Reciprocal altruism
Encyclopedia
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
.
, defined as an act of helping someone else although 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 person whom I helped before may perform an altruistic act towards me.
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. If chances of meeting another reciprocal altruist are high enough or the game is repeated for a long enough amount of time, this form of altruism can evolve within a population.
This is very close to the notion of "tit for tat
" introduced by Anatol Rapoport, 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.
Stephens shows a set of necessary and jointly sufficient conditions “… for an instance of reciprocal altruism:
There are two additional conditions necessary “…for reciprocal altruism to evolve:
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.
However, showing reciprocal altruism in an unambiguous way requires more evidence as will be shown later.
. Aside from the mutuality and the clear advantageous symbiosis
of the cleaner and the host, which cannot be interpreted in terms of altruism, the host displays some additional behaviour that meets the criteria for altruism:
The host allows the cleaner 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 may chase off possible dangers to the cleaner.
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 done by ecto-parasites.
Difficulty and danger in finding a cleaner. Hosts leave their element to get cleaned. Others wait no longer than 30 seconds before searching for cleaners elsewhere.
A key element in the establishment of reciprocal altruism is that the same two individuals interact repeatedly. This is conditioned by site specifics of either individuals (spatial condition) and by a large enough lifespan of the species (temporal condition).
Surprisingly there is sufficient evidence that individual cleaners and hosts indeed interact repeatedly.
This example meets the criteria that are described in Robert Trivers’ model.
However, some important elements, which are essential to establish reciprocity, are not yet shown:
The criterion that an individual doesn’t expect an immediate payment. In the cleaner-host system the benefit for a cleaner is always immediate.
The criterion that failing of one individual to act altruistically will cause the other one to avoid future altruistic acts. This will be very hard to show since such failure will mean death of the cleaner.
If Randall’s claim that the host may chase off possible dangers to the cleaner will be proved right, an experiment might be constructed in which reciprocity could be demonstrated.
It has been shown that predators learn specific localities and specialize individually on prey types and hunting techniques.
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.
Nevertheless, this presentation lacks important elements of reciprocity. It is very hard to detect cheaters. Also, there is no evidence that a bird refrains from giving calls when another bird is not reciprocating. And there is no evidence that individuals interact repeatedly.
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 bats feed each other by regurgitating blood.
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, 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 example for reciprocal altruism.
However, a closer look at the data shows that - except for a single interaction - all instances of feeding happened between individuals of the same group, who are on average cousins. Thus, it seems much more probable that this example is a case of kin selection
than reciprocal altruism.
According to Trivers the following emotional dispositions and their evolution can be understood in terms of regulation of altruism.
However, it is to be noted that there is no concrete explanation on how individuals pick partners because of the scarcity of theoretical and experimental researches that assess the importance of choice; theoretically, models indicate that evolution of behaviors associated with altruism involving partner choices rarely occur due to variability of costs and benefits between multiple individuals. . Therefore, it is believed that the time or frequency of reciprocal actions contribute more to an individual's choice of partner than the actual reciprocal act itself .
Robert Trivers
Robert L. Trivers is an American evolutionary biologist and sociobiologist and Professor of Anthropology and Biological Sciences at Rutgers University. Trivers is most noted for proposing the theories of reciprocal altruism , parental investment , facultative sex ratio determination , and...
to explain the evolution of cooperation as instances of mutually altruistic acts. The concept is close to the strategy of "tit for tat
Tit for tat
Tit for tat is an English saying meaning "equivalent retaliation". It is also a highly effective strategy in game theory for the iterated prisoner's dilemma. It was first introduced by Anatol Rapoport in Robert Axelrod's two tournaments, held around 1980. An agent using this strategy will initially...
" used in game theory
Game theory
Game theory is a mathematical method for analyzing calculated circumstances, such as in games, where a person’s success is based upon the choices of others...
.
