Menopause is rust. It's the system breaking down, a sign of the past catching up with you, not a well-wrought mechanism to help you shape your family's future. I loved the grandmother hypothesis, but it was time to put that pet theory out to pasture, right next to the naked ape with her rumped-up chest.
Then I learned about Kristen Hawkes and the Hadza and the Grandmothers of Invention, movers and shakers and humanity makers.
Let's start with the facts. Data nearly killed Grandma, and so it is by data that she must be revived. Hawkes and her colleagues were meticulous about collecting data on the Hadza. They spent months charting the hour-by-hour activities of ninety individuals, half male, half female, ranging in estimated age from three to more than seventy. They noted who shared food with whom and under what conditions. They weighed their subjects regularly to see who was gaining and who losing during any given season. Through such efforts, the anthropologists could measure the meat of the matter, to determine whether the foraging exertions of person A made a difference to the nutritional status of those with whom she or he shared the pickings. The researchers found beautiful linear correlations between effort and result. Hadza children start foraging in the bush at a remarkably early age—often as young as three—but they can't fend for themselves entirely. Until puberty, they depend on adults for about half their food. The mother is usually the one who gives them what they can't get. As the anthropologists saw, the efforts of the mother are reflected on the scale: the harder she forages, the more weight her children gain.
However, that correspondence disappears whenever the mother has a newborn to feed. A nursing woman continues to forage, but with much less to show for it. Not only does the infant slow her down, but lactation is costly, requiring about 600 calories a day to support, which means that the mother must eat most of what she reaps. She can't afford to share with a whimpering four-year-old. During breastfeeding, then, the association between a mother's foraging effort and the weight of her older children disappears. The two factors are uncoupled. Instead, the welfare of the weaned child shifts to another female—usually the mother's mother, but if she's not around, an older aunt, a great-aunt, or, once in a while, the mother of the children's father. Suddenly the exertions of Grandma, or her equivalent, are reflected in the children's weight gains or losses. The harder the grandmother gathers, the more pounds the children reap. The faster the children grow, the stronger and more resilient they become, and the more likely they are to reach adulthood and add greatness to Grandma in name as she has it in will.
And now a pivotal point: the older females are flexible. They're strategic. They don't restrict their assistance to children and grand-children. They help any young relatives who need their help. When Hill and Hurtado studied the Ache of Paraguay, they asked, How much do older women assist their grown children and grandchildren, and do their contributions make a significant difference to those children and grandchildren? (Answer: not enough to explain menopause.) Hawkes and her colleagues cast a wider net. They had to. The Hadza women were spending too much time to ignore outside the cozy nexus of the immediate family. If an older woman didn't have a daughter to help, she helped the daughter of a sister. If a nursing woman's mother was dead, she turned to an older cousin and threw her existing children on the cousin's mercy, and the cousin obliged if she could, if she was past the time when she had to worry about infants of her own.
"Senior females allocate effort with the biggest fitness bang," Hawkes told me. "If they don't have nursing daughters of their own to help, they find other relatives to help. With strategic critters like ourselves, you'd expect behavioral adjustments like that. You'd expect that natural selection would favor adjusting help to where it's needed most.
"If you looked at the Hadza and considered only the impact that a postmenopausal woman had on the reproductive success of her children," she added, "you'd underestimate the effects of senior help by a huge amount." But if you take into account the seniors' contributions to the nutritional status of all young relatives, suddenly the old ladies are worth it. They are enhancing their total genetic fitness to the point where they don't need late-stage maternity to make their Darwinian mark. Another baby or three would just get in the way of their foraging.
