7 Reciprocal Altruism Examples

Reciprocal Altruism

What is Reciprocal Altruism?

Reciprocal Altruism refers to a behaviour of an organism to act in the favour of the other unrelated organism to increase its fitness at the cost of its own fitness. The organisms indulge in the act of reciprocal altruism with the hope that they will also receive help from the others in future. The important condition of reciprocal altruism is that the two individuals, i.e., the helper and the receiver should interact more than once with each other and they should recognize each other in future interactions. If there is only one interaction, i.e., they never meet in future this means there is no possibility of the return of the benefit. On the other hand, if the individuals interact repeatedly, they are capable of recognising the one who helped them in the past and those who did not. Individuals indulge in the act of reciprocal altruism with the one who helped them in the past and punishes the cheaters (who did not help in the past) by not providing them help. This shows that the reciprocal mechanism is more likely to occur among the animals that live in the small groups which increases the chances of repeated encounters.

Background of Reciprocal Altruism

The concept of reciprocal altruism was first discussed by an American sociobiologist and evolutionary biologist, Robert Trivers. He tried to explain the evolution of cooperation through the altruistic acts of the animals. Trivers told that originally in 1987, the title of his article was “The Evolution of Delayed Return Altruism” but according to the reviewer W.D Hamilton, this title was later changed to “The Evolution of Reciprocal Altruism.” The title of the article was changed but the examples mentioned in the manuscripts were still the same, this confuses the people about the accurate examples of reciprocal altruism. The researchers Rothstein and Pierotti contributed to this symposium in 1988 and tried to clarify this issue by proposing another definition of Altruism. They considered Delayed Returns Altruism (DRA) as a superior concept and replaced this term with pseudo-reciprocity. The study of Rothstein and Pietrotti did not receive much attention for some reason but it helped the other researchers to analyse the relationship between kin selection and altruism. Rothstein and Pierotti claimed that the examples mentioned by the Trivers in his article were the examples of the delayed return altruism and not of the reciprocal altruism.

Reciprocal Altruism vs Kin Selection

People often get confused between reciprocal altruism and kin selection because both the phenomena involve enhancing the fitness of the other organisms at the cost of their own fitness. However, these two concepts are different. The primary difference between the kin selection and the reciprocal altruism is that the kin selection is observed in the closely related organisms while the reciprocal altruism is observed in the unrelated organism. Reciprocal altruism was first described by Robert Trivers while the kin selection theory was described by Maynard Smith. Another difference is that in the case of reciprocal altruism an individual helps the other unrelated individual with the hope of receiving the help in the future from that individual while kin selection is a natural selection strategy where the closely related individuals help each other without the expectations of receiving any help from others in future. They help others only in the hope of the survival of their species.

Perhaps the most legitimately dispiriting thing about reciprocal altruism is that it is a misnomer. Whereas with kin selection the “goal” of our genes is to actually help another organism, with reciprocal altruism the goal is that the organism be left under the impression that we’ve helped; the impression alone is enough to bring the reciprocation” – Robert Wright

Following is a brief introduction of the researchers that helped in explaining the altruistic behaviour among the animals.

Reciprocal Altruism vs Kin Selection

Robert Trivers

Robert Trivers is a sociobiologist and evolutionary biologist who is popularly known for his contribution to reciprocal altruism. He mentioned the concept of reciprocal altruism in his paper ‘The Evolution of Reciprocal Altruism.’ He has also published papers on a variety of topics such as the sex ratio, parent-offspring conflict, parental investment and sexual selection, sex ratio in the social insects, and kinship. Trivers earned his bachelor’s degree in 1965, and he finished his PhD in 1972 from Harvard University. Later he worked as a biology professor at the University of California till 1994. His work in the field of evolution, especially the selfish gene theory has largely helped the other researcher in their studies. The selfish gene theory was originally formulated by Richard Dawkins. This theory describes that evolution can be explained through individual genes, i.e., each gene behaves in a particular way that ensures the chance of its survival by passing it to the next generation. This explains the concept of altruism too. According to the selfish gene theory, individuals indulge in sacrificial actions to benefit the closely related species of their offspring to ensure the passing on of their genes.

