Paleofantasy: What Evolution Really Tells Us about Sex, Diet, and How We Live (26 page)

This is more or less what anthropologist Lee Gettler and his colleagues found in a long-term study of over 600 men in the Philippines.
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The scientists examined the men’s levels of testosterone, the sex hormone behind many male-typical behaviors and physiological processes, before and after the men became “partnered fathers,” as they put it. They also determined how much time each subject spent interacting with his child.

As Gettler and his coworkers predicted, men with higher testosterone levels at the start of the study were more likely to have become partnered fathers at the follow-up four and a half years later. But then something interesting happened. The fathers showed a dramatic decline in testosterone compared with both their own single, prepaternal levels and the levels of the men who had remained single. What’s more, testosterone was lowest in those men who spent at least three hours a day caring for their son or daughter, after controlling for the effects of sleep loss and other variables.

This study is illuminating for several reasons. First, it uses longitudinal data, meaning that the same men were remeasured, allowing them to be used as their own controls. This kind of analysis is superior to one in which a group of fathers is compared with a group of single men, because a number of confounding factors could have caused a difference in hormone levels—say, if the single men were more likely to have used particular types of medication, or the fathers were from different socioeconomic classes. Second, the study indicates a finely tuned back-and-forth between a person’s physiology and behavior. Cues from the environment can influence the hormone levels of fathers as well as mothers. The scientists suggest that although seeking a mate requires characteristics that may be antithetical to being a good father, it is, in fact, possible to have it all, and testosterone acts as the mediator. Third, as anthropologist Peter Gray pointed out in a commentary accompanying the article, the research “serves as a nice case study of the relevance of evolution to everyday human life.”
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The trade-off between mating and parenting is one that is predicted by evolutionary theory, and it means that a longing for new sexual partners might not be part of our heritage.

Gettler acknowledges that the degree of care by fathers is and always has been affected by many things, including geography, the way people make a living, and the importance of social class. He, along with other anthropologists, agrees that even when they do not hold or watch over children, fathers are often essential in providing food to their families. But Gettler is not willing to conscribe fathers to bread (or meat) winning alone. In a 2010 paper, he speculates that our image of early
Homo
society with a strict sexual division of labor may be incorrect, and that instead, “males, females, and young frequently traveled together to forage and scavenge at the same resource sites.”
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It is true that this pattern is not commonly seen among modern-day foragers, but if it occurs, it also solves another problem: who carries the baby?

As discussed already, being a hairless bipedal animal with a helpless infant is daunting, especially in an environment where you need to move around to make a living. One solution, as proposed earlier, is to construct slings or other technological gadgets to transport babies, but another, simpler, one is to have dad do the carrying. This solution not only frees mom’s hands, but gives her a rest. From fossil remains, Gettler calculated the body size and the calories per hour that males and females of several early hominins would have expended in walking, and then extrapolated the increase in calories that would have been used (or saved) by carrying a 15-pound infant.
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By having the father take over this task for some portion of the day, a mother could conserve her energy, and potentially be ready to conceive and bear another infant sooner, which would mean higher fitness for both parents.

Such optimistic scenarios notwithstanding (maybe those baby-wearing New Age dads are actually somewhat retro), fathers probably were not the sole sharers of child care in our evolution. For one thing, they can be unreliable, as mentioned already, both in the resources that they can provide and in the likelihood that they will stick around after a child is born. Jeffrey Winking and Michael Gurven examined the effect of fathers deserting their children to marry and have children with a new—and younger—wife on the survival of those original children, as well as on the fitness of the men themselves.
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The researchers constructed a model using data on fertility rates and survival in four hunter-gatherer populations, as well as one agricultural group. They found that the men would not lose much in the way of child survival, and in fact had higher reproductive success overall, if they married a second wife who was just a couple of years younger than the first. Winking and Gurven’s model makes a number of assumptions, such as that a new woman is probably waiting in the wings, but the bottom line is that selection may not have favored caring fathers simply to ensure the survival of their children.

