Women may be the one group that grows more radical with age.
—Gloria Steinem,
Outrageous Acts and Everyday Rebellions, 1983
I am at the end of my research, and I’ve reached Bedlam.
I’m only visiting—I want to better understand the experiences through history of women going through menopause—but this place makes me uneasy nonetheless. Bethlem Royal Hospital is one of the oldest psychiatric institutions in the country. It has shifted sites around London three times since it was established in 1247. Along the way it acquired such a shocking reputation that its very name, shortened to Bedlam, became synonymous with chaos and uproar. Things got so bad in the nineteenth century that the government carried out inquiries into patient abuse, which forced reforms of the hospital.
An article by one doctor in the British Medical Journal in 1912 states that one in twelve of the women being admitted to insane asylums and hospitals like these across the country at that time were postmenopausal. In private institutions, where the wealthier tended to go, they were one in ten. The hormonal and physical changes associated with menopause, as well as the shift it marked in their life and status as mothers, had impacts on the mental health of many older women. Some cases were documented with medical fascination. One doctor described a forty-nine-year-old woman who believes she’s decaying. She eventually commits suicide. Another, age fifty, complains that she’s no longer a human being, with no stomach, heart, or lungs. A forty-six-year-old wife, meanwhile, develops the habit of stripping naked and demanding sex.
This was a time when menopause was grossly misunderstood. Fairy tales painted women at the end of their childbearing years as useless, crazy old crones. They lived in shoes with too many children or killed innocents in gingerbread houses. Farther back in history, they had been treated as witches more literally. At the Salem witch trials in Massachusetts in 1692, sixteen accused women were executed or died as a result of their incarceration, and from what we know, at least thirteen of them were menopausal.
With little understood about menopause and the mental pressures facing older women, people in the nineteenth century tried out all sorts of disastrous cures for its symptoms. One was bloodletting, to get rid of what was believed to be unspent menstrual blood. Sometimes they were given drugs like opium or morphine. In the worst cases, women had their ovaries surgically removed. Meanwhile those who ended up in asylums like Bedlam may have found themselves in the care of strict, fatherly male doctors, bizarrely advising them to drink less alcohol, take hot baths, and wear flannel underwear. One doctor at the time even suggested that menopausal women retreat to a quieter life and withdraw from the outside world, reflecting the attitude that they should be neither seen nor heard.
Life in the asylum wasn’t easy. A woman arriving at Bedlam between 1676 and 1815 would have been welcomed by two imposing stone statues flanking the entrance. They represented the two categories into which most mental patients were thought to fall. The first figure was Raving, desperately struggling against hospital chains, his face contorted with agony. The second, Melancholy, was unrestrained but disturbingly unengaged, as though the outside world had lost all meaning. Of the women admitted to Bethlem Hospital for menopause-associated mental illness, only up to half recovered, according to data in 1912.
Thankfully, the bad days of Bedlam are over. In its current incarnation on a picturesque country house estate in southeast London, Bethlem Hospital is a peaceful place. There’s a collection of small, low wards, each in a separate building, nestled in hundreds of acres of soft greenery. Raving and Melancholy now live in the reception of a small, sunlit museum inside the grounds, where they are brought to life upstairs in the histories of real people. On the wall I find two nineteenth-century photographs, both of older women. One is suffering from chronic mania, her face faintly twisted as she grips a lifelike doll dressed in long white robes. The other, the caption says, suffers from melancholia. She looks as though she’s reflecting on her life, with a pained, faraway look in her eyes.
If fertility represented youth and health, society assumed, then infertility was exactly the opposite. It wiped out the entire point of being female. It turned a woman into something else. And this was reflected in the ways older women were treated, especially by science and the medical profession.
“Estrogen-starved women.”
In 1966 a sensational new health book was published in the United States, promising women that they had nothing to fear from growing old, because science could make them young again. It became an instant hit, selling a hundred thousand copies in just seven months. Its title was as seductive as its contents: Feminine Forever.
According to the author, New York gynecologist Robert Wilson, the answer to women’s (and husbands’) prayers came in the shape of sex hormones. With a youth-restoring blend of hormones including estrogen, he claimed, a woman’s “breasts and genital organs will not shrivel. She will be much more pleasant to live with and will not become dull and unattractive.” They couldn’t reverse infertility, but hormones could at least swat away the hot flashes and mood swings that damaged some postmenopausal women’s lives.
