Mothers and Others Read online

  MOTHERS AND OTHERS

  Mothers and Others

  * * *

  THE EVOLUTIONARY ORIGINS OF MUTUAL UNDERSTANDING

  Sarah Blaffer Hrdy

  The Belknap Press of Harvard University Press Cambridge, Massachusetts · London, England

  Copyright © 2009 by Sarah Blaffer Hrdy

  ALL RIGHTS RESERVED

  Printed in the United States of America

  First Harvard University Press paperback edition, 2011

  Library of Congress Cataloging-in-Publication Data

  Hrdy, Sarah Blaffer, 1946-

  Mothers and others : the evolutionary origins of mutual understanding / Sarah Blaffer Hrdy.

  p. cm.

  Includes bibliographical references and index.

  ISBN 978-0-674-03299-6 (cloth: alk. paper)

  ISBN 978-0-674-06032-6 (pbk.)

  1. Mother and child. 2. Parental behavior in animals.

  3. Child rearing--Psychological aspects. 4. Behavior evolution.

  I. Title.

  BF723.M55H73 2009

  155.7—dc22

  2008052936

  For my children

  and my children’s children

  CONTENTS

  1 Apes on a Plane

  2 Why Us and Not Them?

  3 Why It Takes a Village

  4 Novel Developments

  5 Will the Real Pleistocene Family Please Step Forward?

  6 Meet the Alloparents

  7 Babies as Sensory Traps

  8 Grandmothers among Others

  9 Childhood and the Descent of Man

  Notes

  References

  Acknowledgments

  Index

  The leading problem in sociobiology today is explaining why we have prosocial emotions.

  —H. Gintis (2001)

  Which is why we need to keep in mind that

  . . . the causal chain of adaptive evolution begins with development.

  —M. J. West-Eberhard (2003)

  1

  APES ON A PLANE

  However selfish . . . man may be supposed, there are evidently some principles in his nature which interest him in the fortunes of others.

  —Adam Smith (1759)

  Each year 1.6 billion passengers fly to destinations around the world. Patiently we line up to be checked and patted down by someone we’ve never seen before. We file on board an aluminum cylinder and cram our bodies into narrow seats, elbow to elbow, accommodating one another for as long as the flight takes.

  With nods and resigned smiles, passengers make eye contact and then yield to latecomers pushing past. When a young man wearing a backpack hits me with it as he reaches up to cram his excess paraphernalia into an overhead compartment, instead of grimacing or baring my teeth, I smile (weakly), disguising my irritation. Most people on board ignore the crying baby, or pretend to. A few of us are even inclined to signal the mother with a sideways nod and a wry smile that says, “I know how you must feel.” We want her to know that we understand, and that the disturbance she thinks her baby is causing is not nearly as annoying as she imagines, even though we also can intuit, and so can she, that the young man beside her, who avoids looking at her and keeps his eyes determinedly glued to the screen of his laptop, does indeed mind every bit as much as she fears.

  Thus does every frequent flier employ on a regular basis peculiarly empathic aptitudes for theorizing about the mental states and intentions of other people, our species’ gift for mutual understanding. Cognitively oriented psychologists refer to the ability to think about what someone else knows as having a “theory of mind.”1 They design clever experiments to determine at what age human children acquire this ability and to learn how good at mind reading (or more precisely, attributing mental states to others) nonhuman animals are. Other psychologists prefer the related term “intersubjectivity,” which emphasizes the capacity and eagerness to share in the emotional states and experiences of other individuals—and which, in humans at least, emerges at a very early stage of development, providing the foundation for more sophisticated mind reading later on.2

  Whatever we call it, this heightened interest in and ability to scan faces, and our perpetual quest to understand what others are thinking and intending, to empathize and care about their experiences and goals, help make humans much more adept at cooperating with the people around us than other apes are. Far oftener than any of us are aware, humans intuit the mental experiences of other people, and—the really interesting thing—care about having other people share theirs. Imagine two seat-mates on this plane, one of whom develops a severe migraine in the course of the flight. Even though they don’t speak the same language, her new companion helps her, perhaps holding a wet cloth to her head, while the sick woman tries to reassure her that she is feeling better. Humans are often eager to understand others, to be understood, and to cooperate. Passengers crowded together on an aircraft are just one example of how empathy and intersubjectivity are routinely brought to play in human interactions. It happens so often that we take the resulting accommodations for granted. But just imagine if, instead of humans being crammed and annoyed aboard this airplane, it were some other species of ape.

  At moments like this, it is probably just as well that mind reading in humans remains an imperfect art, given the oddity of my sociobiological musings. I cannot keep from wondering what would happen if my fellow human passengers suddenly morphed into another species of ape. What if I were traveling with a planeload of chimpanzees? Any one of us would be lucky to disembark with all ten fingers and toes still attached, with the baby still breathing and unmaimed. Bloody earlobes and other appendages would litter the aisles. Compressing so many highly impulsive strangers into a tight space would be a recipe for mayhem.

