Mothers and Others

by Sarah Blaffer Hrdy

  HOW COULD HUMANS BECOME SUCH COOPERATIVE APES?

  The archaeological record over the past 10,000 years, and especially the historical record of the past few millennia, abounds with ruined abodes, smashed skulls, and skeletons penetrated by arrowheads. Beautifully colored murals from ancient Mexico and other locales depict the grisly torture of captured enemies, fearsome and totally convincing war propaganda from the distant past. Such evidence renders a bloody-awful record bloody clear. Yet selfish genes and violent predispositions notwithstanding, it takes high population densities, competition for the same resources, long-standing conflicts of interest, and major provocations (often filtered through virulent ideologies and rabble-rousing propaganda) to persuade human apes that neighboring people are sufficiently alien, evil, and potentially dangerous to warrant face-to-face killing and the risks associated with trying to wipe out another group.73

  One of the most dangerous things that could ever happen to a common chimpanzee would be to find himself suddenly introduced to another group of chimpanzees. A stranger risks immediate attack by the group’s same-sex members. Now think back to Christopher Columbus’s arrival in the Bahamian Islands, his first landfall in the New World. To greet his ship, out came Arawak islanders, swimming and paddling canoes, unarmed and eager to greet the newcomers. Lacking a common language, they proceeded to proffer food and water, as well as gifts of parrots, balls of cotton, and fishing spears made from cane. Something similar may have happened to Captain Cook on his arrival in the Hawaiian islands. “The very instant I leaped ashore,” wrote Cook, the local people “brought me a great many small pigs and gave us without regarding whether they got anything in return.”74

  European sailors were amazed by such spontaneous generosity, although Christopher Columbus simply found the Arawak naive. Columbus’s description of first contact parallels those of Westerners with the Bushmen and other pre-Neolithic peoples: “When you ask for something they have, they never say no. To the contrary, they offer to share with anyone.” But Columbus, himself the product of Europe’s long post-Neolithic traditions, had different ideas: “They do not bear arms, and do not know them, for I showed them a sword . . . and [they] cut themselves out of ignorance,” the explorer noted in his log. “They would make fine servants . . . With fifty men we could subjugate them all and make them do whatever we want.”

  Examples abound of individuals from highly stratified, dominance-oriented, aggressive societies expanding at the expense of people from more egalitarian and group-oriented traditions, people who stockpile social obligations rather than amass things. Alas, it is far easier to imagine the Arawak becoming more like Columbus than the other way around. Only with more reliable food sources from unusually rich coastal or freshwater habitats or with food surpluses from horticulture or herding would higher population densities and increasingly stratified societies become possible, along with the need to protect such resources. As groups grow larger, less personalized, and more formally organized, they would also be prone to shift from occasional violent disagreements between individuals to the groupwide aggression that we mistakenly take for granted as representative of humankind’s naturally warlike state.75

  Although it is unclear just how much fighting and mayhem went on among our Pleistocene ancestors (it probably varied a lot with local circumstances) or just when organized warfare first appeared, what is clear is that once local conditions promote the emergence of warlike societies, that way of life (as well as the genes of those who excel at it) will spread.76 Altruists eager to cooperate fare poorly in encounters with egocentric marauders.77 So this is the puzzle: How was it possible that the more empathic and generous types of hunter-gatherers developed, much less ever flourished, in ancient African landscapes occupied by highly self-centered apes?

  This is a profoundly relevant question. Were it not for the peculiar combination of empathy and mind reading, we would not have evolved to be humans at all. This poor teeming planet of ours would be under the thrall of one of the other ten or so branches of the genus Homo, populated by some alternate variation on the themes of bipedal hunting apes with large brains, elaborate tool kits, and an omnivorous diet who entered the fray over the preceding two million years. Without the capacity to put ourselves cognitively and emotionally in someone else’s shoes, to feel what they feel, to be interested in their fears and motives, longings, griefs, vanities, and other details of their existence, without this mixture of curiosity about and emotional identification with others, a combination that adds up to mutual understanding and sometimes even compassion, Homo sapiens would never have evolved at all.78 The niches humans occupy would have been filled by very different apes. This is where intersubjectivity comes in. But what was the impetus? Given the ecological circumstances of early hominin populations, do we really want to rely on out-group hostility and reflexively genocidal urges as the explanation of choice for the emergence of peculiarly prosocial natures?

