I read this on the plane the other day:
Taylor endorses Wrangham’s hypothesis but believes it is not enough. Not only is our brain very large, it is proportionately enormous at birth, creating problems at delivery for narrow-hipped, upright-standing women and even more during the first few years, when babies are extremely vulnerable. Factor in the African savannah 2m years ago, teeming with enormous predators, and you wonder how we are still here. For Taylor, the crucial innovation was the baby sling, which enabled proto-human mothers to carry their vulnerable babies (infant apes, of course, cling to their hairy mothers’ backs).