The answer that emerges is that men’s testicles are not large enough for a system of promiscuity like the chimpanzee’s, men’s bodies are not big enough for a system of harem polygamy like the gorilla’s (there is an iron link between harem polygamy in a species and a large size differential between male and female), and men are not as antisocial and adjusted to fidelity as the monogamous gibbon. We are somewhere in between.
