Mate guarding and the evolution of social monogamy in mammals

The majority of hypotheses proposed to explain the evolution of social monogamy focus on the benefits of biparental care to offspring (e.g., Kleiman, 1977; Wittenberger & Tilson, 1980). This is probably for two reasons. First, most socially monogamous fish, birds and mammals show some form of biparental care; indeed, this association is so close that many early authors included biparental care in their definitions of monogamy (e.g., Lorenz, 1963, p. 167; Lack, 1968, pp. 4-5; Brown, 1975, p. 168; Wilson, 1975, p. 589). Second, given the enormous difference that normally exists between the potential reproductive rates of the sexes (especially in mammals because of female gestation and lactation: Clutton-Brock & Vincent, 1991), it is difficult to explain why the most competitive males are unable to monopolize more than one mate, unless males are constrained by paternal commitments.