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Through riveting personal stories and the latest research, Harvard evolutionary biologist Carole Hooven shows how testosterone drives the behavior of the sexes apart and how understanding the science behind this hormone is empowering for all.

Since antiquity – from the eunuchs in the royal courts of ancient China to the booming market for “elixirs of youth” in 19th-century Europe – humans have understood that typically masculine behavior depends on testicles, the main source of testosterone in males. Which sex has the highest rates of physical violence, hunger for status, and desire for a high number of sex partners? Just follow the testosterone.

Although we humans can study and reflect on our own behavior, we are also animals, the products of millions of years of evolution. Fascinating research on creatures from chimpanzees to spiny lizards shows how high testosterone helps males out-reproduce their competitors. And men are no exception.