Theory
The concept of “reciprocal altruism”, as introduced by Trivers, suggests that altruismAltruism
Altruism is a concern for the welfare of others. It is a traditional virtue in many cultures, and a core aspect of various religious traditions, though the concept of 'others' toward whom concern should be directed can vary among cultures and religions. Altruism is the opposite of...
, defined as an act of helping someone else although 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 person whom I helped before may perform an altruistic act towards me.
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. If chances of meeting another reciprocal altruist are high enough or the game is repeated for a long enough amount of time, this form of altruism can evolve within a population.
This is very close to the notion of "tit for tat
Tit for tat
Tit for tat is an English saying meaning "equivalent retaliation". It is also a highly effective strategy in game theory for the iterated prisoner's dilemma. It was first introduced by Anatol Rapoport in Robert Axelrod's two tournaments, held around 1980. An agent using this strategy will initially...
" introduced by Anatol Rapoport, 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.
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;
- the fitness of the recipient must be elevated relative to non-recipients;
- the performance of the behaviour must not depend on the receipt of an immediate benefit;
- conditions 1, 2, and 3 must apply to both individuals engaging in reciprocal helping.”
There are two additional conditions necessary “…for reciprocal altruism to evolve:
- A mechanism for detecting 'cheaters' must exist.
- A large (indefinite) number of opportunities to exchange aid must exist.”
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.
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
The first example is that of the cleaner fishCleaner fish
Cleaner fish are fish that provide a service to other fish species by removing dead skin and ectoparasites. This is an example of mutualism, an ecological interaction that benefits both parties involved. A wide variety of fishes have been observed to display cleaning behaviors including wrasses,...
. Aside from the mutuality and the clear advantageous symbiosis
Symbiosis
Symbiosis is close and often long-term interaction between different biological species. In 1877 Bennett used the word symbiosis to describe the mutualistic relationship in lichens...
of the cleaner and the host, which cannot be interpreted in terms of altruism, the host displays some additional behaviour that meets the criteria for altruism:
The host allows the cleaner 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 may chase off possible dangers to the cleaner.
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 done by ecto-parasites.
Difficulty and danger in finding a cleaner. Hosts leave their element to get cleaned. Others wait no longer than 30 seconds before searching for cleaners elsewhere.
A key element in the establishment of reciprocal altruism is that the same two individuals interact repeatedly. This is conditioned by site specifics of either individuals (spatial condition) and by a large enough lifespan of the species (temporal condition).
Surprisingly there is sufficient evidence that individual cleaners and hosts indeed interact repeatedly.
This example meets the criteria that are described in Robert Trivers’ model.
However, some important elements, which are essential to establish reciprocity, are not yet shown:
The criterion that an individual doesn’t expect an immediate payment. In the cleaner-host system the benefit for a cleaner is always immediate.
The criterion that failing of one individual to act altruistically will cause the other one to avoid future altruistic acts. This will be very hard to show since such failure will mean death of the cleaner.
If Randall’s claim that the host may chase off possible dangers to the cleaner will be proved right, an experiment might be constructed in which reciprocity could be demonstrated.
Warning calls in birds
Warning calls, although exposing a bird and putting it in danger, are frequently given by birds. An explanation in terms of altruistic behaviour is given by Trivers:It has been shown that predators learn specific localities and specialize individually on prey types and hunting techniques.
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.
Nevertheless, this presentation lacks important elements of reciprocity. It is very hard to detect cheaters. Also, there is no evidence that a bird refrains from giving calls when another bird is not reciprocating. And there is no evidence that individuals interact repeatedly.
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.
Vampire bats
Vampire bats also display reciprocal altruism, as described by Wilkinson.The bats feed each other by regurgitating blood.
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, 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 example for reciprocal altruism.
