Gender: biological theory

Women and men are chromosomally different. Women have two X chromosomes (XX), whereas men have an X and a Y chromosome (XY). In the period following conception, female and male embryos are indistinguishable apart from their chromosomes. However, the Y chromosome in males starts to promote the production of testosterone and other androgens (male sex hormones). These androgens cause the male to develop testes and a penis instead of ovaries and a uterus. The androgens also cause the male brain to develop differently from the female. A biopsychologist would argue that it is these differences in brain development, and the differences in brain activity caused by the secretion of androgens in adulthood, that cause men to behave differently from women (e.g. acting more aggressively).