Where, you might ask, are the Hadza men in this picture? Why are they not providing for their wives and children, as men supposedly have always done, so giving rise to the nuclear family and division of labor by sex? The Hadza men work, all right. They hunt, and the meat they bring back serves as a meaningful source of calories for the whole group. But hunting is an irregular enterprise and often unsuccessful; you can't count on it for your daily bread. By rights, hunter-gatherers should be called gatherer-hunters. In addition, when Hadza men make a killing, they can't help themselves: they show off. They're big men, and big men share. They share with allies they're seeking to woo or enemies they want to appease. They share with girls they're trying to impress and children who throng to the carcass. In the end, very little of the meat finds its way to the mouths of the hunter's family. The Hadza pattern is not unique. Among many traditional societies, hunting is a political rather than a personal occupation. "Hunting supplies a collective good from which all benefit, regardless of their relationship with the hunter," Kristen Hawkes and her coworkers have written. "It is women's foraging, not men's hunting, that differentially affects their own families' nutritional welfare." Women's foraging keeps their families afloat, and older women can forage as effectively as their daughters—more effectively when the daughters have newborns.
The organic grandmother has come home, and not a minute too soon. We missed you. We felt sad and lonely and old without you, posthumous before our time. Besides, the kids are crying. They need to be fed. Here's your sack and shovel, Nana. Now will you please get back to work?
Taken at face value, the Hadza research is welcome enough, but Hawkes does more than offer data to resuscitate the moribund Williams hypothesis or buff the reputation of menopause. She has grander plans than that. She has ovarios. In her ambitious, speculative, and perfectly plausible scheme, older women invented youth. They made human childhood what it is today: long, dependent, and grandiose. And in inventing childhood, they invented the human race. They created Homo imperialis, a species that can go anywhere and exploit everything. We think of childhood as having evolved for the good of the child, to give the child time to grow its fat, crenelated brain and acquire linguistic, motor, and social polish. Hawkes turns the arrow around and sees childhood as having evolved for the good of adults, as a period of enforced dependency that paradoxically gave parents enormous freedom. Adults wanted dependent kids. They wanted offspring who needed them enough to stick with them until these offspring were on the threshold of adulthood themselves. With dependent, totable children, early humans could pick up and migrate to lands beyond a pongid's wildest dreams. It's as though teenagers have it right after all: Mom may complain about all her sacrifices and burdens, but just try pulling away and the umbilicus will yank you right back. And helping the hand that reins in the cord and rocks the cradle and rules the world is Grandma. Before we could stay young, we had to learn to grow old.
Let's start by dispensing with menopause. From George Williams on down, the adaptationists have depicted menopause as a watershed event in human evolution, a trait that distinguishes us from other female primates. Their ovaries can keep working to the end, the adaptationists claim, while ours are wired to shut down prematurely, giving us time to raise our families. In Hawkes's view, menopause is beside the point. Women don't undergo "premature" reproductive senescence, she says. Our ovaries last as long as the ovaries of our closest primate kin, the chimpanzees, bonobos, and gorillas: about forty-five years. Presumably the mutual progenitor of humans and great apes also had ovaries that lasted about forty-five years. The forty-five-year ovary could represent the ancestral condition, the primordial seedpod of the anthropoid family, one that is not particularly amenable to adjustment or augmentation. There may be
physiological constraints that prevent natural selection from adding much to a woman's reproductive lifespan. For example, we may be too small. The only female mammals that breed past the fifth decade of life are such giants as elephants and finback whales. If you want to carry a lot of eggs, you need a very big basket.
Whatever the constraints, there is nothing precocious about the senescence of our ovaries, Hawkes says. On that score, she agrees with the artifactualists: women go through menopause because women outlive their follicles. But she parts company with the artifactualists in their insistence that old age is a modern invention. To the contrary, old age is old news. Call us Homo maturus. Yes, people used to die young routinely, of infectious diseases, in the jaws of a leopard, or while giving birth to a fat-headed, rear-facing baby. But those who survived illness and accident very likely thrived to a respectable old age. The Bible puts our allotment at three score and ten, and that's not a bad figure, biologically speaking. We're built to last about seventy to eighty years. Add on the overengineering needed to push a sizable number of people toward that mark, and you get a century. Wherever you go, whatever industrialized, agrarian, or nomadic population you consider, you will find that one hundred years is pretty much the upper limit for the human lifespan. "This is the human pattern," Hawkes says, "and there's no reason to think that it wasn't true for our ancestors as well."
