Among naturalists, the terms “cooperative breeding,” “alloparenting,” and “helpers at the nest” describe this kind of behavior, and the evolutionary success of some species depended on it, but it emerged only gradually as a possible explanation for the triumphs of our own. The roots of this idea can be found in Jane Lancaster’s observation that only humans provide for their young after weaning, and that this must have helped make earlier weaning possible.9 Our ape cousins breast-feed until age four or five and then forage on their own; human hunter-gatherers breast-feed for two-and-a-half to three years, with weaning foods replacing milk. It’s difficult to overstate the importance of shortened nursing; it leads to shortened spacing between births, which leads to more rapid population growth—a possible explanation for how we edged out the other primates.
But mothers could not have done this alone. Lancaster and other anthropologists believed it was the male members of the species—seduced, cajoled, and bargained into fatherhood—who supplied the high-protein, high-energy animal flesh that helped sustain the weanling. Kristen Hawkes, studying Hadza hunter-gatherers in Tanzania, thought the solution to the mother’s dilemma was the nonreproducing grandmother, who in the course of evolution had extended her lifespan long beyond her fertility so as, Hawkes hypothesized, to help her daughters rear their young.10 And Beatrice Whiting, one of the first cultural anthropologists to do systematic cross-cultural studies of childhood, believed it was the child nurse, usually an older sister but often a cousin or young aunt and sometimes even a brother, who helped bear the burdens of child care for mothers, making life, work, and further reproduction possible.11
Yet even the closest mother-infant relationships are embedded in a dense social environment, as in this description of !Kung hunter-gatherer infants in Botswana, which Hrdy quotes:
From their position on the mother’s hip they have available to them her entire social world…. When the mother is standing, the infant’s face is just at the eye-level of desperately maternal 10- to 12-year-old girls who frequently approach and initiate brief, intense, face-to-face interactions, including mutual smiling and vocalization. When not in the sling they are passed from hand to hand around a fire for similar interactions with one adult or child after another. They are kissed on their faces, bellies, genitals, sung to, bounced, entertained, encouraged, even addressed at length in conversational tones long before they can understand words.12
The mother does not have to assign the care of the baby to an older child, nor does the grandmother have to take over for there to be enough support to make life easier and more pleasant for the mother. The fact of a mother at home alone with an infant or a toddler is a new one in human experience, and it may not be “natural” for either.
This becomes clearer with careful measurement. Ann Cale Kruger, a developmental psychologist who analyzed !Kung responses to crying, found that in timed, coded behavioral observations someone other than the mother helped respond to a baby’s cry in most cases.13 Even the longest crying bouts, those over thirty seconds (!Kung infants aren’t left to cry very long), evoked a nonmaternal effort half the time. However, she also found that the number of longer bouts of crying in which the mother was not involved was zero. These findings confirmed that although mothers are not alone in meeting the challenges of baby care, they can have a uniquely important role.
Could Hrdy’s cooperative breeding model be compatible with Bowlby’s original notion of the centrality of a single caregiver? Studies of infancy in other hunter-gatherers strongly suggest that it is.14 Research on Efe hunter-gatherers in the African rainforest found that infants are given extensive nonmaternal care, even to the point of being breast-fed at times by women other than the mother; yet mothers clearly predominate, especially at the age when attachments are forming. The same is true of the Aka, hunter-gatherers of Cameroon; they have the most involved fathers of any culture, but mothers still predominate. Grandmothers also matter in all such foraging groups, but not, on average, nearly as much as mothers.
Does this mean that only mothers can care for infants? Certainly not. Even Bowlby said “mother or primary caregiver.” His own denial of the importance of breast-feeding in forming and sustaining attachment clearly suggested that any caring person could do the job. But he believed that one person must be more important than others in order for attachment to take a normal course. This claim, as yet, has not been proved, but nothing in Hrdy’s wide-ranging account disproves it either. So it is possible to accept her claim that something like cooperative breeding or helpers at the nest was a key factor in human evolution without rejecting the idea of a primary caregiver.
What about Hrdy’s other pair of claims—that humans are uniquely cooperative among primates and that this is due to the vital evolutionary role of cooperative breeding? There is no known way to evaluate the second claim, except to say that it is reasonable. If the Darwinian imperative is successful reproduction, then an adaptive advantage as powerful as helpers at the nest could easily have been the first step toward further exceptional cooperation, and human cooperation is impressive. Chimpanzees in experiments show much less of it than we do.
But just what that cooperation means remains the subject of lively debate. Humans do more things together on a far greater scale than any species of ape or monkey. But is this owing to greater cooperative inclination or greater cognitive, communicative, and organizing ability? We read one another’s beliefs and intentions much better than any other primate does, but does this make us more cooperative or only more skilled at subterfuge and deception? Our cooperation seemingly knows no bounds, but it is at its best within one group arrayed, for defensive or destructive purposes, against another.