It sounded too good to be true. It wasn’t—at least not entirely. Wilson wasn’t a total quack. With the dawn of endocrinology in the early twentieth century, scientists had finally got a grip on what was actually happening during menopause. The biological mechanism turned out to be quite simple. Every month or so, ball-shaped pockets called follicles grow inside a woman’s ovaries. They release the eggs that are needed to make babies and secrete estrogen and progesterone. Girls are usually born with somewhere between a million and two million follicles, although most of these are gone by the time they hit puberty. Over decades, all the follicles eventually disappear, and it’s their loss that spells the start of menopause. This means no more baby-making eggs and also a drop in hormone levels.
The loss of estrogen in particular is what prompts the symptoms we usually associate with menopause, such as hot flashes, a change in sex drive, mood swings, and weight gain. Hormonal changes before the start of menopause usually begin around age forty-five, with menopause itself starting on average between fifty and fifty-two. It has been estimated that around 5 percent of women experience menopause early, before they’re forty-five. By giving a menopausal woman extra hormones, as Robert Wilson advocated, some symptoms could be alleviated.
Indeed, hormone treatment had already been around for decades before his book was published. In the 1930s a small number of doctors and pharmaceutical companies had begun to reframe menopause as a disease of deficiency, like not having enough vitamins. In some parts of the world, it was no longer seen as a normal, natural part of aging. Within a few decades, it became almost routine for women to take estrogen pills or injections when they reached menopausal age.
According to Saffron Whitehead, emeritus professor of endocrinology at St George’s, University of London, treatments boomed in the 1950s and 1960s. After the Second World War, women who had worked as part of the war effort in Europe were instead encouraged to be housewives, and the idea was that hormone therapy “would keep women sexy and at home,” she explains. Ads for Estinyl hormone tablets from 1952, for instance, feature beautiful, smiling women, their faces floating serenely in a sea of flowers.
Robert Wilson chose to send his own message with a sledgehammer rather than with flowers. He argued that menopause should be recognized as a “serious, painful and often crippling disease,” turning its sufferers into what he disdainfully described as “castrates.” Anne Fausto-Sterling, professor of biology and gender studies at Brown University, who has written about his work, describes his disparaging depictions of “estrogen-starved women.” They are portrayed as existing rather than living, she says. Pictures that he includes in one of his published papers show elderly women walking along in public dressed in black and hunched over. “They pass unnoticed and, in turn, notice little,” he warns his readers.
By the 1960s the hormone treatment wagon had turned into a juggernaut. After Feminine Forever came out in the United States, British journalist Wendy Cooper saw similar success in the United Kingdom in 1975 with her book No Change: Biological Revolution for Women. “She said it was the best thing that had ever happened to her,” recalls Saffron Whitehead. “Everyone, because of this publicity and how young it kept you, would take it.”
Of course, no magic cure ever turns out to be as magic as it first appears. After Robert Wilson died, a scandal in 1981 revealed that his pockets had been lined all along by pharmaceutical companies who were trying to sell more hormone replacement drugs. His best-selling book Feminine Forever had been bankrolled by Wyeth Ayerst, one of the therapy’s biggest manufacturers.
More worryingly for the many women who had been convinced of the transformative power of hormones, researchers discovered that there might be a dangerous link between estrogen replacement therapy and cancer of the lining of the womb. In the early 1990s large studies showed that hormone treatment mixing estrogen and progesterone increased breast cancer risks. And by 2002, another important study confirmed that estrogen and progesterone really weren’t the panaceas they seemed. Hormone replacement therapy, while changing the lives of many women for the better, also increased the risk of heart attacks and strokes.
Prescriptions plummeted and women were advised to take the drugs only for serious menopausal symptoms. Hormone treatment remains a much-welcome boon to many women who take it, but doctors today tend to prescribe it for no longer than two to four years, says Saffron Whitehead. She herself took hormone therapy for fewer than three years. “We’re now on the fence about it,” she says, adding that scientists are still analyzing data to get a clearer grip on how safe it is.
The saga has a both a good and a bad ending. The medical drama surrounding hormone replacement therapy certainly caused uncertainty and panic, and risked lives. But it at least shone a much-needed light on the health of older women. Researchers have dedicated more time to picking apart what the symptoms of menopause really are and to better treating the other problems, including psychological illnesses, associated with old age. A few scientists are even working on solutions to help women of menopausal age get pregnant or delay the onset of infertility.
