Cordelia Fine’s “Testosterone Rex” is a book about the role testosterone plays in gender development. It’s an interesting investigation of how the mythology surrounding huge differences between the sexes greatly contributes to inequality but has little basis in science. She argues that testosterone, while undoubtedly an important hormone in sexual development, does not play an equally important part in brain development. To show this she includes numerous studies on promiscuity, risk-taking and competitiveness, which reveal surprising similarities between men and women. Fine’s view is that both sexes are made, not born; therefore, the inequality of the sexes is cultural, not natural. She attributes the main role in gender construction to social pressures and cultural norms, not hormones. Thus, she highlights that gender is much more flexible and fluid than is usually assumed.