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Title Page

Dedication

Preface

CHAPTER 1 - THE ANIMAL WITH THE WEIRDEST SEX LIEE

CHAPTER 2 - THE BATTLE OF THE SEXES

CHAPTER 3 - WHY DON’T MEN BREAST-FEED THEIR BABIES? The Non-Evolution of Male Lactation

CHAPTER 4 - WRONG THE FOR LOVE The Evolution of Recreational Sex

CHAPTER 5 - WHAT ARE WEN GOOD FOR? The Evolution of Men’s Roles

CHAPTER 6 - MAKING MORE BY MAKING LESS The Evolution of Female Menopause

CHAPTER 7 - TRUTH IN ADVERTISING The Evolution of Body Signals

FURTHER READING

INDEX

Copyright Page

To Marie,

My best friend, coparent, lover, and wife

PREFACE

The subject of sex preoccupies us. It’s the source of our most intense pleasures. Often it’s also the cause of misery, much of which arises from built-in conflicts between the evolved roles of women and men.

This book is a speculative account of how human sexuality came to be the way it now is. Most of us don’t realize how unusual human sexual practices are, compared to those of all other living animals. Scientists infer that the sex life of even our recent apelike ancestors was very different from ours today. Some distinctive evolutionary forces must have operated on our ancestors to make us different. What were those forces, and what really is so bizarre about us?

Understanding how our sexuality evolved is fascinating not only in its own right but also in order to understand our other distinctively human features. Those features include our culture, speech, parent-child relations, and mastery of complex tools. While paleontologists usually attribute the evolution of these features to our attainment of large brains and upright posture, I argue that our bizarre sexuality was equally essential for their evolution.

Among the unusual aspects of human sexuality that I discuss are female menopause, the role of men in human societies, having sex in private, often having sex for fun rather than for procreation, and the expansion of women’s breasts even before use in lactation. To the layperson, these features all seem almost too natural to require explanation. On reflection, though, they prove surprisingly difficult to account for. I’ll also discuss the function of men’s penises and the reasons women but not men nurse their babies. The answers to these two questions seem utterly obvious. Within even these questions, though, lurk baffling unsolved problems.

Reading this book will not teach you new positions for enjoying intercourse, nor will it help you reduce the discomfort of menstrual cramps or menopause. It will not abolish the pain of discovering that your spouse is having an affair, neglecting your joint child, or neglecting you in favor of your child. But this book may help you understand why your body feels the way it does, and why your beloved is behaving the way he or she is. Perhaps, too, if you understand why you feel driven to some self-destructive sexual behavior, that understanding may help you to gain distance from your instincts and to deal more intelligently with them.

Earlier versions of material in some chapters appeared as articles in Discover and Natural History magazines. It is a pleasure to acknowledge my debt to many scientist colleagues for discussions and comments, to Roger Short and Nancy Wayne for their scrutiny of the whole manuscript, to Ellen Modecki for the illustrations, and to John Brockman for the invitation to write this book.

CHAPTER 1

THE ANIMAL WITH THE WEIRDEST SEX LIEE

If your dog had your brain and could speak, and if you asked it what it thought of your sex life, you might be surprised by its response. It would be something like this:

Those disgusting humans have sex any day of the month! Barbara proposes sex even when she knows perfectly well that she isn’t fertile—like just after her period. John is eager for sex all the time, without caring whether his efforts could result in a baby or not. But if you want to hear something really gross—Barbara and John kept on having sex while she was pregnant! That’s as bad as all the times when John’s parents come for