“Among Norway rats, males ejaculate more sperm when copulating in the presence of male rivals, seemingly because the competition to reproduce persists all the way up the fallopian tube to the surface of the egg. For the same reason, an ape’s testicles are proportionate to the size of the male breeding pool. The male chimpanzee, surrounded by ruthless competition, has reproductive equipment that is truly prodigious, while the gorilla, living with a harem as the only male, has nothing to brag about. The evolutionary reason: A male without rivals needs no special adaptations to increase his odds of becoming a father. Once again, the social and the physiological cannot be separated any more than we can separate the length from the width of a rectangle.” Human NatureLonelinessGenetical Book:Loneliness: Human Nature and the Need for Social Connection Source: Loneliness: Human Nature and the Need for Social Connection