Mothers and Others

by Sarah Blaffer Hrdy

  Her subjects were trained to obtain edible rewards by pulling on one of two ropes. If the chimpanzee pulled the first rope, food was delivered to his own cage. If instead the chimpanzee selected the other rope, food was delivered to both the puller’s cage and the cage adjacent to him. Did it make any difference to the chimpanzee in charge whether or not the adjacent cage was occupied by another animal, also eager to be fed? The chimpanzees behaved as if they couldn’t care less whether or not their neighbor got something to eat. However, when researchers at Max Planck subsequently performed similar experiments using chimpanzees with prior relationships, they found that individuals who knew each other not only cooperated in obtaining food but kept track of “reputations.” These captive chimpanzees exhibited a preference for collaborating with others who had demonstrated that they were good at rope-pulling.9

  Additional experiments were set up at Max Planck to explicitly test Silk’s conclusions. They seemed to confirm that the chimpanzees were “almost totally self-regarding.”10 Whether or not another chimpanzee also got a reward, or failed to, was just not that important to the chimpanzee subjects in these experiments. Like Silk’s original paper, which was titled “Chimpanzees Are Indifferent to the Welfare of Unrelated Group Members,” the new Max Planck work was titled “What’s in It for Me? Self-Regard Precludes Altruism and Spite in Chimpanzees.” Both stressed the absence of spontaneous impulses to give or care about what others receive.

  Undeniably, chimpanzees, especially when they reach out a hand to beg, embrace, or kiss another, pat another on the back, comfort, or even assist a fellow group member, seem eerily like us. We are still in the early days of comparing and contrasting the cooperative tendencies of other apes with those found in humans, and the results continue to be difficult to interpret. This is why some researchers characterize chimpanzees as by nature “highly cooperative creatures,” while others focus on the fact that cooperation among chimpanzees has been documented only among specially trained chimpanzees or chimpanzees who have opportunistically learned how to cooperate under captive conditions or have been observed only when food is not involved.11

  In my opinion, there is little question that human children are less self-centered, more spontaneously cooperative, and more strongly inclined to share than chimpanzees are. But then again, children are exposed right from birth to the same sort of human models that the captive chimpanzees who do better on tests of cooperation are exposed to. Nevertheless, the experiments by Silk’s team as well as those from Max Planck and elsewhere seem to consistently show that chimpanzees—even those reared by humans—are just not terribly interested in understanding what someone else wants or intends. Unless specially trained, chimpanzees pay attention to what others know when they are competing, not when they are cooperating. By contrast, humans pay attention to others in both spheres.

  Talented researchers who often disagree continue to probe chimpanzee-human similarities and differences. Some of them may end up softening their conclusions about chimpanzee indifference. But what I do not expect to change is the contrast between the natural readiness of most people to help an unrelated travel companion (though under contemporary conditions this may be becoming less common!), and the absence of such giving impulses in apes living under natural conditions. Compared with other primates, humans are born far more eager to share the mental and affective states of others.

  So far as most psychiatrists are concerned, caring about someone else’s mental as well as their physical state (whether they might be hungry, for example) is integral to human nature. The absence of such impulses to give and share feelings (as among children who are autistic) is taken as an indicator of pathology. If humans show a compassionate interest in someone else’s mental state, it is taken for granted that these capacities are useful and in an evolutionary sense were adaptive.12 No doubt, once acquired, such traits did aid the survival of group-living animals. But the premise that intersubjectivity must have been adaptive in the environments in which humans evolved is only convincing until someone asks: So how did other, comparably defenseless, savanna-dwelling primates like baboons, patas monkeys, or vervets manage to evade the lions that stalked them? If intersubjectivity was so useful for maintaining cohesive social groups, defending one’s in-group from violent neighbors, or wiping out competitors, why didn’t other social primates (those “demonic” neighbor-stalking chimpanzees in particular) evolve such gifts as well? Why us and not them?

  LOGICALLY, LANGUAGE COMES LATER

  The first time I ever considered the question “Why humans and not other apes?” the answer seemed obvious. Surely, I thought to myself, it is our innate capacity to learn language, our unique ability to use words to express what is on our own and on others’ minds, which explains why humans can empathize with others through articulating their feelings and sharing their mental states, and which renders them capable of such effective cooperation. This is the view held by such eminent experts on chimpanzees as Jane Goodall. “What makes us human,” she remarked recently, “is an ability to ask questions, a consequence of our sophisticated spoken language . . . Once you can discuss something and talk about it in the abstract and take lessons from the past and plan for the future—that is what makes the difference.” But on further reflection, I find the focus on language unsatisfactory.13

  Unquestionably, the uniquely human capacity for language enhances our ability to connect with others and exponentially increases the complexity of the information we can convey. But language is not just about conveying information, as in warning others to “Look out!” An animal alarm call does that. Even vervets (which are Old World monkeys, after all, not even apes) have specific calls that alert conspecifics to danger and also inform them whether the threat is from the air and likely to be a predatory bird, as opposed to something scary on the ground, like a snake. Honeybees convey surprisingly precise information about the location of food (how far away and in what direction) by the type and duration of their ritualized “dance” movements. Animals have all kinds of ways of communicating information about their environment or state of arousal to other members of their species and to other species as well.14