At the same time, other scientists have turned their attention to the bigger, broader evolutionary question of why women experience menopause at all. Does it serve a purpose, which has some biological logic to it? Or is it like wrinkling and gray hair—an unavoidable aspect of aging, a disease of deficiency—that mark the body’s inevitable decline? Why then do all women experience it, but some men seem to be able to keep reproducing until they die?
When it happened to my mother, she remained an active, working woman. Menopause didn’t stop her from running a business, teaching yoga, cooking, and babysitting. And her experiences are echoed by people like her the world over. As far as history tells us, it has always been this way. The existence of healthy postmenopausal women poses an enormous dilemma for evolutionary biologists. Why would nature render them infertile when they are still so full of life?
“These old ladies . . . were just dynamos.”
When a phenomenon as important as menopause happens in humans, we almost always find it in other species, too, particularly among our primate relatives, like chimpanzees and the other great apes. But with menopause, that’s not the case. It’s freakishly unusual. In almost every species, females die before they become infertile. Chimpanzees are, like us, fertile for no more than around forty years. The difference is, in the wild they rarely survive beyond this. Elephants live longer but carry on having babies into their sixties. A long postmenopausal life is so rare that, as far as we know, humans share it with only a few distant species, including killer whales, which stop reproducing in their thirties or forties but can survive into their nineties.
The reason for this rarity seems to be that we and all other animals have few physical features that haven’t been pared down by evolution to make them fit their purpose. We are streamlined by nature, having long ago ditched most of what we don’t need and honed what we do. Life span appears to be one of those features. By and large, animals live long enough to have children and maybe see them grow up, and then they die. If you can’t reproduce and your genes are no longer being passed along to another generation, then harsh as it seems, nature generally doesn’t want to know. This logic dictates that nobody should be alive beyond menopausal age. By this ruthless measure, my mother and all postmenopausal women should be dead.
Yet they’re all around us. What’s more, on average, they live even longer than men do, even though men can keep producing sperm well into old age. (Although one study in 2014 did find that semen tends to change after the age of thirty-five, making it slightly less likely a man’s partner will get pregnant after sex. Research published in 2003 also showed that pregnancies from older fathers, especially past the age of fifty-five, are more likely to lead to miscarriage and birth defects.)
Answers to the mystery began with a brief observation made back in 1957 by George Williams, a biologist who was one of the most important evolutionary scientists of the twentieth century and at that time working at Michigan State University. The exact question he was pondering was why women lose the ability to have babies in middle age so abruptly when other parts of aging happen more gradually. He proposed, briefly and without much elaboration, that menopause may have emerged to protect older women from the risks linked to childbirth, keeping them alive long enough to look after the children they already had.
Until fairly recently, having babies was a huge killer of women. In the nineteenth century the number who died from or during childbirth in England and Wales hovered between four and seven for every thousand births, and this didn’t fall significantly until after the Second World War. Having babies into old age would have multiplied the risks for both mothers and their children. “It is improper to regard menopause as a part of the aging syndrome,” concluded Williams. His kernel of an idea came to be known as the “grandmother hypothesis.”
To parents whose own parents are still alive, the grandmother hypothesis makes instinctive sense. For me, sitting at my desk today is a benefit made possible by my mother-in-law. She’s busy taking care of my baby son, leaving me free to do other work or have more babies. And she isn’t alone. Grandmothers (and it has to be said, a few grandfathers, too, these days) are a common sight on the streets where I live in London, pushing buggies in the middle of the morning and carting beloved spawn of spawn back from schools and nurseries in the afternoon. It’s a trend that we nowadays associate with busy working parents and the high cost of child care, but it has far longer roots. Extended families, in which children live with their grandparents, were until recently a common feature around the world. In Africa and Asia, they still are. Research by the US-based organization Child Trends found in 2013 that at least 40 percent of children in Asia live with extended family as well as their parents. This, in essence, could have been the kind of crucible in which the grandmother hypothesis operated.
The focus on grandmothering also casts menopause in a new light, suggesting that it isn’t some biological blip or routine curse of old age, but that it’s there for a distinct evolutionary purpose: to allow women to safely continue caring for their children as they grow older and perhaps also be there for their grandchildren. The old image of the useless crone is replaced by a useful woman. Rather than being a burden on society, retreating into a quieter life, she is front and center. She is propping up her family.
For the sixty years since Williams first shared this thought, researchers have been searching for the evidence to prove it.
