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Authors: Natalie Angier

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ago, when we were as yet
Homo erectus
. But evidence to prove her proposition is hard to come by. Soft tissues such as ovaries do not leave fossils behind.
The backlash against the organic grandmother began in the 1970s, coincident with attempts by the medical community to promote estrogen replacement therapy for middle-aged women. As doctors became convinced that estrogen is the primary reason that women don't usually have heart attacks until after menopause, they began to question the desirability and "naturalness" of programmed ovarian senility. The grandmother hypothesis posits that women stop ovulating so that they can live longer and tend to their existing young; why, then, would the cessation cut off the primary source of a wondrous hormone that can keep women alive? How silly and self-defeating. Surely the adaptationists must be wrong. Surely menopause was not selected by evolution but is, like gray hair, merely another sign of our decay. And just as gray hair can be dyed or highlighted into the verisimilitude of youth, so the worst side effects of menopause can, and should, be ameliorated with estrogen replacement therapy.
The backlashers brought out the scorpion whips and cat-o'-nine-tails. Paleontologists argued that middle age and old age are themselves quite new. Until a few thousand years ago, they said, almost nobody lived past their early forties. The bones that have been found of early hominids are overwhelmingly the bones of young people. There are few if any postmenopausal women, no merry crones, in the fossil record. It's ridiculous to argue that natural selection has favored the onset of menopause in humans when early humans rarely lived long enough to enjoy hot flashes or Meadian zest. Women, and men, died by the age of forty-five. A woman's eggs will last her until about forty-five. As paleodemographers see it, the fit is pretty snug: a woman has all the eggs she needs to live the life she did when selective forces carved out the rudiments of our fate tens of thousands of years ago. If women today breezily outlast their egg supply and write best-selling books about the experience, fine, bully for them, but we're all artifacts of fortified food, purified water, and Jonas Salk, and evolution has nothing to say about us or our geriatric athleticism.
Nor could anthropologists find support for the adaptive value of menopause among contemporary "primitives." In the 1980s, Kim Hill

 

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and Magdalena Hurtado, of the University of New Mexico, studied the Ache of the eastern Paraguayan forest, another group of hunter-gatherers who must shoulder the burden of prehistory's silence. The anthropologists amassed a large and exacting data set. They observed the help and succor that older Ache women gave to their children and grandchildren. They devised theoretical models comparing the indirect genetic benefits that the grandmothers reaped by devoting themselves to their existing children and grandchildren with the direct genetic benefits that the women would have accrued if they had been able to continue bearing babies past menopause. An adaptation supposedly enhances your reproductive fitness, the ability to throw your lovely and singular genetic garland into tomorrow. If the grandmother hypothesis were valid, then presumably the contributions that the elder Ache women made to the health and survival of their children's children should outweigh the genetic gains of having two or three more children of their own. Alas, the bonus babies won: the anthropologists concluded that the Ache grannies were making surprisingly little difference to the prospects of their grandchildren and that the seniors would be better off from a strictly Darwinian standpoint if they could be mothers past menopause.
Through mathematical simulations, Alan Rogers, of the University of Utah, reached a similar conclusion. In a 1991 paper, he estimated that a woman would have to be a comic-book heroine, Neutron Nana, to make menopause look like an adaptation. Her ministrations to her family would have to double the number of children that
all
her children bore and help keep
all
her grandchildren alive to give premature reproductive senescence an edge over maternity in haghood. Even Demeter, the great goddess of the harvest, couldn't prevent her daughter, Persephone, from going to hell for six months of the year.
I was reared at the knee of the grandmother hypothesis. Even as a girl whose menopause was decades away, I found comfort in the idea that when it happened, it was all part of an optimal design. The thought of it linked me to my mythical ancestors, those dusty, lanky, demimonde women striding across the veldt, their brains expanding with every step. Hence I despaired when, in the 1990s, the facts seemed stacked against it. Many of the scientists I talked to thought it was a charming notion, but probably wrong. "Adaptive menopause is an interesting idea, and I

 

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wish I could believe in it," Steven Austad, a zoologist at the University of Idaho, said to me in mid-1997. "But I just don't see the evidence to support it." And from Alison Galloway, an anthropologist at the University of California in Santa Cruz: "I don't buy the Grandmother Hypothesis. I don't think there's anything beneficial about menopause. I don't think it's been selected for. It's the result of recent expansions in our lifespan. We outlive our follicles." Margie Profet, architect of the menstruation-as-defense theory, told me that it didn't matter, in an evolutionary sense, if postmenopausal women lacked the protection menstruation afforded: women weren't supposed to live past fifty. Jane Brody, my colleague at the
New York Times
and a proponent of hormone replacement therapy, has written that women shouldn't worry about hormone therapy's being unnatural, because a "woman's current life expectancy, on average, of seventy-seven years is not natural either."
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

 

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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 grandchildren. 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

 

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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

 

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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

 

BOOK: Woman: An Intimate Geography
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