Why Sex Matters

A Darwinian Look at Human Behavior - Revised Edition

Bobbi S. Low

• Publisher: Princeton University Press
• Year: 2015
• ISBN:
  9781400852352
• Topic: Biological Sciences
• Subtopic: Evolution
• Index: Biological Sciences

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.

1

Introduction

Probably a crab would be filled with a sense of personal outrage if it could hear us class it without ado or apology as a crustacean, and thus dispose of it. “I am no such thing,” it would say: “I am MYSELF, MYSELF alone.”

—William James Varieties of Religious Experience (1902)

To the same natural effects we must, as far as possible, assign the same causes.

—Newton

“WHY CAN’T A WOMAN be more like a man?” wailed Professor Henry Higgins in My Fair Lady, the musical derived from George Bernard Shaw’s Pygmalion. Certainly in many societies, across time, there have been women who were “more like a man.” Think of Joan of Arc, who was burned at the stake (on the minor charge of wearing men’s clothing); or of George Sand, of whom Elizabeth Browning said, “You are such a large-brained woman and a large-hearted man.” Yet in part, we remember such women because they are singular, whether we envy their ability to break free or whether we imagine that they missed a lot. What really contributes to the patterns we see—and to their exceptions?

Here I want to explore sex differences from a relatively unusual perspective, one that is often misunderstood. Understanding and explaining human behavior is a central concern for all of us. But doing so—especially when sex differences are the issue—presents a real dilemma. We are complicated, highly social beings. We live in a staggering array of environments, both ecological and social. Our families, lovers, and friends are not exemplars or prototypes, but unique, particular individuals. None of us wants to be “reduced” to some formula.

For, like William James’s crab, we know we are above crude analysis. Even the name we give ourselves, Homo sapiens, reflects both the value that we give to understanding and the fact that we feel ourselves to be special. Like that crab, many people may be appalled at the approach I will use here, that is, to assume that, once we understand environmental and social pressures, we humans are as predictable as other animals in our behavior and are governed by the same rules. And I want to begin with simple rules, no less.

Many of us assume that humans operate under rules that are different from these other species, that our rules are based entirely on culture rather than on biology, or some combination. I will ask: what can we learn if we begin without assuming that this were true? I want to begin by exploring what a biologist would predict if he or she knew only that here was a smart, upright-walking, highly social primate and nothing more. I will explore the ecology of being male and female, beginning with simple rules and with what I can discern about the environments with which the evolutionary rules interact.

The approach I use, behavioral ecology, is an evolutionary approach with roots in Charles Darwin’s work. It focuses on the question, how do environmental conditions influence our behavior and our lifetimes? This approach has proved profitable in exploring other realms of human behaviors.¹ Behavioral ecology and its intellectual relatives seek to understand how comparatively simple operating rules interact with historical accidents, and with temporal and spatial specifics, to yield a rich diversity of patterns. There is no doubt that genes influence not only our physical structure and physiology but also our behavior; there is no doubt that historical accident often plays a role, nor is there any doubt that cultural and social pressures can influence behavior. But where lies the balance? Perhaps by beginning with very simple rules and assumptions, and finding where they fail to predict well, we can gain some insight.²

VAMPIRE STORIES AND BEYOND

Humans have always sought to explain the patterns they see. In fact, one of the strongest selective forces on human behavior has been to understand pattern—not only in order to deal with environmental variation but also to be the first in one’s tribe who is able to predict events and when they will occur (imagine being the first human to predict a solar eclipse). But creating stories that more or less match our observations is not science but folklore.

Consider vampires. From Bram Stoker through Anne Rice, from Bela Lugosi to Tom Cruise and Leslie Nielson, vampires have always fascinated us: aristocratic, sexy, dangerous, and (almost) invincible. Vampire folklore provides a wonderful example of how our need to explain can drive us to spin stories that seem to explain something that we see, and that can be hard to refute, but that nonetheless do not reflect what actually happens.

The folklorist Paul Barber, in a delightful examination of vampire myths around the world, notes that the ways people in preindustrial societies interpreted phenomena associated with death and the decay of corpses are “from our perspective, quite wrong. What makes them interesting, however, is that they are also usually coherent, cover all the data, and provide the rationale for some common practices that seem, at first, to be inexplicable.”³

The variety of myths and legends about vampires all begin simply: death—especially unexpected or unusual death—brings more death. If someone died, “why” was usually unknown, and epidemics leading to death and more death were once far more common than today. Once people were buried (often without coffins), not all corpses had the decency to stay below ground. In a prebacteriology culture, people weren’t likely to see a “flailing” corpse as the natural by-product of bacterial decay, but rather as the will of the dead person or as the rejection of the corpse by Mother Earth. Since death brings death, those first to die, as in an epidemic, were dangerous and somehow had to be disarmed so that they could not continue to bring death. Only when all “changing” ceased, and ashes or bones alone remained, was the corpse neutral, inactive, and no longer dangerous.