  According to the best available genetic reconstructions of our own species, the founding population of anatomically modern humans who left Africa some time after 100,000 years ago numbered 10,000 or fewer breeding adults, a rag-tag bunch preoccupied with keeping themselves and their slow-maturing children alive. The chimpanzee genome today is more diverse than that of humans probably because these once highly successful and widespread creatures descended from a more diverse and numerous founding stock than modern humans did.79 These days, chimpanzees are in far more immediate danger of extinction than are humans, but 50,000 to 70,000 years ago the situation was reversed. Only barely, by the skin of their teeth, did the original population of Homo sapiens avoid the same fate—extinction—suffered by all the other hominins.

  Apart from periodic increases in unusually rich locales, most Pleistocene humans lived at low population densities.80 The emergence of human mind reading and gift-giving almost certainly preceded the geographic spread of a species whose numbers did not begin to really expand until the past 70,000 years. With increasing population density (made possible only, I would argue, because they were already good at cooperating), growing pressure on resources, and social stratification, there is little doubt that groups with greater internal cohesion would prevail over less cooperative groups. But what was the initial payoff? How could hypersocial apes evolve in the first place?

  As Tomasello argues, the capacity to be far more interested in and responsive to others’ mental states was the critical trait that emerged and set the ancestors of humans apart from other nonhuman apes. Capacities for learning from each other and sophisticated cooperation that flowed from enhanced mind reading led to unprecedented advances in the realm of culture and, with cumulative cultural knowledge, in technology—gradual advances that eventually took on a life of their own. As a consequence, humans were able to prosper, develop networks of exchange to survive where otherwise they could not, and eventually to spread around the globe. The rest is history—as well as our species’ best hope for having a future. But recognizing this unusual human capacity for caring about what others think, feel, and intend begs the question: How did it happen that cognitive and emotional traits with such obvious benefits for enhancing survival came to characterize only this single surviving line of apes? How could natural selection ever have favored the peculiarly empathic qualities that over the course of human evolution have served our species of emotionally modern humans so well?

  Natural selection has no way to foresee eventual benefits. Future payoffs cannot be used to explain the initial impetus, that is, the origin of mind reading. I don’t doubt (as book after book describing “human nature and the origins of war” remind us) that “a high level of fellow feeling makes us better able to unite to destroy outsiders.”81 But if hypersociality helps one group beat out another, would not in-group cooperation in the service of out-group competition have served other apes (for example, warring communities of chimpanzees) just as well? Indeed, we already know that chimpanzees perform best on tests requiring a rudimentary th
eory of mind when they are in competitive situations.82

  When I confided these theoretical difficulties to Polly Wiessner, she acknowledged worrying about the same problem. This expert on hunter-gatherer social relations, who as it happens was raised in Vermont, proceeded to recount the following anecdote about a lost tourist asking directions from a local: “If I were aiming to go there,” replied the crotchety New Englander, “I would not start out from here.”83 There it was, my problem in a nutshell. Starting out with an ape as self-centered and competitive as a chimpanzee, how could natural selection ever have favored the aptitudes and quirks of mind that underpin the high levels of cooperation found in humans? How could Mother Nature concoct such a hypersocial ape starting with such an impulsively selfish one? The answer, as we will see, is that she didn’t start from there.