“I was just trying to understand what the men were doing,” says Kristen Hawkes, professor of anthropology at the University of Utah. She’s the world’s leading researcher on the grandmother hypothesis, and its strongest advocate.
Hawkes spent the 1980s doing fieldwork with the Aché, nomadic hunter-gatherers in Eastern Paraguay. And she soon realized, like anthropologists before her, that men weren’t providing all the food for their families. Hunting by men alone simply didn’t put enough on the table for women and children to survive. “The things that they were foraging for were the things that went around to everybody. So the fraction that went to their wife and kids was no different from what everybody else got,” she tells me. Meat from a hunt not only had to be divided among many but was also sporadic. Long periods of time could go without a kill.
Trying to uncover more clues about how mothers and babies were surviving, Hawkes went to study Hadza hunter-gatherers in Tanzania. The Hadza are particularly special to anthropologists because they arguably live a life as close to how humans lived before agriculture as anyone is likely to find today. A large portion of the Hadza don’t tend crops or herd animals, and they live south of the Serengeti in a region not far from where fossils have been found of some of our very earliest ancestors. “That was paramount for me going to the Hadza,” she explains.
And it was there that she saw hardworking grandmothers.
“There they were, right in front of us. These old ladies who were just dynamos.” It’s impossible to hear Hawkes talk about her fieldwork and not get carried away by her excitement. Her voice shifts a gear and, to this day, she sounds genuinely surprised by what she found all those decades ago. There was a division of labor between childbearing women and grandmothers, with active older women foraging for food alongside everyone else.
Hawkes discovered that the Hadza grandmothers and other senior women, including aunts, helped daughters raise more and healthier children. They were vital to reproduction even if they weren’t themselves having babies. Grandmothers, she suggested, were also the reason women were able to have shorter intervals between babies. They stepped in to help before other children became independent. Her landmark scientific paper on the subject, published with her colleagues in 1989, was titled “Hardworking Hadza Grandmothers.” More work by Hawkes and her team has since revealed just how industrious they are. Women in their sixties and seventies are described as working long hours in all seasons, bringing back as much food or even more than younger women in their families.
Other anthropologists have seen similar things. Adrienne Zihlman, who helped develop the idea of woman the gatherer, recounts a particularly vivid example for me, which she read in the New Yorker in 1990. It comes from the writer Elizabeth Marshall Thomas, who lived with nomadic hunter-gatherers in the Kalahari in southern Africa. Thomas describes a group of people who fell ill during an epidemic. One young widow and her two children were too sick to leave with the group when it decided to shift camp in search of more food. “But her mother was there,” she writes. “This small, rather elderly woman took her daughter on her back, her infant grandchild in a sling across her chest, and her four year old grandchild on her hip. She carried them thirty-five miles, to her people’s new camp.” The superhuman efforts of this grandmother meant her daughter and two grandchildren recovered from their illness and weren’t left behind.
A common counterargument to the grandmother hypothesis, known as the “extended-longevity” or “life-span–artifact” hypothesis, is that menopause must be a by-product of our increased life expectancy. We don’t have to go back many generations to know that we’re living on average far longer and healthier lives than our ancestors. In the United Kingdom, life expectancy for women has risen from forty-nine years in 1901 to almost eighty-three in 2015. This is expected to go up by another four or so years by 2032. In the United States, female life expectancy was just over eighty-one years in 2015, according to the Centers for Disease Control and Prevention’s National Center for Health Statistics. So the line of reasoning goes that older women become infertile because, were it not for all the good food they eat, sanitation, and modern medicine, they would be dead too early to experience menopause at all.
In reality, life-expectancy data can be misleading. A large chunk of a population’s average life expectancy will often be decided by infant mortality. If more children die, this drives down the average. This in turn means there’s every likelihood some people were long ago achieving ripe old ages, even if most of the people around them had shorter lives. According to the latest findings, it is almost certain that some women would have experienced menopause in our ancient past. The earliest recorded mention is often attributed to Aristotle in the fourth century BC, when he is supposed to have noted that women stopped giving birth around the ages of forty or fifty.
Research comparing the body weights and body sizes of our primate cousins suggests that a small proportion of our early human ancestors could have lived to between sixty-six and seventy-eight years. Most convincing, scientists studying hunter-gatherers the way Kristen Hawkes has done have noticed that between 20 and 40 percent of adult women are postmenopausal. In other words, older women would always have existed.