However, a closer look at the data shows that - except for a single interaction - all instances of feeding happened between individuals of the same group, who are on average cousins. Thus, it seems much more probable that this example is a case of kin selection
Kin selection
Kin selection refers to apparent strategies in evolution that favor the reproductive success of an organism's relatives, even at a cost to the organism's own survival and reproduction. Charles Darwin was the first to discuss the concept of group/kin selection...
than reciprocal altruism.
Known emotional dispositions as a complex regulating system for reciprocal altruism
The human altruistic system is a sensitive and unstable one. 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. 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.
- Friendship and emotions of liking and disliking.
- Moralistic aggression. A protection mechanism from cheaters acts to regulate the advantage of cheaters in selection against the altruists. The moralistic altruist may want to educate or even punish a cheater.
- Gratitude and sympathy. A fine regulation of altruism can be associated with gratitude and sympathy in terms of cost/benefit and the level in which the beneficiary will reciprocate.
- Guilt and repetitive altruism. Prevents the cheater from cheating again. The cheater shows his regret in order to save him from paying too dearly for his acts.
- Subtle cheating. A stable evolutionary equilibrium could include a low percentage of mimics in controversial support of adaptive sociopathy.
- Trust and suspicion. These are regulators for cheating and subtle cheating.
- Partnerships. Altruism with the purpose of creating friendships.
However, it is to be noted that there is no concrete explanation on how individuals pick partners because of the scarcity of theoretical and experimental researches that assess the importance of choice; theoretically, models indicate that evolution of behaviors associated with altruism involving partner choices rarely occur due to variability of costs and benefits between multiple individuals. . Therefore, it is believed that the time or frequency of reciprocal actions contribute more to an individual's choice of partner than the actual reciprocal act itself .
See also
- AltruismAltruismAltruism is a concern for the welfare of others. It is a traditional virtue in many cultures, and a core aspect of various religious traditions, though the concept of 'others' toward whom concern should be directed can vary among cultures and religions. Altruism is the opposite of...
- Competitive altruismCompetitive altruismCompetitive altruism is a possible mechanism for the persistence of cooperative behaviors, specifically those that are performed unconditionally. The theory of reciprocal altruism can be used to explain behaviors that are performed by a donor who receives some sort of benefit in the future...
- Gene-centered view of evolutionGene-centered view of evolutionThe gene-centered view of evolution, gene selection theory or selfish gene theory holds that evolution occurs through the differential survival of competing genes, increasing the frequency of those alleles whose phenotypic effects successfully promote their own propagation, with gene defined as...
- Iterated prisoner's dilemma
- Norm of reciprocityNorm of reciprocityThe norm of reciprocity is the social expectation that people will respond to each other in kind—returning benefits for benefits, and responding with either indifference or hostility to harms. The social norm of reciprocity often takes different forms in different areas of social life, or in...
- Reciprocal food sharingReciprocal food sharingReciprocal food sharing is a form of reciprocal altruism where one individual gives up the food it has forged to another individual. Food sharing has been observed in a wide range of animals, including insects, birds, cetaceans, vampire bats, and primates . It is not always an active behavior;...
- Reciprocity (evolution)Reciprocity (evolution)Reciprocity in evolutionary biology refers to mechanisms whereby the evolution of cooperative or altruistic behaviour may be favoured by the probability of future mutual interactions...
- SymbiosisSymbiosisSymbiosis is close and often long-term interaction between different biological species. In 1877 Bennett used the word symbiosis to describe the mutualistic relationship in lichens...
- Tit for tatTit for tatTit for tat is an English saying meaning "equivalent retaliation". It is also a highly effective strategy in game theory for the iterated prisoner's dilemma. It was first introduced by Anatol Rapoport in Robert Axelrod's two tournaments, held around 1980. An agent using this strategy will initially...
- Gift economyGift economyIn the social sciences, a gift economy is a society where valuable goods and services are regularly given without any explicit agreement for immediate or future rewards . Ideally, simultaneous or recurring giving serves to circulate and redistribute valuables within the community...