Robert Trivers

Robert Trivers

W.D. Hamilton

W.D Hamilton is one of the notable evolutionary biologists of his time. He is popularly known for proposing the kin-selection theory. Kin selection theory explains the altruistic behaviour among the animals by suggesting that animals help the other closely related species to ensure the survival of their species. This theory proposes that altruism is commonly seen in the closely related species rather than the unrelated species. Hamilton earned his bachelor’s degree from Cambridge University, and he pursued his further studies at the London School of Economics. Hamilton developed his popular theory of inclusive fitness at the London School of Economics. Hamilton is also known for formulating the mathematical model of Altruism, which is known as Hamilton’s rule. This mathematical model predicts the probability of the individual indulging in altruistic behaviour based on whether the individuals are closely related or unrelated.
W.D. Hamilton

W.D. Hamilton

Reciprocal Altruism and Iterated Prisoner’s Dilemma

Prisoner’s Dilemma is a game theory example that was originally framed by Melvin Dresher and Merrill Flood in 1950, but Albert W. Tucker, an American Mathematician formalized it and titled it “prisoner’s dilemma.” Following is the version of the prisoner’s dilemma mentioned by an author William Poundstone in his book titled ‘Prisoner’s Dilemma,

Two members of a criminal gang are arrested and imprisoned. Each prisoner is in solitary confinement with no means of speaking to or exchanging messages with the other. The police admit they don’t have enough evidence to convict the pair on the principal charge. They plan to sentence both to a year in prison on a lesser charge. Simultaneously, the police offer each prisoner a Faustian bargain.”

Following are the possible outcomes,

  • If Prisoner A and Prisoner B both betray, both will go to jail for two years.
  • If Prisoner A betrays the other but Prisoner B does not confess, Prisoner A goes free while Prisoner B will go to jail for three years.
  • If Prisoner A do not confess, but Prisoner B betrays Prisoner A and confesses, Prisoner A will have to go to jail for three years and Prisoner B goes free.
  • If both prisoner A and Prisoner B do not confess, both have to go the jail for one year only.

Reciprocal altruism is closely related to the concept of the Tit-for-Tat strategy of the Game Theory’s iterated Prisoner’s Dilemma. The iterated prisoner dilemma is the extended version of the above prisoner’s dilemma. In this version, the above game is played between the same prisoners multiple times. This allows the prisoners to choose their decisions in the future rounds based on the decisions of the other players in the previous rounds. The two possible tactics that the player can use in the iterated Prisoner’s Dilemma are, co-operate and defect. The payoff matrix as per the number of interactions of the players is represented below in figure A. In this game defecting may not be a suitable option as the likelihood of future encounters is high. According to the evolutionary biologist Robert Axelrod and William D. Hamilton, to get the highest payoff, the Tit-for-Tat strategy is the best. The two basic rules of the Tit-for-Tat strategy are,

i. The players should cooperate in the first encounter.

ii. Make decisions based on the behaviour and the decision of the other player in the subsequent encounters.

The work on the evolutionary game theory by Axelrod and Hamilton shows that repeated behaviour allows the evolution of social behaviour which does not happen in the games that have one-time interactions.

Pay-Off Matrix of Prisoner's Dilemma

Figure A

Reciprocal Altruism Examples

1. Red-Winged Blackbird Male

The red-winged blackbird male is known for defending the nests of its neighbours. Various researchers explain this behaviour of the red-winged blackbird through different theories. Some explain this by suggesting that the bird defends only those nests which consist of their extra-pair offspring. Extra-pair offspring are likely to contain some DNA from the male bird. Another explanation is that males help the closely related males only. The Department of the Fisheries and Wildlife explains the behaviour of the blackbird males through the tit-for-tat strategy. The research was conducted to analyse the behaviour of the male birds when the different types of nests were used. They looked for the behaviour like the frequency of the calls, strikes and dives. When the result was analysed it was found that the kin selection was not observed. When the extra-pair offspring were present in the nests it did not impact the frequency of the male bird in defending the nest. But, the frequency of the male bird defending the nests reduced when they realised that the neighbour males has reduced the defence for their nests. This shows the tit-for-tat strategy, i.e., the animals help only those who have helped them in the past. This shows that it is an example of reciprocal altruism.

