Two fascinating questions lie at the heart of The Red Queen: Why is Homo sapiens a sexual species, and what implications does this have for human nature?

That man is sexual may seem unremarkable, yet in fact not all plants and animals need to have sex to reproduce; simple cloning is practiced by many animals with much greater efficiency. To understand how life evolves, and what benefit sex provides for humans, we must think like the Red Queen in Lewis Carroll's Through the Looking-Glass, who had to keep running just to stay in place.

According to a controversial yet persuasive new theory, evolution is not about progress, but about changing in order to survive. Because humans are in a perpetual battle with the parasites lurking within our bodies, we need to be able to change molecular locks as fast as parasites invent new keys. Sex enables us to alter genetic combinations every generation. Sex, then, is a vital weapon in disease resistance. It enables us to change, not so we progress ahead, but so we avoid falling behind.

But what does all this mean for human nature? From a lucid overview of the Red Queen theory, Matt Ridley follows the logic of its argument into the heart of human behavior. For just as the human eye is a product of evolution, so is human nature.

Evolutionary theory provides the clues to help us understand fundamental facts about human beings, from our fashion consciousness to our "system of monogamy plagued by adultery." Ridley's probing mind asks a series of provocative questions. Is mankind naturally polygamous like most of our ape relatives? Are men and women mentally different as well as physically, and if so why? Why do people share so many sexual habits with swallows? Are our notions of human beauty arbitrary, or is there method in them?

Jumping into the middle of the debate over the definition of "human nature," The Red Queen offers an extraordinary new way of interpreting the human condition and how it has evolved. It throws fresh light on seduction and sexism, beauty and polygamy, attraction and adultery - even intelligence itself. This is a brilliantly written book of considerable intrigue and uncommon sense.