  Once acquired, the habit of comparing humans with other primates is hard to shake. My mind flits back to one of the earliest accounts of the behavior of Hanuman langurs, a type of Asian monkey that, as a young woman, I went to India to study. T. H. Hughes was a British functionary and amateur naturalist who had been sent out to the subcontinent to help govern the Raj. “In April 1882, when encamped at the village of Singpur in the Sohagpur district of Rewa state . . . My attention was attracted to a restless gathering of ‘Hanumans,’” wrote Hughes. As he watched, a fight broke out between two males, one of them traveling with a group of females, the other presumably a stranger. “I saw their arms and teeth going viciously, and then the throat of one of the aggressors was ripped right open and he lay dying.” At that point Hughes surmised that “the tide of victory would have been in [the stranger’s favor] had the odds against him not been reinforced by the advance of two females . . . Each flung herself upon him, and though he fought his enemies gallantly, one of the females succeeded in seizing him in the most sacred portion of his person, depriving him of his most essential appendages.”3

  Descriptions of missing digits, ripped ears, and the occasional castration are scattered throughout the field accounts of langur and red colobus monkeys, of Madagascar lemurs, and of our own close relatives among the Great Apes. Even among famously peaceful bonobos, a type of chimpanzee so rare and difficult to access in the wild that most observations come from zoos, veterinarians sometimes have to be called in following altercations to stitch back on a scrotum or penis. This is not to say that humans don’t display similar propensities toward jealousy, indignation, rage, xenophobia, or homicidal violence. But compared with our nearest ape relations, humans are more adept at forestalling outright mayhem. Our first impulse is usually to get along. We do not automatically attack a stranger, and face-to-face killings are a much harder sell for humans than for chimpanzees. With 1.6 billion airline passengers annually compressed and manhandled,
no dismemberments have been reported yet. The goal of this book will be to explain the early origins of the mutual understanding, giving impulses, mind reading, and other hypersocial tendencies that make this possible.

  “WIRED” TO COOPERATE

  From a tender age and without special training, modern humans identify with the plights of others and, without being asked, volunteer to help and share, even with strangers. In these respects, our line of apes is in a class by itself. Think back to the tsunami in Indonesia or to hurricane Katrina. Confronted with images of the victims, donor after donor offered the same reason for giving: Helping was the only thing that made them feel better. People had a gut-level response to seeing anguished faces and hearing moaning recitals of survivors who had lost family members—wrenching cues broadcast around the world. This ability to identify with others and vicariously experience their suffering is not simply learned: It is part of us. Neuroscientists using brain scans to monitor neural activity in people asked to watch someone else do something like eating an apple, or asked just to imagine someone else eating an apple, find that the areas of the brain responsible for distinguishing ourselves from others are activated, as are areas of the brain actually responsible for controlling the muscles relevant to apple-eating. Tests in which people are requested to imagine others in an emotional situation produce similar results.4 It is a quirk of mind that serves humans well in all sorts of social circumstances, not just acts of compassion but also hospitality, gift-giving, and good manners—norms that no culture is without.

  Reflexively altruistic impulses are consistent with findings by neuroscientists who use magnetic resonance imaging (MRI) to monitor brain activity among experimentally paired strangers engaged in a variant of a famous game known as the Prisoner’s Dilemma. In this situation, two players earn rewards either by cooperating or defecting. If neither player defects and both continue to cooperate over sequential games, both gain more than they would have without playing at all. But if one player opts out while his partner cooperates, the defector wins even more and his partner gets nothing. If both defect, they lose out entirely. Such experiments yield a remarkable result. Even when players are told by the experimenters that this is going to be a one-shot game, so that each player has only one chance to cooperate or defect, with no possibility of cooperating again to mutual advantage, 42 percent of randomly selected strangers nevertheless opt to behave cooperatively.5

  Compassion is not necessarily confined to group members. The Spanish soldier shown here is using his own body’s warmth to revive an African refugee who was rescued while attempting to cross by boat from Morocco to Spain. (R. Perales/AP)

  Such generosity at first seems irrational, especially to economists who are accustomed to celebrating individualism and economic models that assume self-interested “rational actors,” or to a sociobiologist like me who has devoted much of her professional life researching competition between primate males for access to fertile females, between females in the same group for resources, and even between offspring in the same family for access to nourishment and care. When considered in the context of how humankind managed to survive vast stretches of time and dramatic fluctuations in climate during the Pleistocene, in the period from around 1.8 million years ago until about 12,000 BCE, such generous tendencies turn out to be “better than rational” because people had to rely so much on time-tested relationships with others.6

  Among people living in small, widely dispersed bands of interconnected families likely to interact again and again, prosocial impulses—meaning tendencies to voluntarily do things that benefit others—are likely to be reciprocated or rewarded. The generous person’s well-being and that of his or her family depended more on maintaining the web of social relationships that sustained them through good times and bad than on the immediate outcome of a particular transaction. The people you treat generously this year, with the loan of a tool or gift of food, are the same people you depend on next year when your waterholes dry up or game in your home range disappears.7 Over their lifetimes people would encounter and re-encounter their neighbors, not necessarily often, but again and again. Failures to reciprocate would result in loss of allies or, worse still, social exclusion.8