  The open-ended qualities of language go beyond signaling. The impetus for language has to do with wanting to “tell” someone else what is on our minds and learn what is on theirs. The desire to psychologically connect with others had to evolve before language. Only subsequently do the two sets of attributes coevolve. As Hobson puts it, “Before language, there was something else—more basic . . . and with unequalled power in its formative potential.”15 If we are looking for sources of human empathy, these emotion-laden quirks of mind had to evolve before the words came along to articulate them. Even before humans began actually speaking to one another in a behaviorally modern way, their immediate hominin ancestors already differed from other apes in their eagerness to share one another’s mental states and inner feelings. In this sense, these creatures were already emotionally modern long before they became anatomically or behaviorally modern and were routinely using speech to converse with one another. The ancestors of people who acquired language were already far more interested in others’ intentions and needs than chimpanzees are. What we need to explain is why.

  EMPATHIC GLIMMERINGS AS OLD AS MAMMALS

  All sorts of animals are sensitive to those around them. Mice have emotional reactions to the pain of other mice. They respond to the writhing of groupmates by becoming more sensitive to pain themselves.16 The suffering of others is contagious, as well it should be. What is painful or alarming to another creature could well be dangerous to oneself. This is why fear is a particularly contagious emotion.

  Many kinds of animals, whether cold-blooded or warm-blooded, winged or scaled, may tend others and be sensitive to their well-being. Most such cases involve parents. Male fish sense the presence of eggs they are likely to have fertilized and fan the eggs with their tail to keep clean water circulating about them. Mother squid ensnare their own ball
ooning egg masses with long tentacles so as to brood them under the protective shadow of a mother’s body. Even mother crocodiles or rattlesnakes will linger protectively near newly hatched or live-birthed young until babies are mobile enough to fend for themselves.17 Wherever parental care evolved, it marked a watershed in the way animals perceived other individuals, with profound implications for the way vertebrate brains were structured.

  Nowhere have these cognitive and neurological transformations been more revolutionary than among mammals. Mammal mothers fall in a class by themselves. One has only to recall a mother dog returning to her litter again and again, nosing each pup, alert to distress, sensing their needs, suckling babies, keeping them warm. The postpartum human mother who checks her baby every 15 minutes to be sure he is still breathing follows in this venerable tradition of compulsive concern.

  Lactating mothers date back to the end of the Triassic, around 220 million years ago. This is when babies began to be born so helpless that mothers needed to be attuned to the smell, sounds, and slightest perturbations in the condition of vulnerable young that had to be kept both warm and fed. Since any nearby newborns were likely to have issued from their own bodies, it was adaptive for mothers to perceive all neonates as attractive.18 Mothers who had just undergone the hormonal transformations of pregnancy were especially susceptible.

  Superacute hearing was just one of many ways that selection operated on mother mammals to render them responsive to others. New modes of hearing, sensitivity to touch and odors, along with new ways of distinguishing one’s own young from others coevolved with cognitive frameworks for processing information about others.19 My favorite example dates back to the age of dinosaurs. Confronted with the special challenge of signaling distress to their mothers without attracting lizards and other reptiles who might eat them, early mammals evolved the ability to emit high-frequency sounds. To this day, mammals can still detect sounds at higher frequencies than reptiles can, and a mouse pup that has strayed from its mother’s nest will attract her attention by emitting ultrasonic squeaks that almost no one else can hear.20

  So, while their mothers were evolving to be more sensitive to others, baby mammals were evolving too. Natural selection favored babies who were sensitive to their mother’s body warmth and smells, able to squirm close to her and latch onto her teats, and capable of signaling effectively (and safely) when separated. It is no accident that the first regions of the neocortex to form in utero are those that eventually represent and control sucking actions by the mouth and tongue. Once a baby is born, wriggles close to his mother, and locates a nipple, he will need to wrap his lips around it, latch tight, and suck so as to stay fed and, just as importantly, to further stimulate his mother’s nurturing impulses. The tugging at her nipples stimulates the production of prolactin along with a surge of the neuropeptide oxytocin, with its pleasurable and soothing effects.21

  Humans have brains specially adapted for sympathetic interactions and the forging of relationships. At birth, an enormous amount of brain tissue, especially in the neocortex, is already allocated to processing faces, facial expressions, gestures, and vocalizations of others. The processing of this information is also motivated and stimulated by older subcortical sections of the brain that are related to the emotions and memories of earlier interactions. (Trevarthen 2005)

  Stimulating and conditioning its mother, making sure that she becomes addicted to nurturing, is actually a mammalian baby’s first critical, if unconscious, mission. The neocortex, which first evolved among mammals and overlays older, reptilian portions of the brain, serves as the control center of the nervous system.22 The neocortex equips baby mammals to form attachments to their mothers and helps get their mothers to bond with them. In time, the baby’s neocortex will expand and develop into the main decision-making area of the brain. But it will also continue to equip grown-up mammals to bond with babies and to form multifaceted relationships with others.23

  This requirement for mothers to bond with babies, and babies with mothers, meant that mammals’ brains were designed for the formation of relationships in ways that the brains of other animals are not. The need for mothers to anticipate the needs of offspring is integral to several of the hypotheses that have been proposed to explain the evolution of mind reading. Prime among these is the “mind-reading mums” hypothesis. An important alternative hypothesis centers on the need of competitive social creatures to manipulate others, known as the “Machiavellian intelligence hypothesis.” Both merit serious consideration.

