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Why reciprocal altruism is not a kind of group selection

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Abstract

Reciprocal altruism was originally formulated in terms of individual selection and most theorists continue to view it in this way. However, this interpretation of reciprocal altruism has been challenged by Sober and Wilson (1998). They argue that reciprocal altruism (as well as all other forms of altruism) evolves by the process of group selection. In this paper, we argue that the original interpretation of reciprocal altruism is the correct one. We accomplish this by arguing that if fitness attaches to (at minimum) entire life cycles, then the kind of fitness exchanges needed to form the group-level in such situations is not available. Reciprocal altruism is thus a result of individual selection and when it evolves, it does so because it is individually advantageous.

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Notes

  1. Whether that means they should best be interpreted as group selection is a matter with which we will not deal. It is also beyond the scope of this paper to deal with the related arguments for the unification of inclusive fitness and reciprocal altruism (e.g., Fletcher and Zwick 2006; Queller 1985).

  2. Consider the following scenario. By sequestering nitrogen and diffusing it into the soil a plant may make the very local environment better for its type. But because of the nature of seed dispersal in this species, say big seeds dispersed by wind, its nearest neighbors tend to be closely related. Therefore the benefit dispersed, nitrogen, is dispersed non-randomly with respect to kin and this trait can evolve by “kin group” selection. As Hamilton stressed, it is a mistake to think that kin selection requires any sort of kin recognition.

  3. Strictly speaking, the cognitive capacity is not a necessary condition for evolution of reciprocal altruism. Reciprocal altruism could evolve, for example, in extremely small populations where individuals have very few conspecifics to interact with (Axelrod and Hamilton 1981; Maynard Smith 1982), but such circumstances are far from the norm in nature.

  4. Our argument against reciprocal altruism being group selection thus differs from other challenges to Sober and Wilson, like Godfrey-Smith’s (2008) argument that with the appropriate neighborhood structure (but without groups sensu Sober and Wilson), altruism can arise. Skyrms (1994) makes the related and more general point that all one really needs is correlated interaction.

  5. More precisely, the smallest unit that fitness attaches to is the whole life cycle—fitness could attach to a unit greater than the individual life cycle and our argument would go through.

  6. Note that these equations assume that the altruist benefits everyone in the group equally, including itself. One certainly need not make that assumption. It is quite possible for the altruism to be distributed non-randomly within the group and have group selection still work (Brandon 1990). However, these equations describe the simplest case. They might well apply to the plant example described in note 2 above. Also they would apply to a case where alarm calls have some cost (increased chance of being noticed by the predator), but everyone in the group, including the caller, benefits (say by mobbing the predator).

  7. We should mention that S&W’s group selection model has been critiqued on many fronts. For example, some have argued that their models can be interpreted without invoking group selection (e.g., Gildenhuys 2003), while others have challenged the homogeneity of the category of group selection—see, e.g., the discussion of MLS1 and MLS2 in Okasha (2006). We are not here challenging the basic model of S&W, we are merely arguing that the group structure needed in their model is not present in reciprocal altruism.

  8. For example, Sober and Wilson (1998, 83) state the following: “Is it really fair to call a pair of individuals a group, especially if they interact only briefly with each other before departing, never to meet again? […] The duration of the group is left open in evolutionary game theory, which is sensitive only to the fitnesses of the ‘players’ that result from their interactions within the group. We therefore cannot object to calling an ephemeral group of size n = 2 a group, even though it is a far cry from the groups that Wright and Haldane imagined.”

  9. This way of understanding the relationship between fitness and altruism is not restricted to S&W; instead it is a standard way of defining altruism.

  10. For the sake of completeness, let us mention one other possibility that would save S&W’s position, namely setting the relevant group to be not the single interaction between R and A, nor the complete set of their interactions over their lifetimes, but rather a pair of interactions. The first interaction is the one we have described: A saves R from drowning. The second? When R saves A from drowning. But one difficulty here is that this second interaction may never happen. Furthermore, A and R may interact in a fitness affecting way, say, 53 times during their lives, the first five of which A plays the altruist role. So in this case, the suggestion is we would have to take interactions #1 and #6 and say that that constitutes a spatially and temporally discontinuous group. Again, what motivation might we have for this move? Only to save the position of S&W with respect to reciprocal altruism.

  11. Of course, since fitness is based on dispositions, not actual outcomes, the hustler’s tally is not a perfect indicator of the hustler’s fitness. Bad luck can occasionally quash even the best hustling strategy, after all.

  12. Overlapping generations are one of the difficult complications. Also, fitness in some cases may be dependent on a super-generational time scale (based on grandoffspring, not offspring, say). But none of the complications affect our basic point against S&W.

  13. It is for this reason that Evelyn Fox Keller (1987) argued that sexual reproduction involves group selection.

  14. Although our simple model does not have costs associated with searching for rare mate types, one could add the cost of a female, say, finding their appropriate male. Such costs would make it more realistic, but would not alter the basic point that we are making.

  15. Wilson (1978), for example, argued that most human altruism is reciprocal altruism and not group-selected altruism. Whether or not this is true, we think that it is a genuine empirical question.

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Acknowledgments

We wish to thank Charles Goodnight, David Sloan Wilson, and an anonymous referee for helpful critical comments on an earlier draft of this paper. A previous version of this essay was presented to the Duke Philosophy of Biology Reading Group—we thank them for their valuable discussion of our paper.

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Ramsey, G., Brandon, R. Why reciprocal altruism is not a kind of group selection. Biol Philos 26, 385–400 (2011). https://doi.org/10.1007/s10539-011-9261-7

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