People thus began with a repeatable observation: that death brings death. This applies not only to vampires but also to the general idea that dead people call to their relatives and friends and must be propitiated to protect those still alive. Because they had no knowledge of disease transmission, people imbued the corpse with dangerous properties. Not a bad idea, particularly in times of plague, when unexpected deaths were frequent and vampire fears were heightened—but an idea that led to a misinterpretation of the normal signs of decomposition.

In folklore, in a variety of societies around the world, vampires are described as undecomposed; they have a ruddy or dark complexion, do not suffer rigor mortis, are swollen or plump, have blood at the mouth and/or in internal cavities, and grow new skin or nails after burial. In an interesting twist, people suspected of being vampires were frequently buried differently, in ways that made a diagnosis of vampirism more, not less, likely. Suspected vampires were often buried face down, so that if they tried to claw their way out of the earth to torment others, they would dig themselves in deeper. But because blood settles into the lowest capillaries after death, face-down burial meant that the body’s face (rather than the back) would be dark and ruddy. And a ruddy face was believed to be a sign of a vampire. Some putative vampires were buried with lime to hasten their decomposition—but lime in fact retards it. Thus, someone who died in an unusual way and was in danger of becoming a vampire was likely to be buried face down, covered with lime—and thus to have a ruddy face, to decompose more slowly, and, on exhumation, to be confirmed as a vampire. Such practices reinforced mistaken beliefs.

Folklore about vampires arises from an entirely sensible and consistent desire to explain something in the absence of complete information. But what people say about what they see and do can be a rotten path to explanation. Although observers called the corpses undecomposed, they described unmistakable signs of rot (e.g., a stench). Descriptions like “ruddy” or “swollen,” which were used to assert failure to decompose, are in fact signs of the ordinary (but variable) process of decomposition.

It is important to separate carefully what people describe, as they see, hear, and smell what happens, from the causes they attribute. The observation that a corpse stinks is, in fact, consistent with the contention that decay is occurring, but not that it is failing to decompose. It is important to avoid this kind of muddle at all times, not only when we are no longer likely to believe in something like vampirism. Being led astray by “vampire myths” that sound reasonable but are untested is most likely to occur when a behavior is complicated and we want to believe the stories we tell.

EXPLAINING BEHAVIOR WITHOUT FOLKLORE

Other species’ behavior can be more complex than we realize. An excellent example of such complexity generated by the interaction of operating rules (genes), environment, and historical accident is the biologist Bernd Heinrich’s work on food sharing in ravens, Corvus corax. Heinrich saw a curious behavior on a hike in Maine late one October: a group of ravens that were feasting on a dead moose were giving a distinctive, loud, and high-pitched “yell.”⁴ Because other ravens were attracted to the yelling, the result was that there were more competitors at the kill, and thus less food for each of the yellers. Why didn’t the raven who first found the kill just keep quiet? And why weren’t the ravens now fighting over the kill?

If we saw humans share like this, or if we extended our often untested social perceptions about humans to ravens, we would probably think how kind all this indiscriminate sharing is. In fact, that would constitute a vampire story; behavioral ecologists find true genetically costly altruism to be so rare, as I will explain below, as to be a fluke in nonhumans. The ravens who shared seemed to be doing it at a cost. One of Heinrich’s first questions was whether the “called” birds were related to the callers, for sharing with individuals who have at least some genes in common can help copies of one’s own genes. Or were they reciprocators? After much work marking and recapturing ravens in the field, Heinrich was able to eliminate the possibility that ravens were summoning their kin or their reciprocators. Where next?

Heinrich made a series of careful observations, comparing the behavior of different ravens under different circumstances. His summary begins with eleven clues and proceeds from simpler to more complex deductions.⁵ Without giving away the whole plot, I can say that one of his major findings was that adult ravens are territorial, controlling access to any carcasses in their territory and driving off any juveniles found on a carcass. When a juvenile found a carcass, it was likely to “yell,” attracting other juveniles (the largest group at a carcass was about 150). When enough juveniles were present, the resident territorial adults could not drive all of them off. So the cost of additional juvenile competitors could be offset by the benefit of attracting a group large enough to stay on the carcass even if adults were nearby. Clearly the costs and benefits of yelling would vary in different circumstances. Heinrich did not simply create a plausible vampire or just-so story about the juvenile behavior he observed. Instead, he observed, made hypotheses, and tested them to discover the most probable functional reason for the ravens’ behavior.