  THE MIND-READING MUMS HYPOTHESIS

  The first social bonds ever forged were between a mother and her offspring. Her need to look out for vulnerable young remains the most widely accepted explanation for why, in most mammalian species, females are more affiliative and socially responsive than males are, even though there are important exceptions, as we will see in the next chapter. Such differences in sex roles are especially well documented in Old World monkeys.24 Among langur monkeys, for example, females at every life phase are more attracted to infants than males are. Even females far too young to be mothers respond to infantile vocalizations, and they eagerly approach, attempt to touch, hold, inspect, and carry infants. More than 99 percent of all attempts to take babies involve females.25 Except in extreme situations, and then only briefly to rescue (or maul) them, male langurs never carry babies.26 Not only do more responsive mothers make better mothers, but among some monkeys, such as savanna baboons, the more affiliative a female is and the more social contacts she maintains, the higher the probability that her offspring will survive.27

  Although less clear-cut and also far more difficult to interpret due to the myriad ways behavior gets shaped by cultural expectations, sex differences in caretaking have also been observed in humans. In Western society, little girls are expected to be more socially responsive and affiliative than little boys are. Whether because of such social expectations or because of innate differences, girls seem more likely than boys to form secure relationships with their care providers, and girls more readily form secure attachments to allomothers, according to recent research done in Germany.28 As early as two years of age, little girls are more likely to comfort others in distress than little boys are.29 It’s not that little boys do not comfort others, for they do. Rather, it usually takes stronger signals of distress to elicit their sympathy.30

  Childhood differences in sensitivity to others, and particularly to their signs of distress, persist into adulthood and have been documented in new parents. The Canadian psychologist Alison Fleming has been one of the pioneers in this area. She and her colleagues found that it takes more urgent-sounding cries to get a father to respond to a fretting newborn than it does a mother.31 Women also seem to be more sensitive than men are (that is, quicker and more accurate) when reading facial expressions.32

  Impressed by such reports, the New Zealand psychiatrist Raewyn Brockway proposed that highly intuitive moms not only perceive what irks their babies—a skill that enhances their ability to care for them—but are also better equipped to guide immatures as they acquire survival-enhancing skills. Mind reading is advantageous to mothers, Brockway argues, because “good teaching utilizes an empathic awareness of the infant’s point of view, both physical and psychological.” Over the course of human evolution there would have been selection for “smarter, more efficient mothering or different kinds of learning, or perhaps, most critically, in different kinds of teaching. Even the simplest components of our current theory-of-mind capacities would have been useful for promoting the survival of offspring.”33

  Sensible as it seems to argue that women evolved to be more intuitive and empathetic than men because mothers need to be more sensitive to the needs of their infants, by itself this argument cannot account for intersubjective aptitudes that appear to be uniquely human. All sorts of mammals enter the world helpless and vulnerable, none more so than baby apes. Possibly their mothers become conditioned to associate specific responses with calmer outcomes, or th
ey may have some conscious sense of what their babies are and are not capable of and what they need. In any event, all Great Ape mothers in the wild are both extremely wary of their surroundings and extraordinarily responsive to the slightest sign of discomfort in their infants, swiftly adjusting them and holding them close.

  Chimpanzee, orangutan, and gorilla mothers are more single-mindedly devoted than human mothers are, and for a much longer period of time. Their offspring would benefit from having gifted teachers sensitive to their pedagogical needs, just as human children do.34 As Brockway readily acknowledges, even chimpanzee mothers will model appropriate skills, and in doing so display sensitivity to the limitations and learning needs of apprentices practicing important subsistence tasks. Yet apes do not teach or learn from others nearly so readily as humans do, and typically not at all.

  For example, in many areas of Africa, fat-rich kernels from cracked nuts are a very important food for both humans and other apes. During seasons when nuts are available, a typical chimpanzee will average around 3,450 calories per day from this resource. But it takes years of trial and mostly error to master the technique of nut-cracking. The faster they learn this skill, the better fed young chimpanzees and young humans will be.35 Well-nourished youngsters can also be weaned sooner without the risk of starvation, leaving mothers more time to keep themselves fed. Earlier weaning and better nutrition for the mother translate into a shorter interval between the last birth and the next conception. Over a lifetime, such cumulative advantages contribute to higher maternal reproductive success. Over generations, quicker mastery of foraging techniques will mean evolutionary advantages for that lineage.