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The Only Flame in Town
Unusual for mammals, humans are notably socially monogamous, with pair bonding sometimes lasting decades. Why? Lukas and Clutton-Brock (p. 526; see the Perspective by Kappeler) examined data from over 2500 mammalian species across 26 orders containing 60 evolutionary transitions to monogamy. In every case, the ancestral condition was one where females were solitary and where male infanticide was unusual. Monogamy appears to arise not as a response to a need for paternal care, but largely as a mate-guarding strategy.
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.