<P> Sex differences in humans , or gender differences in humans , have been studied in a variety of fields . In humans , biological sex is determined by five factors present at birth : the presence or absence of a Y chromosome , the type of gonads , the sex hormones , the internal reproductive anatomy ( such as the uterus in females ) , and the external genitalia . Genetic sex is determined solely by the presence or absence of a Y chromosome . A child 's presumed sex is determined at birth by observation of the external genitalia . </P>
which body system differentiates a male from a female
reproductive