What distinguishes women from other primates, then, isn't menopause but the long, robust life that women can lead after menopause. A chimpanzee at age forty-five or fifty not only has fading ovaries, she is fading globally. All her organs are faltering, and she is close to death. No matter that she has spent her life under the pampering ministrations of an American zoo, with the best medical care and all the bananas she can peel, a female chimpanzee will still be, at fifty, a decrepit animal. She will be the equivalent not of a menopausal woman but of a centenarian, blowing out the birthday candles to the cheers of Willard Scott.
So while natural selection may have been hamstrung by ovarian physiology, unable to augment a woman's follicular capacity beyond the standard primate model, it has flexed its muscles rather floridly on a woman's lifespan. And now we must emphasize the her-ness of human longevity. Let us return to the role of grandmother, and let us gloat. Yes, any wizened elder can, as Jared Diamond suggests, serve as memoirist, botanist, and toxicologist to the clan. But is a good hippocampus worth enough to account for the ascent of the centenarian? Not likely. Life is lived by the day, and most days aren't Christmas. Just as hunting is an irregular occupation, so is playing sage. We need food every day. We need women every day, day after day after year after decade after menopause. Let's build them to last.
By the new and expanded edition of the grandmother hypothesis, the rudiments of human longevity, and of human global domination, can be found in a ritual we take for granted: the family meal. A chimpanzee mother nurses her infant for four or five years. That's a long time, but afterward, there are no more free lunches at Mother's Café. The weaned apeling is expected to fend almost entirely for itself—to find, pick, and eat its own food. On occasion its mother or another older chimpanzee will share foraged goods with the juvenile, particularly if the food is hard for young fingers to manage. But the offered item is a treat, a banana split if you will, and the young chimpanzee knows better than to expect routine handouts.
In food-sharing, though, lies a kernel of possibility. Chimpanzees and other social primates are restricted in their range. They must stay in an area where all members of the group can find enough to eat, and that includes the weaned young. The available resources must be accessible to even the fumbling hands and undeveloped strength of preadolescent animals. If the troop decided to migrate to an area where food was scarce and required adult skills to extract, the younger animals would soon die of malnourishment.
Unless, that is, the adults started sharing food with their weaned offspring on a regular basis. Adults means mothers. Among nearly all species of primates, fathers have little to do with their offspring and probably don't know quite who they are anyway. The males are busy with other things, like hunting. The mother must be the one to give to her children what they can no longer gather for themselves. And that's fine, and she will, but then comes a hitch. She gets pregnant again. She must breastfeed. Lactation is costly. She must eat more than ever. She can't provision the older children and nurse at the same time. Who's she going to call? We know the answer. Her mother. Her auntie. Her cousin Certain Age. Now the chance arises for the occasional robust older female to make a difference to her family's welfare. An aging chimpanzee has nothing to do in a society where the young are autonomous, so she might as well die—right, Mother Nature, you beloved, cavalier, monomaniacal bitch? By contrast, in a setting where provisioning weaned children is essential, Grandmother too becomes essential. The stalwart older female succeeds in keeping her kin alive. The moribund older female does not. Selection favors robustness after menopause, and the human lifespan begins exceeding the primate norm like a pair of outstretched arms, strong and sweet and there to hold you.
