Reciprocal Altruism

The Basic Idea

Let’s be honest here. You’ve probably covered for a friend or sibling while they snuck out to a party past curfew. When you agreed to this scheme, what was the first thing that crossed your mind? Maybe you thought “this is a stupid idea, I could get in trouble”. But maybe the gears started turning: “If I do this right now, they’ll help me out in the future.”

This idea of making a sacrifice to receive a later payment is known as reciprocal altruism. While altruistic behavior is characterized as making sacrifices for others due to our care for their well-being, reciprocal altruism occurs when an individual acts altruistically in hopes of equal-value repayment in the future.1, 2

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

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Key Terms

Altruism: Acting in such a way that incurs a cost from oneself and benefits another.1

Reciprocal Altruism: A behavioral strategy in which an agent sacrifices for the benefit of a recipient who is not closely related, where a return benefit to the agent may be reciprocated in the future.3, 4

Cheater: Within the context of reciprocal altruism, a cheater is someone that is always on the receiving end of altruistic behaviors from others but never reciprocates.


While British Naturalist Charles Darwin’s theory of evolution was first introduced to the public in 1859, it maintained a very controversial image up until the 1950s. During that time, a point of debate was the unexplainable observation of altruistic behavior in nature. According to Darwin’s evolutionary logic, individuals only engage in behaviors that increase their own survival and the probability of their offspring’s existence and survival. Thus, the theory could not account for observations of unrelated individuals engaging in behaviors where the actor incurs a cost and the recipient a benefit, with regards to reproductive success.

Reciprocal altruism saw early beginnings with Egyptian-born British evolutionary biologist W.D. Hamilton in 1964, when he developed mathematical models to explain the evolution of altruistic behavior within populations based on the degree of relatedness.3, 5

In 1971, American evolutionary biologist Robert Trivers countered the problem of contradictory altruistic behavior through a series of papers, which became the foundation for modern evolutionary psychology. Within these papers, Trivers introduced the ecological conditions in which altruistic behavior was more likely to occur as an adaptive strategy to increase survival and reproductive success. These conditions required individuals to be long-lived, have low dispersal rates, and live within a small, mutually-dependent, and stable environment with parental care. This would optimize for the number of opportunities to display reciprocity.3, 4

There were two crucial conditions for this model: the cost to the actor must be less than the benefit to the recipient in terms of reproductive success, and everyone involved must continuously monitor these interactions. Through consistent monitoring, one can catch cheaters or those who do not reciprocate altruistic acts. Trivers believes that once caught, cheaters will be punished and will no longer be the recipient of altruistic actions. Eventually, cheaters will suffer more than they would have if they had initially reciprocated.3, 4


Robert Trivers

Robert Trivers is an evolutionary biologist, primarily known for his work with reciprocal altruism. He has also published papers on the topics of: parental investment and sexual selection, the sex ratio, parent-offspring conflict, kinship and sex ratio in the social insects, and of course, reciprocal altruism in his paper titled The Evolution of Reciprocal Altruism. Trivers received his bachelor’s degree and PhD from Harvard in 1965 and 1972, respectively, and then moved to the University of California, Santa Cruz, to work as a biology professor until 1994. His recent work has veered towards the realm of genetics, specifically the selfish gene theory.6

W. D. Hamilton

One of the most prominent evolutionary biologists of our time, William Donald Hamilton’s theory of kin selection has greatly influenced the study of social behavior, demonstrating that altruistic behavior is more likely to be seen towards relatives compared to unrelated individuals. He received his bachelor’s degree in genetics from Cambridge University, and continued his graduate studies at the University of College London and London School of Economics, where he developed his famous inclusive fitness theory. Hamilton is also recognized for developing the mathematical model appropriately named Hamilton’s rule, which predicts the likelihood of altruistic behavior based on degrees of relatedness between individuals.7


The interactions involved in reciprocal altruism can be mapped out within a traditional prisoner’s dilemma matrix. Originally conceived by mathematicians Merrill Flood and Melvin Dresher in 1950, this model was invented to represent different outcomes depending on whether two individuals cooperated or acted solely for their own interests.

Within the prisoner’s dilemma, both participants have two choices: to cooperate or not cooperate. This creates three possible scenarios: If one cooperates and the other does not, then the former benefits greatly while the latter suffers. If neither cooperates, then neither face extreme consequences. However, both would fare much better if they had both cooperated, which is the most optimal outcome overall. Traditionally, the prisoner’s dilemma makes the assumption that each participant is acting only for their own benefit, thus coming to the conclusion that both participants will act uncooperatively. This leads to both participants not benefitting as much as they could if they had just both cooperated.

The prisoner’s dilemma fits into reciprocal altruism if we make the assumption that participants face an infinite amount of rounds. This is known as the iterated prisoner’s dilemma. Israeli mathematician Robert J. Aumann found that under this new assumption, a cooperative outcome would be possible. So long as both participants start by picking the cooperative move (engaging in reciprocal altruism) and continue to do so, this cooperative behavior will remain present in the participants’ dynamic. This is known as “tit-for-tat”: participants will continue to reciprocate what the other participant did on their last move, only choosing not to cooperate once a participant has been betrayed themself. In terms of reciprocal altruism, the iterated prisoner’s dilemma tells us that one will continue to exhibit altruistic behavior until the recipient does not display the same behavior back.8, 9

As one can imply from the history of reciprocal altruism, it has many applications in the field of evolutionary biology. The selfish gene theory is an example of such. Created by British evolutionary biologist Richard Dawkins, the selfish gene theory dictates that the basis of evolution is the individual gene. This means each gene acts in such a way that it has the best chance of being replicated and passed on to the next generation. This is where altruistic behavior comes into play. The selfish gene theory states that one would perform sacrificial actions for the benefit of their offspring so that their genes will get passed on.

