Sexual differentiation in humans Sexual differentiation in humans Sexual differentiation in humans is the process of development of sex differences in humans. It is defined as the development of phenotypic structures consequent to the action of hormones produced following gonadal determination. Sexual differentiation includes development of different genitalia and the internal genital tracts, breasts, body hair, and plays a role in gender identification. The development of sexual differences begins with the XY sex-determination system that is present in humans, and complex mechanisms are responsible for the development of the phenotypic differences between male and female humans from an undifferentiated zygote. Females have two X
Neoteny in humans Australia, said that he agrees that neoteny in humans may have become "accelerated" through "two-way sexual selection" whereby females have been choosing smart males as mates and males have been choosing smart females as mates. Neoteny has been important to human evolution, because it has increased the maturation period and the size of the human brain. Two to three million years ago, there was an "incomplete segmental duplication of [the] ancestral SRGAP2" gene in the ancestors of humans. This new gene, SRGAC2, slowed spine maturation and allowed for more neuronal migration. As a result, the dendrite spines increased in number