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in social evolution may be alloparental care and unicoloniality in ants. Differences in kin recognition mechanisms also can have consequences for maintenance of advantageous genetic diversity within populations.

Seemingly overtly altruistic behavior, such as individuals accepting sterility, has puzzled evolutionary biologists since the time of Darwin. The first truly predictive framework for how reducing one’s own reproduction could be adaptive came from the seminal work of W. D. Hamilton (1964a). His key insight was that fitness is “inclusive” of both an individual’s direct reproduction and indirect gains arising through help provided to genetic relatives. Gains in indirect fitness, often labeled as “kin selection,” recast altruism as an ultimately selfish act. Help relatives if the benefit provided (b), prorated by the genetic relatedness of the recipient (r), exceeds the cost to self (c). This is Hamilton’s rule: Helping is adaptive if br > c.

More than any other taxonomic group, social Hymenoptera (ants, bees, and wasps) sit at an apparent peak of kin selection, with many species having morphologically sterile workers. Kin selection and applications of Hamilton’s rule, however, extend far beyond the evolution of sterile castes to examine many aspects of cooperative (and noncooperative) behavior (Bourke and Franks, 1995). Thus, social insects have had a pivotal role in the development of kin selection theory and its elevation to being the dominant evolutionary paradigm for the study of cooperation and conflict. To date, there have been hundreds of tests of kin selection predictions in social insects (Abbot et al., 2011). However, despite this track record of remarkable utility, kin selection theory has recently become embroiled in controversy. The mathematics of inclusive fitness modeling have been directly challenged (Nowak et al., 2010). The evolution of cooperation is argued as better explained by group-level selection than by nepotism toward kin (Wilson and Wilson, 2007). Finally, the status of social insects as being a paramount example of kin selection has been questioned, with kin selection relegated to being a dissolutive force that primarily selects against cooperation and sociality (Wilson and Hölldobler, 2005). The response to these criticisms from defenders of inclusive fitness modeling and kin selection has been simultaneously vigorous and dismissive (Foster et al., 2006; Lehmann et al., 2007; West et al., 2007c, 2008; Abbot et al., 2011; Herre and Wcislo, 2011; Strassmann et al., 2011b).

The current conceptual maelstrom offers an opportunity for a critical appraisal of the effects of kin selection in the social Hymenoptera. Considering a model or hypothesis as either a failure or success is highly subjective. No single model can be expected to be 100% accurate for all taxonomic groups and in all situations. It is nevertheless fair to categorize

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