In his highly entertaining and enlightening book, the acclaimed geneticist and author Steve Jones offers a landmark exploration of maleness. With effervescent wit, Jones argues that men, biologically speaking, are the true second sex. Here he lays out the cases for and against masculinity -- exploring every biological aspect from the genesis of the Y chromosome onward -- based on the recent explosion of biological research. Along the way, he offers pithy commentary on topics such as male hormones, hair loss, and the hydraulics of man's most intimate organ. Fascinating and often surprising, Jones's evidence offers fresh fuel for the battle of the sexes.