In her book Mothers and Others, anthropologist Sarah Blaffer Hrdy suggests, “Fewer than half of Pleistocene mothers would be likely to have had a mother alive or living in the same group when they first gave birth.” So not every child would have had a grandmother alive, but many would have. Grandmothers are the “ideal allomothers,” she adds. “Experienced in child care, sensitive to infant cues, adept at local subsistence tasks, undistracted by babies of their own or even the possibility of having them, and (like old men as well) repositories of useful knowledge, postmenopausal females are also unusually altruistic.”
Hard data, too, have backed up Hawkes’s findings. Studies in Gambia have found that the presence of a grandmother increases a child’s chance of survival. Similar results have been found in historical data from Japan and Germany. One study of three thousand Finnish and Canadian women from the eighteenth and nineteenth centuries found that women had two extra grandchildren for every ten years they survived beyond menopause.
In 2011 evolutionary demographer Rebecca Sear and biomedical scientist David Coall pulled together research from across the world to find out who, other than mothers, has the greatest impact on child survival. They concluded in their paper, published in Population and Development Review, that maternal grandmothers are consistently among the most reliable helpers. “In more than two-thirds of cases her presence improved child survival rates. Paternal grandmothers were also often associated with positive survival outcomes, though somewhat less consistently: in just over half of cases they improved child survival,” they note.
“Very few species have a prolonged period of their life span when they no longer reproduce,” says Darren Croft, a psychologist who studies animal behavior at the University of Exeter in the United Kingdom. Croft has a particular interest in resident killer whales—orcas—one of a few species of whale in which females are known to stop having babies and yet live for many decades afterward, sometimes into their nineties. The males die far younger, in their thirties or forties.
His explanation for this, outlined in a paper published by him and his team in the journal Science in 2012, lies in the power of the enormously tight bond between whale mothers and their sons. “Female killer whales act as lifelong carers for their own offspring, particularly their adult sons,” he explains. A mother killer whale with a son focuses her efforts on him throughout her life. Indeed, such is the connection between them that data have shown that when a mother killer whale dies, her son is more likely to die far younger. Incidentally, this is just a son thing. The link between the life spans of mothers and daughters is weaker.
Croft carried out further research with colleagues at Exeter University, York University, and the Center for Whale Research in the United States, published in Current Biology in 2015, also looking at resident killer whales in the northern Pacific. Watching the whales led them to believe that it’s the wisdom gathered over their lifetimes that makes the older females so invaluable. “They are more likely than the males to lead a group of orcas, especially in times of short food supply,” says Croft. “For killer whales, what’s really crucial is when and where salmon is going to be,” and the older females seem to have this knowledge.
Croft believes that research like his into menopausal whales, unusual though they are, could provide an extra piece of the human menopause puzzle. If this can happen in the wild to another species, then it could have happened to us. “Following old females isn’t unique,” he adds. Elephants, too, have matriarchs who seem to have special information about threats from predators.
Since the grandmother hypothesis has emerged, other theories have added to it. In 2007 Barry Kuhle, in the psychology department at Scranton University, proposed that fathers (more specifically, absent fathers) might also have helped in the evolution of menopause. His idea is that men become less involved parents as mothers get older, partly because they die sooner but also because they are more likely to leave their partners. This supports the grandmother hypothesis, again, because it makes what grandmothers do even more vital. “I simply added an additional factor,” says Kuhle.
Others have added that grandmothers aren’t necessarily heartwarming, selfless babysitters living in harmonious families. Research published in the journal Ecology Letters in 2012 has indicated that what forces some women into caring for their grandchildren is intergenerational conflict rather than the failure to have babies of their own. Evolutionary biologist Virpi Lummaa and her colleagues studied parish-record data in Finland and found that infant survival was drastically reduced when daughters-in-law and mothersin-law had babies at the same time, if there weren’t enough resources for all the children. If a mother-in-law cares for her grandchildren, she benefits because she is genetically related to them. There’s no such benefit the other way round for the daughters-in-law, says Lummaa. Grandmothers are genetically related to their grandchildren, whereas daughters-in-law are not genetically related to their sisters- and brothers-in-law. Grandmothering, then, is just a canny choice when resources are scarce.
“Men, young and old, prefer younger women.”
The grandmother hypothesis hasn’t gone unchallenged.
