Comparative energetics of primate fetal growth

Among the primates, Homo sapiens has evolved a life history which includes long gestation, relatively slow growth to reproductive maturity, and large body size. While the slow growth rate may be linked to the energetic demands of having a large brain, there are other important morphological and physiological linkages that may be adaptive, including the development of significant fat stores with which to buffer against episodic and periodic energetic stress. In this comparative analysis of the energetic burden of pregnancy among primates (including humans), the daily energy investment in the development of neonatal tissue is modeled. During pregnancy, larger primates, notably the Hominidae, invest a smaller proportion of their maternal daily nonmaintenance energy budget in fetal tissue with increasing energy budget, allowing diverse adaptations, including foraging strategies which include folivory and mixed patterns of food getting, and meat consumption. Humans have a similar proportion of maternal daily nonmaintenance energy budget invested in fetal tissue with increasing energy budget to other apes and have a diet which is of much higher quality than predicted for body size and metabolic needs. The combination of high diet quality and low proportion of maternal daily nonmaintenance energy budget invested in fetal tissue allows greater brain size relative to body weight at birth compared with all other primates, apart from chimpanzees, and higher birthweight and body fatness at birth for a given body size than other primate species.