In the Light of Evolution Volume V: Cooperation and Conflict (2011) / Chapter Skim
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1 Expanded Social Fitness and Hamilton's Rule for Kin, Kith, and Kind--DAVID C. QUELLER
1 Expanded Social Fitness and Hamilton's Rule for Kin, Kith, and Kind--DAVID C. QUELLER
Pages 5-26
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From page 5... ...
It involves social effects of a trait that affect a partner, with feedback to the actor's fitness. I derive expanded versions of Hamilton's rule for kith and kind selection, generalizing Hamilton's insight that we can model social selection through a sum of fitness effects, each multi plied by an appropriate association coefficient.
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From page 6... ...
I will also argue that it is often worth distinguishing kin and kith selection from what I call kind selection, partly to properly capture social causality and partly because these forms of social selection act in very different ways. Inclusive fitness, developed by Hamilton (1964a)
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From page 7... ...
First, it covers more kinds of social selection or at least, it covers more in a causal manner. Second, it expands out into the number of terms needed to describe this causation with two kinds of distinct terms: selection terms relating social actions to fitness components and associa tion coefficients that essentially describe the relative heritability of those effects.
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From page 8... ...
, which is further developed for social traits in the indirect genetics effects approach (Moore et al., 1997; Bijma and Wade, 2008; McGlothlin et al., 2010)
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Therefore, proponents of inclusive fitness can rightly refute the claim of limited generality. However, one of the main appeals of inclusive fitness is that it can often be used without knowledge of the genes, and therefore, we will consider the phenotypic gambit shortly.
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Why then do we prefer the inclusive fitness result? The first reason, to be treated shortly, is that leaving out the partner does not work when we try to play the phenotypic gambit.
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When kin are affected, the phenotypic gambit requires indirect effects. If we use only the actor's phenotype P to model its fitness (W = α + βWPP + ε)
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Then, relatedness is essentially the ratio of the actor's breeding value when the partner performs the behavior to its breeding value when the actor performs the behavior. Switching this neighbor-modulated version to inclusive fitness gives Cov(G, P')
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From page 13... ...
Kith selection, in contrast, requires phenotypic expression by the partner. The focal individual can affect its own fitness in kith interactions only through feedbacks.
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From page 14... ...
Expression (10) is an expanded version of Hamilton's rule that captures kith selection, but it is a neighbor-modulated form, with effects on a focal actor rather than an inclusive fitness form that attributes all effects to a focal actor.
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From page 15... ...
and the fitness of its partner (βW′P) , with the latter multiplied by a feedback coefficient of βWW′∙P that describes how much partner's fitness affects the actor's fitness, partialing out the nonsocial effects of the actor's behavior (which are included in the first term)
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From page 16... ...
. Table 1.1 shows many differences between greenbeard or kind selection relative to kin selection (and also, for completeness, to kith selection)
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From page 17... ...
The situation with greenbeards is more com plex. An altruistic greenbeard allele is related by r = 1 to its beneficiaries and therefore may give more aid compared with what would be favored at other loci not related to that degree.
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However, kin selection models with costs and benefits that are nonadditive typically show frequency dependence. I will argue below that this is because these nonadditive models include a form of kind selection.
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From page 19... ...
They are frequency dependent and nonadditive, but those terms do not capture the reason why the process works (the way kin selection does for affecting relatives)
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Thus, the d term here is negative, representing an antigreenbeard effect of harm ing one's own type. A negative d means negative frequency dependence, with strategies being more favored when rare, leading to the possibility of polymorphism.
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Frequency-dependent effects are often incorporated into direct fitness. Greenbeard effects, in contrast, are usually attributed to indirect fitness through the partner.
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From page 22... ...
Adding P × P′ as a predictor allows us to fit those points and explain more of the vari ance. However, more importantly, the simpler versions can sometimes be incorrect, biased in the same way that caused us to reject the simple direct fitness model in favor of inclusive fitness.
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From page 23... ...
These expanded social fitness results, like the tradi tional ones, separate out two kinds of distinct terms: selection terms relat ing social phenotype to fitness components and relative heritability terms that derive from associations of genes and phenotypes, or just phenotypes. The model suggested here stakes out a middle position between standard inclusive fitness theory and more complex models (e.g., from population genetics)
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From page 24... ...
Kind effects are a bit more complex. The strictly genetic form of standard inclusive fitness (6)
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From page 25... ...
ACKNOWLEDGMENTS I thank Francisco Ayala and John Avise for helping to organize the National Academy of Sciences Sackler symposium on cooperation and conflict. For comments on the manuscript, I thank two anonymous referees, Joan Strassmann, Michael Whitlock, Stuart West, Kevin Foster, Claire El Mouden, and the Oxford Social Evolution Group.
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