Do Bigger Brains Mean Better Milk

Life history theory proposes that individuals have a finite amount of energy that can be spent on either growth or reproduction, leading to a trade-off between fecundity and survival to maturity (Charnov 1993; Purvis et al. 2003; Stearns 1992). The subsequent pace of a species’ life history reflects the trade-off between the potential gains for continuing to grow larger and the risk of dying before reproducing (Charnov 1993). The variation in the pace of life history strategies across mammals reflects the myriad ways in which energy can be partitioned to maximize fitness over the lifetime. On one end of the continuum of life history variation are primates who have been described as living “life in the slow lane” (Charnov and Berrigan 1993). As a result of their protracted life history strategy, primate mothers invest more heavily in each offspring during gestation and lactation compared to non-primate mammals (Dufour and Sauther 2002; Martin and MacLarnon 1990). However, because this investment is paid out over a longer period of time, the daily energetic burden of primate reproduction on the mother is relatively low (Dufour and Sauther 2002; Martin and MacLarnon 1990).