If fathers are not the key, who is? A common answer has been grandmothers. Grandmothers are popular babysitters in many cultures—a choice that, besides being convenient, turns out to make good evolutionary sense. In the 1990s, anthropologist Kristen Hawkes proposed that maternal grandmothers were essential in our early evolution, because, being past their own reproductive years, they could help their daughters with the demands of young motherhood. In fact, she and others suggested, such duties could even explain an evolutionary puzzle: menopause, which otherwise seems like a peculiar attribute of humans. If having offspring is the way to evolutionary success, why would any organism live long past the time when it could reproduce?

At this point many people object that menopause would have been a nonissue in our early history, because the average life span was far less than it is today. While this is true, those averages can be deceiving, as I discussed in the Introduction; a high rate of infant mortality will make the average age at death low, even if a person who survives past twelve has a fairly high chance of making it to sixty-five. Indeed, a woman in a contemporary hunter-gatherer society who reaches menopause is very likely to live well past sixty, even without modern medicine.

According to what is called the grandmother hypothesis, these postmenopausal women were part of the alloparental team that enabled humans to keep our short interbirth interval and not have to rely on fathers for care. Having caregivers who did not have young children of their own would thus be favored by selection, leading to the evolution of menopause itself. Because of the lack of certainty that a given child is indeed genetically related to a given man, maternal, rather than paternal, grandmothers are thought to be particularly likely to fill this role. Caring for children pays off evolutionarily only if those children share your genes, and for fathers—and their mothers, the paternal grandmothers—some uncertainty of that relationship exists, even if the actual frequency of misassigned paternity is rather low. Hence, helpful maternal grandmothers are always contributing to the welfare of their genetic relatives, while paternal grandmothers may not be.

Proximity is another reason that grandmothers are on the list for helping out. In some societies, young women move to their husband’s village or tribe when they marry, while in others the reverse occurs and women stay with their relatives while the men move. Hrdy argues that societies of the latter kind, which obviously favor maternal grandmothers as alloparents, were more common before industrialization.
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Whether grandmothers are truly linchpins of cooperative breeding, or their help is what drove the evolution of menopause, is still debated. Mace and Sear conclude that maternal grandmothers in their survey unequivocally helped their grandchildren survive,
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and a study of modern Dutch families showed that when grandparents helped with child care, parents were more likely to go on to have more children.
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The Dogon, of course, are evidence that grandparents are not uniformly helpful. As an alternative explanation, Michael Cant and Rufus Johnstone propose that, rather than grandmotherly help, the critical factor in menopause evolution was competition between the generations for resources to use in reproduction.
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Edward Hagen and H. Clark Barrett found that among the Shuar people of Ecuador—horticulturalists who rely on plantain and sweet manioc—adolescent boys were the ones who helped children grow up, rather than their sisters or grandmothers.
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Similarly, among two other hunter-gatherer societies in South America, men, not women, provided help to youngsters, albeit by giving them food rather than by cuddling them.
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Anthropologists will doubtless continue to debate the generality of grandmotherly help, along with cooperation in child rearing. A more important point, however, is that the image of the Pleistocene family as one of mother and father with their dependent offspring, operating largely by themselves, is inaccurate. And therefore the idea that we ourselves are best suited to a nuclear family life is misguided.

Crying, and sleeping, through the night

Thus far, I have been focusing on the evolution of children from the point of view of the parents, and assuming that once confronted with an infant, any mother—or alloparent—will know how to care for it. What about the baby’s perspective? Advocates of “attachment parenting,” “baby wearing,” “cosleeping,” skin-to-skin contact right after birth, and other supposedly new forms of parenting often suggest that these are more natural ways to care for children. “More natural” here presumably means that they are more likely to have been the ways that infants (and their parents) evolved.

