Human evolution theory utilizing concepts of neoteny & female sexual selection
An etiology of neuropsychological disorders such as autism and dyslexia, and the origin of left handedness.
"Different prehuman species suggest different levels of sperm competition. Judging from its teeth, Australopithecus africanus was certainly a vegetarian. Like gorillas, the vegetarian australopithecines showed a bigger difference in body size between sexes than men and women do today, suggesting that they were sperm-competition avoiders. Although no one, of course, knows for sure, Robert Smith speculates that physically imposing males bossed relatively sexually faithful females in australopithecine harems. These ancestors would have been very sexist, but the males, violently intolerant of promiscuity, would not have developed large genitals. This sultanlike breeding behavior could well have undergone radical change with the evolution of Homo habilis, "handy man": Smith postulates that subordinate habilis males, scavenging meat and offering pieces of it in exchange for sex, upset the earlier breeding system. The cooperative hunting groups that began with Homo erectus --- our most recent evolutionary predecessor --- ushered in relatively high levels of sperm competition. Homo erectus males were not much larger than Homo erectus females. Homo erectus was a communal species who not only gathered edible plants but hunted mammoths and used fire. Eating and sleeping together in groups --- the sort of cooperative groups needed to hunt --- may have made them far more social, more talkative, and better barterers than their sexually dimorphic australopithecine ancestors. And more promiscuous. It was with Homo erectus, Smith suggests, that people developed their relatively large male genitals." (Margulis, L & Sagan, D. (1991) Mystery Dance, On the Evolution of Human Sexuality: Summit Books, New York pp. 51)