In evolutionary biology, inclusive fitness is one of two metrics of evolutionary success as Hamilton's theory, alongside reciprocal altruism, is considered one of the two primary mechanisms for the evolution of social behaviors in natural species .. This goes along with the intuitive idea that you can't select for lower fitness. associated with inclusive fitness, to two simple models of reciprocal nation for the evolution of altruism among relatives based The relationship be-. Actually, the difference in mean inclusive fitness between the two groups of altruism systems by quantifying r, b, and c in association with kin.
On the same blood loci and from the same population, pairs of close male friends were significantly more similar to each other than were randomly matched pairs from the same sample Rushton, b.
A significant positive association between kinship and fertility was found by Helgason et al. In a study of twins, Kendler et al. In line with Hamilton's prediction, research finds that social assortment is more pronounced on the more heritable components measured within sets of homogeneous anthropometric, cognitive, and social characteristics.
In an experimental study of liking in acquaintances, Tesser manipulated people's beliefs about how similar they were to others on attitudes pre-selected as being either high or low in heritability.
He found that people liked others more when their similarity had been chosen by him on the more heritable items. A study of bereavement in twins found that MZ twins, compared to DZ twins: During debriefing, the participants expressed surprise that any morphing had occurred. DeBruine found people trusted a stranger's face more when it had been morphed with their own than when it was left unchanged. Familiarity was ruled out by using morphs of celebrities; only self-resemblance mattered.
DeBruine found that, although self-similarity of opposite-sex faces increased ratings of trustworthiness, it had no effect on ratings of attractiveness for a long-term partner and a negative effect on attractiveness for a short-term partner. When DeBruine et al. Putnam found that the more ethnically diverse a community, the less likely its inhabitants are to trust others, from next-door neighbours to local governments.
Inclusive fitness theory has been used to explain why members of ethnic groups move into the same neighbourhoods, join together in clubs and societies, and are prone to develop ethnocentric attitudes toward those who differ in dress, dialect, and other appearance.
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Irwin calculated coefficients of consanguinity within and between Eskimo tribes in the Hudson's Bay region of Canada and found prosocial behaviour such as wife exchange and anti-social behaviour such as the genocidal killing during warfare followed lines of genetic distance, albeit mediated by ethnic badging such as dialect and appearance.
Harpendinganalysed kinship within human populations. Because people have many more co-ethnics than relatives, the aggregate of genes shared with co-ethnics dwarfs those shared with extended families. Rather than being a poor relation of family nepotism, ethnic nepotism is virtually a proxy for it. In retrospect, it is not surprising that people are able to detect and prefer those who resemble themselves. Each individual gets a higher payoff from playing W than N, irrespective of what its opponent does—30 rather than 20 if the opponent plays W, 10 rather than 0 if the opponent plays N.
This captures a clear sense in which weak altruism is individually advantageous. In the context of evolutionary game theory, where the game is being played by pairs of organisms with hard-wired strategies, the counterpart of the fact that W dominates N is the fact that W can spread in the population even if pairs are formed at random cf.
To see this, consider the expressions for the overall population-wide fitnesses of W and N: Therefore, weak altruism can evolve in the absence of donor-recipient correlation; as we saw, this is not true of strong altruism.
So weak and strong altruism evolve by different evolutionary mechanisms, hence should not be co-classified, according to this argument. However, there is a counter argument due to D. Wilson, who maintains that weak altruism cannot evolve by individual selection alone; a component of group selection is needed.
Biological Altruism (Stanford Encyclopedia of Philosophy)
Wilson's argument stems from the fact that in a mixed W,N pair, the non-altruist is fitter than the weak altruist. More generally, within a single group of any size containing weak altruists and non-altruists, the latter will be fitter. So weak altruism can only evolve, Wilson argues, in a multi-group setting—in which the within-group selection in favour of N, is counteracted by between-group selection in favour of W. On Wilson's view, the evolutionary game described above is a multi-group setting, involving a large number of groups of size two.
Thus weak altruism, like strong altruism, in fact evolves because it is group-advantageous, Wilson argues. The dispute between those who regard weak altruism as individually advantageous, and those like Wilson who regard it as group advantageous, stems ultimately from differing conceptions of individual and group selection. For Wilson, individual selection means within-group selection, so to determine which strategy is favoured by individual selection, one must compare the fitnesses of W and N types within a group, or pair.
