Men, towards the end of the last millennium, felt a sudden tightening of the bowels with the news that the services of their sex had at last been dispensed with. Dolly the Sheep - conceived without male assistance - had arrived. Her birth reminded at least half the population of how precarious man's position may be. What is the point of being a man? For a brief and essential instant he is a donor of DNA; but outside that glorious moment his role is hard to understand.

This book is about science not society; about maleness not manhood. The condition is, in the end, a matter of biology, whatever limits that science may have in explaining the human condition. Today's advances in medicine and in genetics mean at last we understand why men exist and why they are so frequent. We understand from hormones to hydraulics how man's machinery works, why he dies so young and how his brain differs from that of the rest of mankind.