Monogamy with a purpose

Humans are fascinated by animal monogamy. In the 1960s, Konrad Lorenz idealized the lifelong pair-bonds of geese until one of his students pointed out some infidelities and suggested that geese may be “only human” (1), and Desmond Morris (2) speculated about the advantages of the pair-bond for early humans. Even though many theories have since been proposed, human monogamous inclinations have also been questioned, including the pervasive idea that it all boils down to provisioning by fathers. Frans B. M. de Waal. Sergey Gavrilets. Biologists prefer to place monogamy in a broad comparative perspective to determine what factors may have promoted its evolution. Why is monogamy ten-times more common in birds than mammals? Additionally, even though relatively common in primates, why are there no primates—other than humans—in which multiple reproductive pairs live together? Primate monogamy generally entails territoriality, with both the male and the female repelling outsiders of their own sex. Recently, two independent British teams have addressed these issues by analyzing variation in candidate traits that may have pushed species toward monogamy. Both studies used Bayesian and maximum-likelihood statistics to explore three traits: (i) paternal care, (ii) female sociality, and (iii) infanticide. The researchers used different databases, however. Kit Opie’s University College London team compared data on 230 primate species (3), whereas Dieter Lukas and Tim Clutton-Brock of Cambridge University covered no less than 2,545 mammalian species, including 330 primates (4). The teams further classified mating systems differently, with one team criticizing the classification of the other (4). The teams agreed on one …