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 defender and hunter. An increase in running as a hunting and survival activity was perhaps fundamental to this development While there is no proof that modern humans have become physically weaker than past generations of humans, inferences from such things as bone robusticity and long bone cortical thickness can be made as a representation of physical strength. Taking such factors into account, there has been a rapid decrease in overall robusticity in those populations that take to sedentism. For instance, bone shaft thickness since the 17th and 18th centuries have decreased in the United States, indicating a less physically stressful