Developmental psychologists identify propensities for social engagement in human infants that are less evident in other apes; Sarah Hrdy links these social propensities to novel features of human childrearing. Unlike other ape mothers, humans can bear a new baby before the previous child is independent because they have help. This help alters maternal trade-offs and so imposes new selection pressures on infants and young children to actively engage their caretakers’ attention and commitment. Such distinctive childrearing is part of our grandmothering (...) life history. While consequences for other cooperative activities must surely follow, the novel rearing environments set up by helpful grandmothering can explain why natural selection escalated preferences and motivations for interactivity in our lineage in the first place, and why, unlike other aspects of infant development, social sensitivities are not delayed in humans compared with genus Pan. (shrink)

The authors propose that many morbidities higher in women than men are adaptations protecting survival, selected because survival has been especially crucial to mothers' reproductive success. Following their lead, I pursue variation in tradeoffs between reproduction and survival recognized by Darwin that were likely central to the evolution of many traits that distinguish us from our great ape cousins.