Park or ride? Evolution of infant carrying in primates

Few mammalian orders carry their infants clinging to the mother's fur. I in vestigated the evolution of carrying behavior in primates and the life-hist ory and ecological correlates of infant care patterns. Primates are ideal f or the study as there is variation in infant care patterns. Primate infants are left hidden in nests or parked in trees, both of which strategies I te rm parking, and are carried orally or ride clinging to the mothers fur: rid ing. Infant carrying has evolved several times in the Primates and, once ev olved, it has been conserved. Significant energetic costs of riding are ind icated qs riding species maintain smaller home ranges than those of non-rid ers of the same body size. With body size and phylogenetic influences taken into account, riders appear to incur a reproductive cost by weaning and br eeding later than parkers. Although riders do not have lower birth rates th an those of parkers, their later age at first reproduction leads to their h aving a lower reproductive rate, measured by the intrinsic rate of populati on increase. Precociality of infants is not correlated with either riding o r nesting behavior. Although non-nesting species have larger litter sizes, their infants are not significantly smaller, nor are their neonatal brains relatively smaller. Although riding may have some energetic and reproductiv e costs, its repeated evolution in the Primates suggests that it also has s ome benefits, the most likely being a reduced mortality risk for carried in fants.