We inherit mechanisms for survival from our primeval past; none so obviously as those involved in reproduction. The hormone testosterone underlies the organization of activation of masculinity: it changes the body and brain to make a male. It is involved not only in sexuality but in driving aggression, competitiveness, risk-taking - all elements that were needed for successful survival and reproduction in the past. But these ancient systems are carried forward into a modern world. The ancient world shaped the human brain, but the modern world is shaped by that brain. How does this world, with...