Reciprocal altruism isn’t unique to humans, it is found between other species in nature as well.  Bees, for example, fly from flower to flower to collect nectar which they use to make honey. During this process, pollen is collected in the bodies of the bees at one flower and rubs off onto another, pollinating the flowers. This is mutualistically beneficial, as the bees get to eat and the flowers get pollinated. This is also known as a mutualistic symbiosis or simply mutualism.10


If we take a closer look at the definition of altruism, a mandatory condition is that the sacrificial behavior exhibited is done selflessly, meaning the do-gooder is not expecting anything in return. This contradicts the definition of reciprocal altruism, which implies the do-gooder is expecting the recipient to reciprocate an equal value action in the future. So which altruism is correct: true altruism or the reciprocal form?

According to psychological egoism, reciprocal altruism is the only altruism that can occur. This philosophical view suggests the source of all human motivation is purely self-interest. However, this does not mean that we do not perform actions to benefit others. A psychological egoist would say that we engage in behavior that benefits others, but only because we think helping others increases our own well-being, and not for the other person’s sake. Thus, according to psychological egoism’s beliefs, true altruism does not and cannot exist.11

Case Study

Tourism and reciprocal altruism

On the surface, it seems that the only cooperative relationship between a tourist and a host country is that of the economic agenda. However, researchers in this study claim that cooperation, defined as a long-term relationship based on reciprocity and altruism, should not be occurring in tourism because of the short-term nature of tourism. They go through a series of interaction scenarios between tourists and hosts to demonstrate why, from a socio-biological perspective, the cooperative response is not ideal.

The one-shot reciprocity scenario goes as follows: the tourist pays a fee to the host, who is the service provider. They receive this payment as a benefit. However, for the host to provide this service to the tourist, they must be subjected to a cost themselves for their time, equipment, etc. Although both parties involved incur costs and benefits, the one-shot nature of this event allows for cheating. Given that the host will likely never see the tourist again in their lifetime, there is nothing preventing them from withholding premium-quality service, at the expense of the tourist.

Imagine you are on vacation in Rome and have joined a tour group led by a local. You’ve prepaid for this experience, so there is no incentive for the tour guide to actually provide you with the experience they claimed since they have received the full payment beforehand. So instead of leading your tour group to a local bar that has the best drinks in town for a cheap price, they bring you to an expensive bar with mediocre drinks since it is less out of the way, or they have a deal with the bartender, or another sneaky reason – since tourists wouldn’t know any better.

Researchers suggest that sustained selfishness in place of cooperation could be a solution to this problem. Not only would tourists be helping other tourists that come into contact with the same host, but they would also be helping themselves under the assumption and expectation that another tourist before acted altruistically for their benefit.

For example, tourists who have received a tour from a certain company are able to put reviews online about their experience and discuss with other tourists who also received the same tour from the same company about how they felt about the experience and share their ratings for others to see.12

Related TDL Content


Want to hear more about true altruistic behavior, without the expectation of reciprocation? Read this reference guide to find out more about sacrifice solely for the sake of another’s well-being.

Prisoner’s Dilemma

A foundational concept in behavioral economics, the prisoner’s dilemma is an easy-to-understand and very applicable concept to our understanding of predicting human behavior. Read this reference guide to find out how economics predicts whether humans choose to cooperate or act selfishly.


  1. Altruism. The Decision Lab. (n.d.).
  2. Segerstrale, U. (2016, April 21). Sociobiology, history of. Encyclopedia of Evolutionary Biology.
  3. Jacobson, A. (2016). Reciprocal altruism. Encyclopedia of Evolutionary Psychological Science, 1–2.
  4. Trivers, R. L. (1971). The evolution of reciprocal altruism. The Quarterly review of biology, 46(1), 35-57.
  5.  Hamilton, W. D. (1964). “The Genetical Evolution of Social Behavior II”. Journal of Theoretical Biology. 7 (1): 17–52. doi:10.1016/0022-5193(64)90039-6. PMID 5875340.
  6.  Trivers, R. (n.d.). About Me. Robert Trivers.
  7.  Moran, N., Pierce, N. & Seger, J. W.D. Hamilton, 1936–2000. Nat Med 6, 367 (2000).
  8. Prisoner’s dilemma. The Decision Lab. (n.d.).
  9.  Krams, I. (2016). Reciprocal altruism (middle-level theory in evolutionary psychology). Encyclopedia of Evolutionary Psychological Science, 1–10.
  10. Mutualistic relationships. New England Complex Systems Institute. (n.d.).
  11.  Kraut, R. (2020, August 31). Altruism. Stanford Encyclopedia of Philosophy.
  12. Fennell, D. A. (2006). Evolution in tourism: The theory of reciprocal altruism and tourist–host interactions. Current Issues in Tourism9(2), 105–124.

About the Author

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Adrienne Fu

Adrienne Fu is a student at McGill University studying Economics, Computer Science, and Psychology. She is passionate about behavioural economics, particularly its intersection with consumer decision-making and UX Design. Outside of the (virtual) office, she enjoys film photography, reading, and taking care of her (many) plants.

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