Big brains created the obstetric dilemma and extended childhood

Human brains tripled in size relative to our last common ancestor with chimps, and once head size passes roughly the 85th percentile, emergency cesareans and forceps deliveries spike (the 'curse of Eve'); this drove compensating adaptations including self-domestication, neoteny, extended childhood, and a lengthened adolescence that keeps growing as the body of knowledge to be downloaded grows.