Red-Winged Blackbird Male

2. Vampire Bats

Biologist Dr GS Wilkinson described that vampire bats also show reciprocal altruism. Vampire bats generally live in the colonies. They survive by feeding on the blood of animals like pigs, horses and cattle. The research was conducted at the University of California, San Diago to study the reciprocal altruism among the vampire bats. In this research, some of the vampire bats of the colony were well-fed while some of them were kept hungry. It was observed in this experiment that the well-fed vampire bats shared the regurgitated blood with the hungry vampire bats. It is to be noted that bats can not survive more than 70 hours without eating, hence the regurgitated blood received by the hungry bats from the well-fed bats was crucial to saving the lives of the hungry bats. According to the reciprocal altruism model of Trivers, an act can be called reciprocal altruism only if the benefits received by the receiver are more than the cost to the donor. This condition seemed to be satisfied in this example because if the bats were not fed by their fellow members they were likely to die within just two days. Another eligibility of an act to be considered the reciprocal altruism that the individual who helped the other in the past also helps the helper in the future is also met by this phenomenon. Vampire bats help their fellow members by sharing the food with the ones who had helped them in the past. There are also numerous examples available that show that vampire bats usually regurgitate blood for the other members of the group who were not able to get the food for some reason.

Altruism in Vampire Bats

3. Cleaner Fish

Cleaning symbiosis can be considered a perfect example of reciprocal altruism. Cleaning symbiosis refers to a mutually beneficial act between the individuals belonging to the different species, where one individual cleans the surface of the other individual by removing or eating the parasites. Let us understand this with the example of the cleaner fish and the host organisms. Although the symbiosis of the host and the cleaner is apparent which may make you think that it is not an act of altruism, the additional behaviour shown by the host is what makes it an act of reciprocal altruism. The host fish provides a safe entry and exit for the cleaner fish to its mouth for cleaning, and even after the cleaning is done host fish allows the cleaner fish to leave instead of eating it. The host fish even sometimes protect the cleaner fish from the possible dangers. It is observed that when the host fish is attacked by the predators while the cleaner fish is cleaning the mouth of the host fish, the host fish first allows the cleaner fish to come out of the mouth and then it fights with the predator instead of swallowing the cleaner fish. Cleaning from the cleaners is necessary for the host because otherwise, the host is likely to suffer from injuries due to ectoparasites. Hence, sometimes the host even undergoes various difficulties to find a cleaner. The frequent interaction between the same two individuals, i.e., the host and the client is the essential requirement for reciprocal altruism. For this to happen, the cleaner and the host should remain in the same locality or area so that they can frequently interact. The act won’t be considered reciprocal altruism if the host eats the cleaner after the cleaning is done. There is a number of examples cited by the researchers that shows that the hosts and cleaners do interact frequently. This phenomenon is observed in the other animals too, for example, birds and shrimps act as cleaners and organisms like octopus, mammals, turtles, and fish acts as clients. However, The example of the cleaner-host system does not meet all the criteria of reciprocal altruism as mentioned in Triver’s model. Rothstein and Pierotti considered it an example of delayed return altruism.

Cleaner Fish

4. Bacteria

Various examples show that some species of bacteria also show reciprocal altruism towards the other species. Generally, the reciprocal altruism act involves the one form of bacteria supplying the important nutrients to the other species and the other species providing a suitable environment for the bacteria to survive. The nitrogen-fixing bacterias and the plant species in which they survive is also an example of reciprocal altruism. Also, certain species of flies like Bactrocera tryoni and some bacteria show reciprocal altruism. The flies eat the nutrient providing bacteria, which are found on the plant’s leaves, and in return, these bacteria reside in the digestive system of the flies.

