T he evolution of nurturant parental behavior constituted a turning point in the evolution of terrestrial vertebrate behavior. Reptilian social behavior is based on repressive dominance and submission, and even their "courtship" behavior is derived from intimidation display, with females assuming submissive postures to express their readiness to copulate.
With the evolution of nurturant parental care, caretaking, corresponding motivations, and individualized bonding came into the world, along with the reciprocal motivation in offspring to seek care and protection and to send signals to trigger nurturant responses. This, of course came hand-in-hand with the capacity of parents to recognize their offspring and vice versa. For animals of the precocial type, this sometimes involves an imprinting-like learning process restricted to a short period after birth or hatching.
Thus, the reptilian heritage was overlaid by new structures in the brain responsible for prosocial behaviors. However, the older structures did not disappear, and in humans they constitute a structure as large as a fist in the brain stem that is still, among many other functions, related to aggression ( Bailey 1987; Eibl- Eibesfeldt 1989, 1990). As a result, even human sexual behavior has dominance and submission components. The remaining link between male sexuality and repressive dominance is demonstrated by the fact that the achievement of dominance, e.g. winning a tennis match, is accompanied by a rise of blood testosterone levels in the winner and a corresponding drop in the loser ( Mazur and Lamb 1980).