  THIS BOOK

  Mothers and Others is about the emergence of a particular mode of childrearing known as “cooperative breeding” and its psychological implications for apes in the line leading to Homo sapiens. As defined by sociobiologists and discussed in a rich empirical and theoretical literature, “cooperative breeding” refers to any species with alloparental assistance in both the care and provisioning of young. I will propose that a long, long time ago, at some unknown point in our evolutionary history but before the evolution of 1,350 cc sapient brains (the hallmark of anatomically modern humans) and before such distinctively human traits as language (the hallmark of behaviorally modern humans), there emerged in Africa a line of apes that began to be interested in the mental and subjective lives—the thoughts and feelings—of others, interested in understanding them. These apes were markedly different from the common ancestors they shared with chimpanzees, and in this respect they were already emotionally modern.

  As in all apes, the successful rearing of their young was a challenge. Mortality rates from predation, accidents, disease, and starvation were staggeringly high and weighed most heavily on the young, especially children just after weaning. Of the five or so offspring a woman might bear in her lifetime, more than half—and sometimes all—were likely to die before puberty. Unlike mothers among other African apes, who nurtured infants on their own, these early hominin mothers relied on groupmates to help protect, care for, and provision their unusually slow-maturing children and keep them on the survivable side of starvation.

  Cooperative breeding does not mean that group members are necessarily or always cooperative. Indeed, as we will see, competition and coercion can be rampant. But in the case of early hominins, alloparental care and provisioning set the stage for infants to develop in new ways. They were born into the world on vastly different terms from other apes. It takes on the order of 13 million calories to rear a modern human from birth to maturity, and the young of these early hominins would also have been very costly. Unlike other ape youngsters, they would have depended on nutritional subsidies from caregivers long after they were weaned.84

  Years before a mother’s previous children were self-sufficient, she would give birth to another infant, and the care these dependent youngsters required would be far in excess of what a foraging mother by herself could regularly supply. Both before birth and especially afterward, the mother needed help from others; and even more importantly, her infant would need to be able to monitor and assess the intentions of both his mother and these others and to attract their attentions and elicit their assistance in ways no ape had ever needed to do before. For only by eliciting nurture from others as well as his mother could one of these little humans hope to stay safe and fed and to survive.

  No one has a machine to go back in time to observe what childrearing in the Pleistocene was like or to record the consequences of novel developmental trajectories. But what we do have is evidence from a diverse array of primates and other animals that is relevant to understanding why other group members would begin to help and how cooperative breeding evolves. We also have a growing body of information about contemporary gathering-hunting people, revealing for the first time how many others have to pitch in if a nomadic foraging mother is going to rear her offspring to breeding age. To reconstruct the deep history of Pleistocene family life and the development of youngsters dependent on both mothers and an array of others, I will be drawing on information, much of it quite new, from comparative primatology and the ethnographic study of childhood in foraging societies, along with cognitive psychology, neuroendocrinology, and the flourishing new field of comparative infant development as well as from paleontology, sociobiology, and human behavioral ecology. Published 150 years after Darwin’s Origin of Species, this book, like the far greater one that inspired it, is written as “one long argument.” As evidence-based and consistent with evolutionary theory as I can make it, this book is an attempt to reconstruct long-ago events detailing the emergence of emotionally modern humans, step by Darwinian step.

  Before turning to a detailed examination of the cooperative breeding hypothesis that I favor, let’s begin by considering some of the main alternative hypotheses that have been proposed to explain why intersubjectivity evolved in the line leading to Homo sapiens.

  * An alloparent (from the Greek “allo-” for “other than”) refers to any group member other than the parents who helps them rear their young. Since it is often impossible to assign paternity, I often opt for “allomother,” a term which might or might not include the father.

  2

  WHY US AND NOT THEM?

  Had humanity not been the interested party, we would have been the fifth great ape.

  —Richard Leakey (2005)

  I sat gazing at a chimpanzee who sat on the other side of a fence, gazing at me. As a psychoanalyst, I have been taught to analyze the countertransference, which means that I try to formulate how this animal is making me feel. So I sat there and tried my very hardest to do that. I felt . . . something missing, I could not connect. I was reminded of the experience one sometimes get when relating to a child with autism . . . It was as if this chimp was not at home, mentally speaking.

