Families lend themselves well to the experimental analysis of adaptations, because almost every trait expressed in family life has a measurable effect on fitness. We have shown that many of these adaptations results from social evolution: this means that their function is to influence the fitness of another family member (e.g. Kilner et al 1999, Kilner et al 2004, Hinde et al 2007, Russell et al 2007, Kilner & Hinde 2008, Hinde et al 2010).
Thus animal families are animal societies in miniature. And, just as with any other sort of animal society, we have found that individuals in families may cooperate (Schrader et al in press, Cotter & Kilner 2010) but may also be in evolutionary conflict (Hinde et al 2010, Boncoraglio & Kilner 2012).
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Hinde, C. A. and Kilner, R. M. 2007 Negotiations within the family over the supply of parental care. Proc R Soc B 274:53-61
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Kilner, R. M. and Hinde, C. A. 2008 Information warfare and parent-offspring conflict. Adv. Stud. Behav. 38:283-336
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Schrader, M. et al 2015 Parental care masks a density-dependent shoft from mutually beneficial to competitive sibling interactions in burying beetle broods. Evolution in press