Table Of ContentWHY SEX MATTERS
2
REVISED EDITION
WHY SEX MATTERS
a darwinian look at human behavior
BOBBI S. LOW
PRINCETON UNIVERSITY PRESS
PRINCETON AND OXFORD
3
Copyright © 2015 by Princeton University Press
Published by Princeton University Press, 41 William Street,
Princeton, New Jersey 08540
In the United Kingdom: Princeton University Press, 6 Oxford Street, Woodstock, Oxfordshire OX20 1TW
press.princeton.edu
Jacket image © Jezper/Shutterstock.
Jacket design by Lorraine Betz Doneker.
All Rights Reserved
Library of Congress Cataloging-in-Publication Data
Low, Bobbi S.
Why sex matters : a darwinian look at human behavior / Bobbi S. Low. —Revised edition
pages cm
Summary: “Why are men, like other primate males, usually the aggressors and risk takers? Why do women
typically have fewer sexual partners? In Why Sex Matters, Bobbi Low ranges from ancient Rome to modern
America, from the Amazon to the Arctic, and from single-celled organisms to international politics, to show that
these and many other questions about human behavior largely come down to evolution and sex. More precisely,
as she shows in this uniquely comprehensive and accessible survey of behavioral and evolutionary ecology, they
come down to the basic principle that all organisms evolved to maximize their reproductive success and seek
resources to do so, but that sometimes cooperation and collaboration are the most effective ways to succeed.
This newly revised edition has been thoroughly updated to include the latest research and reflect exciting
changes in the field, including how our evolutionary past continues to affect our ecological present”—Provided
by publisher.
Includes bibliographical references and index.
ISBN 978-0-691-16388-8 (paperback)
1. Human evolution. 2. Sex role. 3. Nature and nurture. 4. Sociobiology. I. Title.
GN281.4.L68 2015
304.5—dc23 2014027259
British Library Cataloging-in-Publication Data is available
This book has been composed in Minion Pro and Helvetica Neue Printed on acid-free paper. ∞
Printed in the United States of America
10 9 8 7 6 5 4 3 2 1
4
FOR MY SON, MICHAEL,
and his family, and for my growing academic lineage, many of whom work
in the “real” world, tackling the problems I raise in chapter 15.
I now have grandchildren in both lineages and am grateful to all
generations, up and down.
May the lineages increase!
5
Contents
Preface xi
1INTRODUCTION 1
Vampire Stories and Beyond 2
Explaining Behavior without Folklore 4
Kinds of “Why” Questions 6
Simple Rules, Complex Outcomes 8
Humans as Critters 8
2RACING THE RED QUEEN: SELFISH GENES AND THEIR STRATEGIES 14
Whose Genes Count, and Why? Kin Selection 17
Summing Up the Basics: Assumptions and Objections 21
Novel Evolutionary Environments: Can the Principles Still Hold? 24
More than Ants or Peacocks: Lifetimes, Culture, Ecology, and Variation 26
3THE ECOLOGY OF SEX DIFFERENCES 28
Sex and Strategies 30
The Ecology of Being Male and Female 35
Mating Effort 38
Parental Effort 42
Variance in Reproductive Success: Mating versus Parental Strategists 43
4SEX, STATUS, AND REPRODUCTION AMONG THE APES 47
The Ecology of Dominance and Reproductive Success in Primates 48
Ecological Aspects of Mating Systems 50
Sex, Resources, and the Ecology of Human Reproduction 51
The Ecology of Human Mating Systems 59
The Ecology of Monogamy and Polyandry 66
5SEX, RESOURCES, APPEARANCE, AND MATE CHOICE 69
Beauty, Resources, and Mate Choice 70
What Men and Women Want 71
Influences on Mate Choice in Modern Western Societies 75