In her attempt to emphasize the cooperative dimension of human life—which, to be fair, she considers fragile—Hrdy tends to slight her own earlier work on such behavior as competitive infanticide and “aunting to death”—the process by which an infant is adopted by an adult, who then neglects the infant until it dies. She cites Barbara Smuts’s work on friendship in baboons, but not her meticulous and unsettling survey of male violence against females in the natural and human world. And while Hrdy refers appropriately to cooperation among the reputedly fierce Yanomamo tribe of Venezuela, we need to remember that, as the anthropologist Napoleon Chagnon documented, Yanomamo men who have killed others have more descendants than those who have not.
Indeed, rapid evolution of humans may not mainly have increased cooperation, as Hrdy concludes; 12 percent of men in Central Asia today have Y chromosomes traceable to a man who lived around the time of Genghis Khan, and more than two million men in Ireland can trace their genes to a single medieval warrior-king. These facts can be squared with an evolved tendency to cooperate, but to what degree did such cooperation take place in a surrounding environment of competition and aggression?
Charles Darwin’s own sex did not prevent him from giving females a very prominent, even governing role, in evolution. On The Origin of Species suggests that the peacock’s tail and other apparently maladaptive traits were the effects of female choice, an explanation elevated in his later The Descent of Man and Selection According to Sex to a major principle. Females can be viewed as conducting a vast breeding experiment in which males were the animals bred, and this accords females extraordinary power. But that power led to a world in which males are often pitted against one another, competing for the chance to reproduce. Of course, females also compete for mating opportunities, and they raise their sons and daughters to do the same. Perhaps experience with caregiving and the ensuing ability to discern others’ intentions makes them better at this effort, but it does not necessarily make them cooperate.
Hrdy’s gracefully written, expert account of human behavior focuses on the positive, and its most important contribution is to give cooperation its rightful place in child care. Through a lifetime of pathbreaking work, she has repeatedly undermined our complacent, solipsistic, masculine notions of what women were meant “by nature” to be. Here as elsewhere she urges caution and compassion toward women whose maternal role must be constantly rethought and readjusted to meet the demands of a changing world. Women have done this successfully for millions of years, and their success will not stop now. But neither Hrdy nor I nor anyone else can know whether the strong human tendency to help mothers care for children can produce the species-wide level of cooperation that we now need to survive.
9 Jane B. Lancaster and Chet S. Lancaster, "Parental Investment: The Hominid Adaptation," in How Humans Adapt, edited by Donald J. Ortner (Smithsonian Institution Press, 1983). ↩
10 Kristen Hawkes, "Grandmothers and the Evolution of Human Longevity," American Journal of Human Biology, Vol. 15, No. 3 (2003). ↩
11 Beatrice B. Whiting and John W.M. Whiting, Children of Six Cultures: A Psychocultural Analysis (Harvard University Press, 1975). ↩
12 Melvin Konner, "Aspects of the Developmental Ethology of a Foraging People," in Ethological Studies of Child Behavior, edited by N.G.B. Jones (Cambridge University Press, 1972). ↩
13 Ann Cale Kruger and Melvin Konner, "Who Responds to Crying? Maternal Care and Allocare Among the !Kung," Human Nature, Vol. 21, No. 3 (2010). ↩
14 For a review see Melvin Konner, "Hunter-Gatherer Infancy and Childhood: the !Kung and Others." in Hunter-Gatherer Childhoods: Evolutionary, Developmental and Cultural Perspectives, edited by Barry S. Hewlett and Michael E. Lamb (Aldine Transaction Publishers, 2005). ↩
Jane B. Lancaster and Chet S. Lancaster, “Parental Investment: The Hominid Adaptation,” in How Humans Adapt, edited by Donald J. Ortner (Smithsonian Institution Press, 1983). ↩
Kristen Hawkes, “Grandmothers and the Evolution of Human Longevity,” American Journal of Human Biology, Vol. 15, No. 3 (2003). ↩
Beatrice B. Whiting and John W.M. Whiting, Children of Six Cultures: A Psychocultural Analysis (Harvard University Press, 1975). ↩
Melvin Konner, “Aspects of the Developmental Ethology of a Foraging People,” in Ethological Studies of Child Behavior, edited by N.G.B. Jones (Cambridge University Press, 1972). ↩
Ann Cale Kruger and Melvin Konner, “Who Responds to Crying? Maternal Care and Allocare Among the !Kung,” Human Nature, Vol. 21, No. 3 (2010). ↩
For a review see Melvin Konner, “Hunter-Gatherer Infancy and Childhood: the !Kung and Others.” in Hunter-Gatherer Childhoods: Evolutionary, Developmental and Cultural Perspectives, edited by Barry S. Hewlett and Michael E. Lamb (Aldine Transaction Publishers, 2005). ↩