The origin and meaning of physical and behavioral differences between males and females were thoroughly investigated by Charles Darwin in “The Descent of Man, and Selection in Relation to Sex” (1871). Sexual selection consists of selection based on choices made between males and females, and the intra-sexual selection based on competition between members of the same gender to have a preferencial access to the reproduction. Commonly, sexual selection is amplified if one gender seeks to limit the reproductive success of the other one, due to the major investment in reproduction that a gender shown in comparison to the other, wich is a common behavior in all mammals. It should be also a prerogative of our species that, however, is only moderately dimorphic. The human male is nevertheless on average taller, heavier, stronger, and more brawny than female, but not so different as can be seen in other primates. Psychological and behavioral differences between human males and females are present from birth, following exposure of males to the intrauterine testosterone, and are emphasized with sexual development. In this paper we present some of the most recent acquisitions regarding the role that psychological and behavioral differences between males and females may occur in the criminological context. Also, will introduce some evidence to assert the hypothesis that, in the human species, the physical, psychological and behavioral dimorphism, and therefore the phenomena of differentiation between males and females in aggressive and/or criminal behavior, concerns more sexual selection, and therefore the reproductive fitness, rather than a hypothetical fight for survival.
