http://ndnd.essortment.com/sexualdimorphis_rcgt.htm

Sexual dimorphism manifests itself in humans by differences in overall body size traits, compared to the larger degree of sexual dimorphism displayed by other primates, especially chimpanzees and bonobos. Less sexual dimorphism often indicates a species with mutual care of the young and monogamy, such as birds, whereas greater sexual dimorphism is often demonstrated by species which practice polygamy and have sharply defined gender roles regarding the rearing of offspring