Aggression and Procreation

Aggressive behavior in nearly all species is rooted in sexuality. The male is
usually more aggressive than the female. The sexual act is fundamentally an
act of male aggression. Males during their sexual prime maintain the high
levels of testosterone that assure the continuance of their species but that
also result in aggressive, sometimes antisocial behavior.
The offensive aggression of one species, such as the predatory birds that
feed on newborn turtles in the Galápagos Islands, evokes defensive aggressive
behavior on the part of those seeking to protect their young and to
assure the continuance of their species. The species that demonstrates defensive
aggression in a situation of this sort may demonstrate offensive aggression in pursuing and attacking a weaker species. All of these aggressions
among nonhumans are, in the final analysis, directed at preserving the species.