  —Peter Hobson (2004)

  Are humans just another ape, or an utterly different ape? No one can map the DNA of a chimpanzee, watch a bonobo striding upright on two legs or concentrating and excelling at object manipulations, or look a gorilla or orangutan in the eye and fail to be impressed by how similar we are to them. From Darwin onward, scientists have traced the anthropoid origins of emotions, ranging from satisfaction, loyalty, and joy to embarrassment, anxiety, shame, anger, and disgust.1 Thus when the paleontologist Richard Leakey looks deeply into the eyes of a chimpanzee, he sees a kindred creature. And well might a psychiatrist like Peter Hobson wonder, “What is he thinking?” But when our hairy cousin returns that gaze, the film in his camera seems different. Thus, whereas Leakey the paleontologist emphasizes the profound homologies between humans and other apes, Hobson the psychiatrist is more struck by differences between two closely related species.2 Both are right.

  Primatologists familiar with chimpanzee behavior will be quick to point out that Hobson’s simian acquaintance scarcely knew him from Adam. Had Hobson actually had a prior relationship with that chimpanzee, the eyes returning his gaze might well have seemed less blank.3 Certainly there are circumstances when chimpanzees sense how someone else feels. Chimpanzees yawn when someone else does, just the way humans do, and they seem to understand what to do when another ape seeks help, paying special attention to licking the inaccessible places, for example, when tending a fellow chimpanzee that has been wounded by a leopard. Apes seem especially helpful toward offspring or younger siblings.4 When it occurs, empathetic-seeming behavior by apes makes a huge impression. Audiences are riveted when the renowned ethologist Frans de Waal tells the story of Kuni the captive bonobo who picked up a stunned starling. After a concerned keeper urged the ape to let the bird go, the bonobo made abortive attempts to get it to fly before climbing high in a tree where she “carefully unfolded its wings and spread them wide open” as she threw the bird up into the air.5 But as de
Waal himself stresses, we have to be cautious about interpreting what we see.

  Yes, human-reared chimpanzees test surprisingly well at simple cooperation, like helping someone else extract something.6 But in spite of their rudimentary understanding of what someone else is trying to do, these apes’ capacity for attributing separate mental states to others (or else the extent to which they care to do so) seems limited. Furthermore, such intersubjective capacities as they can muster emerge more readily in competitive than in cooperative situations.

  Consider one recent experiment. A psychologist placed food in various places, some items in full view of a dominant chimpanzee, others out of his sight, while a subordinate in an adjacent cage was allowed to watch. When both were released into the cage with the food, the subordinate took advantage of his advance knowledge to bypass food in plain sight and make a beeline for the hidden treats.7 When tested in a non-competitive situation, however, chimpanzees seem less concerned about others, especially if they do not have a previous relationship. Compared with human children, chimpanzees have excellent spatial memory and are very good at discriminating quantities, but they test far less well on social learning or reading nonverbal cues having to do with hidden rewards or intentions.8

  The strongest evidence for chimpanzees’ lack of regard for others comes from experiments by the UCLA primatologist Joan Silk. As a Stanford undergraduate, Silk went to the Gombe Stream Reserve of Tanzania to study mother-infant behavior among chimpanzees. Subsequently, she became known for her work on macaques, baboons, and humans. But she never forgot her early experiences with chimpanzees. She knew that they sometimes engage in collective activities like hunting, and they share food under special circumstances, console a victim of aggression with a hug, or stay near a dying relative. Still, the extremely analytical Silk was skeptical of claims about chimpanzee empathy. She thought up a clever experiment to test just how eager they would be to help when given an opportunity to do so at no particular cost to themselves. Silk and her team deliberately opted to use individuals who were familiar with one another but not close relations.