Heinrich could not know what role any gene plays in this behavior, so he used a technique called the “phenotypic gambit” to make testable predictions: starting from what he saw—the phenotype—he made certain assumptions. He assumed that, whatever the relationship between genes and the set of behaviors he saw, enough time had passed for the system to come to equilibrium and thus what he saw represented the outcome of competing strategies.⁶ The phenotypic gambit is a powerful tool (although sometimes controversial), and I’ll return to it below.

For ravens as for humans, both ecological and social conditions can change the costs and benefits of any action. Heinrich, of course, had to observe the ravens without their cooperation; he had to concentrate on what the ravens actually did. Sociologists, psychologists, and anthropologists find it useful to interview people, and this tells us something about what people themselves imagine they are doing (and, of course, speech itself is a behavior).

Because we can make decisions consciously, often we assume that unless a behavior is consciously considered, it is of no interest. Yet many other species routinely learn and behave in complicated ways without (so far as we can tell, at least) consciousness—or at least without the ability to share abstract sentiment through speech. Furthermore, as I noted above, it is presumptuous to assume that people’s conscious attributions of their behavior are analytically helpful, and if we do assume that, it can cause real trouble.

Behavioral ecologists cannot interview ravens about why they call to other ravens when they find a carcass (who knows what reasons a raven might give, anyway?), and they don’t know the genetics of the situation (is such calling the result of a single gene’s action?). For these reasons, behavioral ecologists concentrate on what happens—on what behaviors show up under what conditions. If we take the same approach in looking at human behavior, we will lose some information about people’s intentions, but we won’t get distracted by our human reports of conscious reasons. And such lack of distraction may prove useful, for what people say is often not consistent with what we observe them doing.⁷

Perhaps new connections will appear as we look past what we imagine behavioral causes to be and as we look beyond what people say about why they act a certain way—if we instead examine carefully what sorts of behaviors we see in particular environments. Without requiring consciousness or rationality (or even speculating on their existence), we can ask what behaviors will be profitable under specific environmental conditions. Then we can ask explicitly how conscious, cultural influences can influence the costs and benefits of these behaviors.

KINDS OF “WHY” QUESTIONS

Heinrich’s analysis of raven behavior highlights an important distinction. To understand “why” we do things, to explain both the behaviors that seem almost universal or unvarying and those that vary greatly, we can seek answers in different ways. “Why” questions have two principal complementary forms in biology: “proximate” and “ultimate” explanations.⁸ Why do birds migrate? One answer might be “changing day length causes hormonal changes, triggering migration.” Both changing day length and changing hormones are proximate triggers, or cues. If we could interview birds, we might have another set of proximate causes, the equivalent of our reasons: “I really hate the cold,” “it makes me feel good,” “that way I get to see my relatives.”

However, proximate answers are no help in explaining why one species migrates while others don’t, why not all individuals in this species migrate (costs and benefits may differ for older, younger, weak, or healthy individuals), or why day length rather than some other cue, or a combination of cues, has become the trigger.

The ultimate cause of migration (and other behaviors) always concerns reproductive success. Seasonal better-versus-worse geographic shifts in foraging and nesting areas mean that individuals who seek the better areas, shifting seasonally, leave more descendants than those who remain in one area. When day length is the ...

Table of contents

• Cover Page
• Title Page
• Copyright Page
• Dedication
• Contents
• Preface
• 1 Introduction
• 2 Racing the Red Queen: Selfish Genes and Their Strategies
• 3 The Ecology of Sex Differences
• 4 Sex, Status, and Reproduction among the Apes
• 5 Sex, Resources, Appearance, and Mate Choice
• 6 Sex, Resources, and Human Lifetimes
• 7 Sex and Resource Ecology in Traditional Cultures
• 8 Sex, Resources, and Fertility in Transition
• 9 Nice Guys Can Win—In Social Species, Anyway
• 10 Conflicts, Culture, and Natural Selection
• 11 Sex and Complex Coalitions
• 12 Politics and Reproductive Competition
• 13 Sex, Resources, and Early Warfare
• 14 Societal Complexity and the Ecology of War
• 15 Wealth, Fertility, and the Environment in Future Tense
• Notes
• Glossary
• References
• Index