Abstract
The evolution of social monogamy has intrigued biologists for over a century. Here, we show that the ancestral condition for all mammalian groups is of solitary individuals and that social monogamy is derived almost exclusively from this social system. The evolution of social monogamy does not appear to have been associated with a high risk of male infanticide, and paternal care is a consequence rather than a cause of social monogamy. Social monogamy has evolved in nonhuman mammals where breeding females are intolerant of each other and female density is low, suggesting that it represents a mating strategy that has developed where males are unable to defend access to multiple females.
Highlights
Despite extensive interest in the evolution of social monogamy stimulated by its prevalence in humans [1,2,3], its distribution in non-human mammals continues to puzzle evolutionary biologists [4]
We show that the ancestral condition for all non-human mammalian groups is of solitary females with males occupying separate but overlapping ranges; that the evolution of social monogamy has not been associated with a high risk of male infanticide and 20 that paternal care is a consequence rather than a cause of social monogamy
A recent comparative analysis [15] using a Bayesian approach identified six evolutionary transitions to monogamy in primates and concluded that social monogamy is derived from an ancestral condition where both sexes are social and live in unstable groups, supporting the suggestion that its evolution may be associated with the risk of male infanticide
Summary
Despite extensive interest in the evolution of social monogamy stimulated by its prevalence in humans [1,2,3], its distribution in non-human mammals continues to puzzle evolutionary biologists [4]. Male infanticide is typically found in species where the duration of lactation exceeds the duration of gestation [8, 31] but this is the case in relatively few socially monogamous species (20 of 75 species, 27%) compared to species where females are solitary (148 of 335 species, 44%; W=11733, p=0.34; phylogenetic independent 150 contrasts (pic) t=-1.63, p=0.10) and Bayestraits models provide no evidence of an association between the evolution of social monogamy and lactation durations that exceed gestation (lrt p>0.40, Table S2). The prevalence of male infanticide is lower among socially monogamous species (4 of 45 species, 9%) than among solitary species (24 of 88 species, 27%; W=1542.5, p=0.01), this difference does not appear to be a consequence of a direct 155 association between social monogamy and male infanticide, as analysis of phylogenetic independent contrasts (t=-0.402, p=0.69) and Bayestraits models suggest an independent evolution of the two traits (lrt p>0.90, Table S2). This difference does not appear to be a consequence of a reduction in 200 dimorphism after the transition to social monogamy, for the sequence of transitions as inferred by the most likely Bayestraits models suggests that social monogamy only evolved in species in which females are at least as large as males (lrt p
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