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
Archaic humans In this case the standard taxonomy is used, i.e. "Homo rhodesiensis", or "Homo neanderthalensis". The evolutionary dividing lines that separate modern humans from archaic humans and archaic humans from "Homo erectus" are unclear. The earliest known fossils of anatomically modern humans such as the Omo remains from 195,000 years ago, "Homo sapiens idaltu" from 160,000 years ago, and Qafzeh remains from 90,000 years ago are recognizably modern humans. However, these early modern humans do possess a number of archaic traits, such as moderate, but not prominent, brow ridges. The emergence of archaic humans is sometimes used as an example of