For other theorists, individual selection means selection based on differences in individual phenotype, rather than social context; so to determine which strategy is favoured by individual selection, one must compare the fitnesses of W and N types in the same social context, i.
Inclusive fitness - Wikipedia
These two comparisons yield different answers to the question of whether weak altruism is individually advantageous. Thus the debate over how to classify weak altruism is intimately connected to the broader levels of selection question; see NunneyOkasha, Fletcher and DoebeliWest et al.
Conceivably, an animal might engage in a social behaviour which benefits another and reduces its own absolute fitness in the short-term; however, in the long-term, the behaviour might be to the animal's advantage.
So if we focus on short-term fitness effects, the behaviour will seem altruistic; but if we focus on lifetime fitness, the behaviour will seem selfish—the animal's lifetime fitness would be reduced if it did not perform the behaviour. Why might a social behaviour reduce an animal's short-term fitness but boost its lifetime fitness?
By performing the behaviour, and suffering the short-term cost, the animal thus ensures or raises the chance that it will receive return benefits in the future. Similarly, in symbioses between members of different species, it may pay an organism to sacrifice resources for the benefit of a symbiont with which it has a long-term relationship, as its long-term welfare may be heavily dependent on the symbiont's welfare. From a theoretical point of view, the most satisfactory resolution of this ambiguity is to use lifetime fitness as the relevant parameter cf.
This stipulation makes sense, since it preserves the key idea that the evolution of altruism requires statistical association between donor and recipient; this would not be true if short-term fitness were used to define altruism, for behaviours which reduce short-term fitness but boost lifetime fitness can evolve with no component of kin selection, or donor-recipient correlation.
However, the stipulation has two disadvantages: Reciprocal Altruism The theory of reciprocal altruism was originally developed by Triversas an attempt to explain cases of apparent altruism among unrelated organisms, including members of different species.
Clearly, kin selection cannot help explain altruism among non-relatives. Trivers' basic idea was straightforward: The cost of helping is offset by the likelihood of the return benefit, permitting the behaviour to evolve by natural selection. For reciprocal altruism to work, there is no need for the two individuals to be relatives, nor even to be members of the same species.
However, it is necessary that individuals should interact with each more than once, and have the ability to recognize other individuals with whom they have interacted in the past. This evolutionary mechanism is most likely to work where animals live in relatively small groups, increasing the likelihood of multiple encounters. As West et al. Where reciprocal altruism is referred to below, it should be remembered that the behaviours in question are only altruistic in the short-term.
The concept of reciprocal altruism is closely related to the Tit-for-Tat strategy in the iterated Prisoner's Dilemma IPD from game theory.
In the IPD, players interact on multiple occasions, and are able to adjust their behaviour depending on what their opponent has done in previous rounds. There are two possible strategies, co-operate and defect; the payoff matrix per interaction is as in section 2.
The fact that the game is iterated rather than one-shot obviously changes the optimal course of action; defecting is no longer necessarily the best option, so long as the probability of subsequent encounters is sufficiently high. In their famous computer tournament in which a large number of strategies were pitted against each other in the IPD, Axelrod and Hamilton found that the Tit-for-Tat strategy yielded the highest payoff. In Tit-For-Tat, a player follows two basic rules: The success of Tit-for-Tat was widely taken to confirm the idea that with multiple encounters, natural selection could favour social behaviours that entail a short-term fitness cost.
Subsequent work in evolutionary game theory, much of it inspired by Axelrod and Hamilton's ideas, has confirmed that repeated games permit the evolution of social behaviours that cannot evolve in one-shot situations cf.
Nowak ; this is closely related to the so-called 'folk theorem' of repeated game theory in economics cf. Bowles and Gintis For a useful discussion of social behaviour that evolves via reciprocation of benefits, see Sachs et al. Despite the attention paid to reciprocal altruism by theoreticians, clear-cut empirical examples in non-human animals are relatively few HammersteinSachs et al.
This is probably because the pre-conditions for reciprocal altruism to evolve- multiple encounters and individual recognition—are not especially common. It is quite common for a vampire bat to fail to feed on a given night. This is potentially fatal, for bats die if they go without food for more than a couple of days.
On any given night, bats donate blood by regurgitation to other members of their group who have failed to feed, thus saving them from starvation. Since vampire bats live in small groups and associate with each other over long periods of time, the preconditions for reciprocal altruism are likely to be met.