Taking this idea to its more or less logical extension, some anthropologists have proposed the field of evolutionary pediatrics, which takes an evolutionary perspective to child raising. Just as evolutionary or Darwinian medicine suggests that we see increasing rates of “diseases of civilization” such as diabetes or hypertension because of the mismatch between our Paleolithic environment and our modern one, evolutionary pediatrics proposes that infants have the same needs that they had hundreds of thousands or millions of years ago, and that we have to find ways to satisfy these needs in an industrialized society. One champion of this approach, James McKenna from the University of Notre Dame, bluntly states, “We are pushing infant adaptability (and indeed maternal adaptability) too far, with deleterious consequences for short-term survival and long-term health.”
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What does an evolutionary mismatch mean for a baby, who is not able to choose between high-fructose-corn-syrup-laden cookies and a more healthful option? Infants eat, sleep, and excrete, and it might seem that there is little that can be done to alter this pattern; many parents have marveled at the apparently primal needs of their newborns. Surely, if anything about human life “ ’twas ever thus,” including back in the Stone Age, it should be infancy.

One clue that this assumption might be false comes from a familiar source: cross-cultural data on parenting, including information about infancy in hunter-gatherer or horticultural peoples. Parents are usually quick to acknowledge that not all babies behave the same, but they don’t necessarily recognize that babies from the same culture often have characteristic behaviors, behaviors that seem to arise from societal expectations. Cultural practices influence how, where, and when infants sleep, for example. We often imagine that babies move to their own rhythms, and that our ancestors must have responded to their infants in much the same way that we do. But this turns out to be incorrect; even among modern societies, some very basic aspects of infant life can be tremendously variable.

First off, sleeping. As the popularity of the not-for-children book
Go the F**k to Sleep
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attests, sleeping is a battleground for many parents; their children don’t sleep long enough, won’t go to sleep at the appropriate time, or cry inconsolably at intervals during the night. Is this natural?

Perhaps not. In Western industrialized societies, babies are encouraged to sleep in a way that they are not anywhere else—namely, alone in a room. In her fascinating book
Our Babies, Ourselves
, anthropologist Meredith Small points out that the Western emphasis on babies being independent from an early age is unheard of in most other cultures.
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Babies are in near-constant physical contact with their mothers or an alloparent in virtually all foraging societies, where they can feed whenever they like; Small notes that the concept of nursing “on demand,” or whenever the infant seems to want to be fed, as opposed to feeding on a fixed schedule, is foreign to these parents, since no one is demanding anything or acceding to demands. Small and McKenna also find baby monitors, devices that allow distant parents to hear their children crying or fretting, strange inventions; McKenna believes that babies evolved to sleep in social environments, and suggests that infants would be better served if the monitors conveyed the reassuring sounds of the parents’ voices and activities to the baby, rather than vice versa. A study of parenting among the Maya of Latin America found that separating infants from their mothers to sleep was viewed as child abuse or neglect by Mayan mothers.
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Western parents often feel that a “good” baby is one who soon sleeps through the night, rather than waking frequently, but this ability may be common only among formula-fed infants and those who are placed on their stomachs to sleep. Sleeping on the stomach has been linked to sudden infant death syndrome (SIDS), and parents are now counseled to place babies on their backs, but the expectation of early independence at night is still widespread. Parents are also advised not to give in if their children wake frequently and demand attention.

We can trace the history of the Western concern that infants sleep alone back to a complex mixture of Freudian thought, concern about medieval mothers deliberately smothering their children, and other kinds of parental advice. McKenna and his colleagues examined the widespread belief that cosleeping—having an infant either in the same bed as the parent or in a bassinet or other device attached to the parental bed—is linked to SIDS, and found no support for the notion.
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Instead, they advocate cosleeping as a means to strengthen the bond between mother and child and to ensure that the child breathes better and feeds appropriately. The environment, they say, should allow the infant and caregiver an opportunity to sense each other and continually adjust their positions and activities.