Now, with Grandma's help, early humans are free. They can go where other primates, and possibly competing hominids, cannot. They can invade adults-only habitats, where they must dig to unearth tubers and cook many food items to make them edible. (Tubers, incidentally, are fairly rich in protein and calories, and they compose a large part of the diet among many traditional human cultures but are only rarely eaten by great apes.) Mothers can provision their progeny much of the time, but when they give birth they know they'll have help. An elder relative can assume responsibility for weaned children. In fact, with a grandmother's help, a mother can get that new baby off her breast sooner than she might otherwise. Chimpanzees breastfeed for four to five years, the length of time required for the young to reach self-sufficiency. But if a child does not need to be autonomous before leaving the teat, why keep suckling? Even in traditional societies where Similac is unknown and breastfeeding expected, women nurse for an average of only 2.8 years, less time than for other higher primates. Shortened lactation means greater fecundity, and indeed women in traditional cultures have more offspring with their primate ovaries than chimpanzees or gorillas do. The intervals between children are comparatively briefer. More grandchildren enhance the genetic fitness of the senior female. Through food-sharing, then, an older woman becomes a genetic czarina, dynastic in her reach.
As Grandmother grows stronger, children get weaker. It is a developmental rule of thumb that the greater an animal's lifespan, the later the onset of its sexual maturation; if a body is to endure, it must be built with care. Hence the genetic changes that foster life past menopause end up keeping children small and prepubescent comparatively longer. On all fronts, then, children are being infantilized. They are dragged into habitats where meals are beyond a juvenile's means, and then their genes delay their coming of age. Not to despair; instead, gild the cage. The lengthening of childhood opens a window of opportunity for cerebral experimentation. The brain has time to ripen, its synapses to lace and interdigitate and loop back lazily to do it again. For the first two or three years of life, a human child is not that different from a chimpanzee. Both creatures are astonishingly clever and curious, passionate students of life. But within short order the chimpanzee must drop out of school and work for a living, whereas the child—let's be predictable and call her a girl—remains in most cultures in the luxury of the nanny state. The child has all those postmammary years when she is still getting fed and thus can devote her energies to her intellectual and social education. In fact, she is well advised to do so, because even as extended dependency offers opportunity, it poses risks. The young chimpanzee can feed itself. The child cannot. An adult, unlike a fig tree, is not particularly responsive to being shaken or plucked, but instead must be ever so subtly fleeced. That means the child must learn the trade of enchantment: the strategic smile, the well-timed whimper, the feckless eye-bat. She must become a symbiotic parasite, an organism that t
akes and takes and depletes, as a parasite does, but that conveys to its host a sense of reciprocity, of being pleasant, worthy, useful; and that's a hard behavioral feat to manage, requiring a flow chart of routines and subroutines. Another whetstone to a young wit is the nattering chorus known as her sisters and brothers. Mother is fertile. She's having many children. She's weaning them young, and they're loitering at home. All those children are dependent on their elders, and all must beguile and connive to be noticed. Adults may like you soft, but your siblings whittle you sharp. No wonder children are so desperate to grow up: Kinder Garten is infested with snakes.
To review our story: Early humans took a preexisting primate hobby, food-sharing, and professionalized it. By shouldering the burden of feeding children, adults freed themselves to infiltrate whole new lands. But they couldn't have moved without Grandmother's help. Young women needed older women. Robustness after menopause became the rule, as did its corollary, delayed puberty. With Grandma in stride and children in tow, no land was too bleak, no tuber too deep, to dampen humanity's imperial zeal. The more hostile the terrain, the greater the dependency of child on elder. Peter Pan set down roots. Childhood expanded. And with world enough and time, the conditions converged for another revolutionary expansion—of intelligence. Our minds hurtled outward in all directions. We became absurdly creative, Homo artifactus, intolerant of bare cave walls and naked clay pots. We built better tools, better spears, better mastodon traps. The earth that we were fast overrunning was no longer enough, and we laid claim to the heavens, peopling the terrible, silent dome above us with an exuberant divinarium of advisers, legislators, coaches, and entertainers. We lived so long and so self-consciously that we assumed we must live forever, and we buried our dead with enough talismans and spare change for eternity.
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