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
Muscular evolution in humans but what was gained was the ability to hold a club or throw a spear and use the other free hand for another task. This adaptation also helped humans stand up straight with locked knees for longer periods of time. The plantaris muscle in the foot which helped our ancestors grab and manipulate objects like chimps do, has adapted to its new evolutionary role appropriately, becoming so underdeveloped that it cannot grip or grab anything, the foot has grown more elongated as a result and now 9% of humans are born without it. Homo sapiens benefitted by becoming a better