Signals of Desirability and Their Manipulation 77
Who Can Choose? 80
6SEX, RESOURCES, AND HUMAN LIFETIMES 82
Starting Out: Resource Striving in the Womb 85
6
Sex Differences in Development 86
What’s a Mother to Do? Optimizing Maternal Effort among Offspring 87
Conflicts of Interest: Abortion, Infanticide, Abandonment, Neglect 88
Sex Differences in Reproductive Lifetimes 92
Sex Differences in Senescence 99
7SEX AND RESOURCE ECOLOGY IN TRADITIONAL CULTURES 104
Sexual Divisions of Labor 104
Sex and Control of Resources 106
Men, Women, and Resources in Traditional and Historical Cultures 106
8SEX, RESOURCES, AND FERTILITY IN TRANSITION 116
Germany in the Eighteenth and Nineteenth Centuries 117
Nineteenth-Century Sweden 118
Sex, Resources, and Fertility in Transition 132
Fertility Transitions: What, If Anything, Do They Mean? 133
9NICE GUYS CAN WIN—IN SOCIAL SPECIES, ANYWAY 135
Are We Lemmings? A Cautionary Tale 135
When and Why Do We Cooperate Most Easily? 136
Simple Strategies for Winning Games 138
Reciprocity and Its Relatives 141
Adding a Little Complexity 142
The “Group Selection” Naming Muddle 143
Altruists or Good Neighbors? 150
Cooperation and Free Riders 151
10CONFLICTS, CULTURE, AND NATURAL SELECTION 152
Cooperation, Competition, and Groups 153
Working Out Our Conflicts: Moral Systems and Group Life 153
I’m Committed, Are You? The Deception and Manipulation Problems 157
Intertwining Cultural and Natural Selection 157
Logically Inept, Socially Adept: The Social Contexts of Intelligence 165
11SEX AND COMPLEX COALITIONS 170
Coalitions, Resources, and Reproduction 172
Coalitions and the Ecology of Trust 180
Sex and Human Coalitions 181
12POLITICS AND REPRODUCTIVE COMPETITION 185
Men, Women, and Politics Cross-Culturally 187
Women in Politics: When Did It Pay? 195
13SEX, RESOURCES, AND EARLY WARFARE 198
Resources and Conflict 199
Why Women Warriors Are Rare 201
War: Runaway Sexual Selection? 202
7
Other Biological Approaches to Understanding War 203
The Ecology of War: Uncertainty and Payoffs 204
Intergroup Conflict in Other Species 205
Conflict in Preindustrial Societies 208
14SOCIETAL COMPLEXITY AND THE ECOLOGY OF WAR 212
Greek Hoplites: Early “Western” Warriors? 215
The Ecology of Renaissance War 215
The Behavioral Ecology of Modern War 217
Women and Disadvantaged Men in War 220
War and Reproductive Success Today 221
Proximate and Ultimate Causes of War: Evolutionary Novelty 222
15WEALTH, FERTILITY, AND THE ENVIRONMENT IN FUTURE TENSE 225
Wealth, Fertility, and Consumption Today: Empirical Data 231
How Our Evolved Tendencies Affect Our Future 237
The Behavioral Ecology of Humans and Other Species Interact 240
What’s Missing in Current Strategies? 244
Can New Strategies and Tactics Help? 248
An Evolutionary Bottom Line: Can We Use What We Know? 249
253
Notes
319
Glossary
329
References
399
Index
8
Preface
WHEN I WROTE the first version of Why Sex Matters, I suggested that sex differences
are central to our lives, wherever and whenever—however—we live. They still are.
And no matter our age or stage, we still think about them. Sex differences present us
with a fascinating tangle: What do the widely acclaimed (and equally widely
denied) differences between men and women mean in terms of the ways in which
men and women use resources, take risks, make war, and raise children? Which
differences are lasting, which are ephemeral? If we follow the differences through
time, across space, and into different environments, what do they mean in today’s
societies?