  Jump ahead thousands of years to the laboratories where researchers administer such experiments today. As shown by research subjects who cooperate even when there is no possibility for the favor to be reciprocated, “one-shot deals” are not an eventuality that human brains were designed to register. Right from an early age, even before they can talk, people find that helping others is inherently rewarding, and they learn to be sensitive to who is helpful and who is not.9 Regions of the brain activated by helping are the same as those activated when people process other pleasurable rewards.10

  Anyone who assumes that babies are just little egotists who enter the world needing to be socialized so they can learn to care about others and become good citizens is overlooking other propensities every bit as species-typical. Humans are born predisposed to care how they relate to others. A growing body of research is persuading neuroscientists that Baruch Spinoza’s seventeenth-century proposal better captures the full range of tensions humans grow up with. “The endeavor to live in a shared, peaceful agreement with others is an extension of the endeavor to preserve oneself.” Emerging evidence is drawing psychologists and economists alike to conclude that “our brains are wired to cooperate with others” as well as to reward or punish others for mutual cooperation.11

  Perhaps not surprisingly, helpful urges are activated most readily when people deal with each other face-to-face. Specialized regions of the human brain, huge areas of the frontal and parietotemporal cortex, are given over to interpreting other people’s vocalizations and facial expressions. Right from the first days of life, every healthy human being is avidly monitoring those nearby, learning to recognize, interpret, and even imitate their expressions. An innate capacity for empathizing with others becomes apparent within the first six months.12 By early adulthood most of us will have become experts at reading other people’s intentions. So attuned are we to the inner thoughts and feelings of those around us that even professionals trained not to respond emotionally to the distress of others find it difficult not to be moved. Therapists face particular challenges in this respect. Empathy, the stock-in-trade of psychotherapists because it really does produce better results, turns out to be their worst nightmare as well.13 People who deal day-in-and-day-out with the troubles of others face such occupational hazards as “vicarious traumatization” and “compassion fatigue,” or face the threat of “catching” a client’s depression.14

  New discoveries by evolutionarily minded psychologists, economists, and neuroscientists are propelling the cooperative side of human nature to center stage. New findings about how irrational, how emotional, how caring, and even how selfless human decisions can be are transforming disciplines long grounded in the premise that the world is a competitive place where to be a rational actor means being a selfish one. Researchers from diverse fields are converging on the realization that while humans can indeed be very selfish, in terms of empathic responses to others and our eagerness to help and share with them, humans are also quite unusual, notably different from other apes.15

  “Without prosocial emotions,” two theoretical economists opined recently, “we would all be sociopaths, and human society would not exist, however strong the institutions of contract, governmental law enforcement and reputation.”16 Coming from practitioners of the dismal science, this is revolutionary stuff. For evolutionists, it requires either special pleading or else new ways of thinking about how our species evolved and what being human means.

  WHAT IT MEANS TO BE EMOTIONALLY MODERN

  Time and again, anthropologists have drawn lines in the sand dividing humans from other animals, only to see new discoveries blur the boundaries. We drew up these lists of uniquely human attributes without realizing how much more they revealed about our ignorance of other animals than about t
he special attributes of our species. By the middle of the twentieth century, Man the Toolmaker had lost pride of place as Japanese and British researchers watched wild chimpanzees tailor twigs to fish for termites.17 By now, every one of the Great Apes is known to select, prepare, and use tools, crafting natural objects into sponges, umbrellas, nutcrackers—even sharpening sticks for jabbing prey.18 Furthermore, Great Apes have unquestionably been using tools for a long time. Archaeologists trace the special stone mortars that chimpanzees in west Africa use for nut cracking back in time at least 4,300 years.19

  Great Apes employ tools in a wide range of contexts, and do so spontaneously, inventively, and sometimes with apparent foresight. In a recent article in Science magazine titled “Apes Save Tools for Future Use,” Nicholas Mulcahy and Josep Call describe orangutan and bonobo subjects who were trained to use particular tools to solve a problem and earn a reward, and then were permitted to select particular tools to bring with them for tasks they would be asked to perform an hour later. They chose the tools likely to be most useful. Such experiments have led primatologists (and even comparative psychologists working with smart birds like corvids) to credit nonhuman animals with some ability to plan ahead.20

  Arguably, Great Apes have been making and using tools since they last shared common ancestors with humans and with each other, and they transmitted this technological expertise along with various behaviors (like grooming protocol or greeting ceremonies) from one generation to another so that different populations have different repertories. Other apes also store memories much as we do, and in terms of spatial cognition or traits such as their ability to remember ordered symbols that briefly flash up on a computer screen, specially trained chimpanzees test better than graduate students.21 In general, the basic cognitive machinery for dealing with their physical worlds is remarkably similar in humans and other apes.22