<Tr> <Td> <Ul> <Li> </Li> <Li> </Li> <Li> </Li> </Ul> </Td> </Tr> <Ul> <Li> </Li> <Li> </Li> <Li> </Li> </Ul> <P> Sex 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), 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> <P> Sex differences generally refer to traits that are sexually dimorphic . A subset of such differences is hypothesized to be a product of the evolutionary process of sexual selection . </P>

What is the main difference between male and female
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