Fourteen years ago was an exciting time to study sex differences, but it is even
more exciting now. The general recognition was that, although environmental
conditions can exaggerate or minimize differences in male and female behaviors,
under most conditions each sex has been successful as a result of very different
behaviors. The results are more complex—and more interesting—than we knew. We
humans must solve the same ecological problems as all other species. In biological
terms the currencies are, in the end, reproductive; that is, who survives and who
reproduces best? This principle seems so simple that it is hard to imagine that
diverse and complicated behaviors could arise from it. Yet behaviors vary greatly,
because the ecological (including social) conditions that shape our lives’ success
vary so widely.
There are three themes in this work, as in the first edition. First, resources are
useful in human survival and reproduction; like other living things, we have evolved
to wrest resources from the environment for our benefit, and today we know much
more about how this operates. Second, the two sexes tend to differ in how they can
use resources most effectively to accomplish survival and reproduction. Third, how
each sex accomplishes these ends relies not only (and not obviously) on differences
in genes but also on differences in environment—there are no identified genes
specific for polygyny, for example, but in many environments the trends for male
mammals to profit from trying to be polygynous are strong.
These intertwined themes of resource utility, sex differences, and environmental
constraints soon lead us to consider other problems: for example, status striving and
risk taking. They help us understand why homicide is largely a male endeavor, and
why men and women are jealous about different things. What happens to
populations is the aggregate of what men and women do as they grow, mate, raise
children, and endow those children as well as they can. What can we do about the
9
fact that many of today’s problems have relatively straightforward technical
solutions but that many of our strategies to get both men and women to “do the
right thing” are ineffective? Is prosociality—the tendency to be social—enough?
So much has been explored, and today we understand more deeply some issues
that were new and explained too simply at first. Peter Richerson, Rob Boyd, Richard
McElreath and others have deepened our understanding of cultural evolution; Ernst
Fehr and colleagues have extended our understanding of fairness; Joseph Henrich
and colleagues have demonstrated how variable such concepts can be cross-
culturally. Anthropologists such as Michael Gurven have taken analyses of a
traditional society to depths not previously reached (and more) by anyone except
perhaps Kim Hill and Magdalena Hurtado, spurred in part by the pioneering work of
Napoleon Chagnon and Bill Irons.
I have not changed the structure of the book greatly, but much information is
new, and in chapter 15 I try to link our evolutionary past with our ecological future.
I will begin with the basic arguments and assumptions of behavioral and
evolutionary ecology: selfish genes, conflicts of interest, and why two (and not more
or fewer) sexes have specialized to reproduce through different behaviors (chapters
1–3). Then I ask, how do these basic sex differences, whose theory we understand,
actually play out in primates, including humans (chapters 4–6)? Next, I take an
empirical glance at the diverse ways in which both traditional and transitional
societies make a living, how men’s and women’s roles and lives diverge, and how
even marriage is affected by ecology and resources (chapters 7, 8). The complexity
of these patterns leads us back to basic theory, to explore how conflicts of interest
are mediated, literally from the level of genes in genomes to whole societies
(chapters 9, 10). Sex differences and conflicts of interest help us predict why there
are so few women warriors or high-roller politicians in many societies—and the
kinds of societies in which they are likely to occur (chapters 11–14). Finally, I ask,
How does our heritage from our evolutionary past interact with current global
population and resource-consumption problems (chapter 15)? Does sex still matter?
Have we, in creating novel environments, changed the rules so that now it may even
be detrimental to “strive” to our utmost abilities? Have we gotten ourselves into a
bind in which the behaviors we have evolved to do, and do ever more efficiently,
are now the behaviors that threaten our very existence?
I draw cross-cultural examples from traditional, historical, and modern societies
and from physical, physiological, demographic, and behavioral data (very
occasionally, a little genetics will sneak in). I’ll share my interests and my concerns,
but I cannot offer cut-and-dried solutions. My purpose is to ask, here is a puzzle, a
conundrum—what ideas, old and new, can we use to solve it? I would like to reach
both general readers and scholars in the traditional human disciplines with concepts
that may be new.
Many people helped me greatly. Thanks first to Rob Kurzban, whose kind words
about an interview convinced Princeton that a revised edition, when fields are
moving so fast, might be a good idea.
10
