Grandmothers and their consequences

pre-printBoth what we share and don't share with our primate cousins make us human. Easy enough to start a list. At least since Darwin, most would rate moral sentiments as distinctively human. But our modern selves didn't emerge from ancestral apes in one step. When did populations along the way become human? Before our big modern brains, before language, and before pair bonds, our longer lives, later maturity, and earlier weaning could have evolved in an already smart and gregarious ancestor due to rearing help from grandmothers. Although cooperative hunting and lethal between-group aggression are often nominated as evolutionary foundations for human prosociality, neither distinguishes us from chimpanzees. Grandmothering does. Our grandmothering life history intensified selection on infant appetites and capacities for social engagement, the foundation of our moral faculties