Referring to Lewis Carroll's from , a character who has to keep running to stay in the same place, Matt Ridley demonstrates why sex is humanity's best strategy for outwitting its constantly mutating internal predators. answers dozens of other riddles of human nature and culture—including why men propose marriage, the method behind our maddening notions of beauty, and the disquieting fact that a woman is more likely to conceive a child by an adulterous lover than by her husband. offers an extraordinary new way of interpreting the human condition and how it has evolved.