

Examples of reciprocal altruism in humans include helping injured individuals, sharing food, tools, or knowledge, 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, 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, and social contracts, where long-term benefits outweigh short-term costs. Additionally, studies in game theory, such as the Prisoner's Dilemma, illustrate how cooperative behaviors emerge and stabilize when individuals recognize the advantages of mutual support.

Exceptions

Some animals seem to be unable to develop reciprocal altruism. For example, pigeons defect instead of a random response or a tit-for-tat in a prisoner's dilemma game against a computer. This may be due to favoring short-term thinking over long-term thinking.

Regulation by emotional disposition

In comparison to that of other animals, the human altruistic system is a sensitive and unstable one. Therefore, the time or frequency of reciprocal actions contributes more to an individual's choice of partner than the reciprocal act itself.