5. Warning Calls by Birds

On the attack of the predators, some birds usually give warning calls to the other closely related or unrelated animals to signal them about the danger. While doing so the birds themselves put their life at risk as they grab the attention of the predators towards themselves. Trivers tried to explain this as follows:

It is observed that predators learn about particular localities and specialize in their hunting techniques. This means that the whole bird locality is at a disadvantage if the predators attack their conspecific because the predator will become capable of attacking them also in future. Hence, they give warning calls so that the predator won’t be able to specialize the way to hunt the species belonging to their locality. This shows that the areas where the birds give the warning calls have a selective advantage over the areas in which no such warning calls are given by the birds. However, this example does not meet all criteria of reciprocal altruism. There is not any evidence that shows that a bird stopped giving warning calls because another bird did not give the warning calls, also there is not any evidence of their repeated interaction with them. This phenomenon can also be explained that maybe these are not the warning calls, maybe these are the calls to the predator by the bird when it was detected by the predator to signal that there is no use in wasting the time on attacking the calling bird. This hypothesis can be supported by the following two facts,

  • The frequency of the warning calls given by the birds matches the hearing range of the bird of prey.
  • It is generally observed that the calling birds are not much attacked by the predator bird, predator birds mostly attack the other birds.

Warning Calls by Birds

6. Primates

Some studies reveal that the habits of the primates of grooming others, meet the requirement of reciprocal altruims. A study on the Vervet monkeys revealed that they are more responsive to the helping calls of unrelated individuals in case of the grooming aid. Vervet monkeys generally indulge in grooming acts among the members of the group. This shows that the grooming behaviour of the vervet monkeys is a part of the kin selection because this behaviour is largely observed among the siblings according to a study.

7. Bees

Bees’ acts can also be considered as an example of reciprocal altruism. Bees fly to different flowers to collect the nectar that they require to make honey. While doing this process, the pollen from a flower gets collected in the body of the bees, when the bee jumps to another flower the pollen gets transferred to another flower resulting in the pollination. This process involves mutual benefits as the bees collect the nectar and flowers get pollinated. This can also be termed mutualism or mutualistic symbiosis.

Reciprocal Altruism in Bees

Reciprocal Altruism & A Complex Regulating System

The natural selection process should favour a complex regulating system or psychology in each individual to function the reciprocal altruism. This involves regulating the tendency of the individual to give or cheat, and the way the individual responds to the other’s actions of giving and cheating. Following are some of the important factors that guide reciprocal altruism.

Moralistic Aggression

Cheaters (individuals who do not help back) tend to take advantage of altruistic behaviour, and natural selection has developed a protective mechanism among individuals, called moralistic aggression. This mechanism compels the altruist to change their decision rather than selflessly performing the altruistic acts for the offender. This mechanism may compel individuals to even isolate or exile the offenders.


The tendency of the person to like others and make friendly relationships with the likeable people motivate the people to indulge in altruism.


The act of reciprocity ends in the case of cheating by an individual. Guilt is the natural selection process that pressurises the cheater (who did not help back) to feel bad about their deed and convince others that cheating won’t be repeated in future. This means that guilt motivates people to compensate for their cheating behaviour by indulging in reciprocal altruism in future. Guilt prevents disruptions in the relationship between the helper and the receiver. Some also suggest that certain psychological issues like depression act as a mechanism to enhance reconciliation and cooperation among individuals.

Gratitude and Sympathy

Feeling sympathy towards someone suffering from pain and feeling gratitude influence altruism in an individual.

Subtle Cheating

An individual may influence other people for his/her own advantage by imitating altruistic behaviour. The acts of subtle cheating include fake guilt, fake sympathy, and fake moralistic aggression.


Altruistic acts can result in the development of friendships among individuals, which eventually result in reciprocity. One can also induce friendship towards strangers or enemies by showing altruistic behaviour.


Natural selection favours the individual’s ability to identify moralistic aggression. The ones who indulge in altruism without feeling the emotions like guilt or generosity tend to be less reliable than the ones who indulge in altruism due to the emotional basis.

Developmental plasticity

Developmental plasticity refers to the occurrence of neural pattern changes, physiological changes, behavioural changes and anatomical changes in an individual due to the gene-environment interactions during their development. The development of an individual is affected by various external and internal factors. As different places have different social and ecological conditions this may impact the developmental plasticity of the cheating behaviour and altruistic behaviour belonging to the different areas. People tend to learn about altruism and cheating behaviour from their environment, particularly from kin. If in a particular region more focus is given to educating about the guilt, this will discourage the cheating behaviour among the people belonging to that region, and reciprocity will be observed more.

Multiparity Interaction

In the areas where the individuals live in small and closely related groups, one can easily learn from the altruistic and cheating acts of the others members of the group. People can form some rules to act upon the ones who cheat, i.e., the one who does not show reciprocity.

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