At least a dozen competing ideas have come along over the years, each with its own drawbacks and merits. They include the follicular depletion hypothesis, which, like the extended longevity hypothesis, says that women nowadays outlive their eggs. The problem with this is that you might then expect women with more children to go through menopause later, because they’re not menstruating while pregnant. They don’t. Another hypothesis focuses on reproductive cost, saying that baby making takes such a large physical toll on a woman’s body that menopause evolved to protect her from further damage. But if this were true, we might expect to see women with more children experiencing menopause earlier, and we don’t. Another, the senescence hypothesis, offers up the possibility that menopause is just a natural feature of aging, like wrinkles or loss of hearing. And while other side effects of old age may happen gradually, including male infertility, female fertility just happens to end more abruptly for physical reasons.
In 2010 evolutionary biologist Friederike Kachel and a team of researchers at the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, decided to run a test to see if the grandmother hypothesis really is the best explanation for menopause among these alternatives. They ran computer simulations of how humans could have evolved with women living longer after menopause. To the surprise of anthropologist Kristen Hawkes and her team, who by now had amassed many years of evidence in their favor, Kachel’s group found that while helpful grandmothers certainly did raise the survival rates of their grandkids, this effect didn’t appear to be enough to account for why women now live so long.
In 2012, rescuing the hypothesis from news reports that were already questioning it, Hawkes’s team published the results of their own computer simulation, which showed that slowly increasing the proportion of particularly long-lived grandmothers in a population, from 1 percent to 43 percent over the course of thousands of years, could indeed drive up everyone’s life span. She and her colleagues believe that part of the problem with the German mathematical model may have been that it was run for just ten thousand years, when in fact the long sweep of human evolution means that the effects could have taken much longer to appear. They also argue that the model hadn’t accounted for possible costs for men in living longer, such as having to compete with the same number of fertile men for a proportionally smaller pool of fertile women.
Then, in 2014, Hawkes and colleagues at the University of Utah and at the University of Sydney, Australia, plugged their numbers into another mathematical model. In this one, they assumed that at some point in human history we all had similar life spans to our primate cousins, and that, like them, women died before menopause could kick in. The model then slowly feeds in a small number of women with genetic mutations that mean they live longer than everyone else. The mutation spreads, and eventually, very gradually, everyone is living longer.
“When you add helpful grandmothering, at the beginning, almost nobody is living past their fertility,” explains Hawkes. “And yet just those few, those few who are still around at the end of their fertility, that’s enough for selection to begin to shift the life history from an apelike one to a humanlike one. We end up with something that looks like just what we see in modern hunter-gatherers.” All it would have taken in those early days of human evolutionary history was a few good grandmothers.
Not everyone accepts this.
“Let’s assume mating is not random,” evolutionary biologist Rama Singh tells me over the phone from McMaster University in Canada. It sounds as though he’s smiling, aware of just how provocative his comments are going to be.
As both of us know, his is the most controversial countertheory to the grandmother hypothesis. “We know that men, young and old, prefer younger women. So in the presence of younger women, older women will not be mating as much,” he explains. If they aren’t having sex, his argument goes, they don’t need to be able to reproduce. In summary, older women become infertile because men don’t find them attractive. One reporter has described this account as putting the “men” in “menopause.”
In 2013 Singh, along with two colleagues at McMaster, Richard Morton and Jonathon Stone, published the idea in the journal PLOS Computational Biology. It was the kind of paper that instantly attracted worldwide news coverage and a barrage of correspondence. “A lot of women wrote bad letters to us,” admits Singh. “They thought we were giving men more say in evolution.” One sarcastically demanded to know just how much sex she would need to have as an older woman to avoid menopause.
“Whether you believe it or not, just look around society today. The science is cut and dried,” he responds, when I ask him about the criticism. “The truth is, nature doesn’t care about sympathy or feeling.”
Many, however, have challenged his view of nature. Indeed, Singh, Morton, and Stone’s hypothesis has been mocked in scientific circles. “It makes very little sense. Chimps actually prefer older females as their mates,” Virpi Lummaa, at the University of Sheffield, tells me. Another prominent researcher in the field, Rebecca Sear, at the London School of Hygiene and Tropical Medicine, agrees. “It’s a stupid argument and it was trashed when it came out. It’s a circular explanation. The reason men don’t prefer postmenopausal women is that they’re postmenopausal and they can’t get pregnant, not the other way round.” Even so, Singh and his colleagues have stuck to their guns, unapologetically.
Their idea isn’t entirely new. The inspiration for it stems back to 2000 when anthropologist Frank Marlowe, then working at Harvard University, published a provocative explanation for menopause known as the “patriarch hypothesis.” Like the name suggests, the patriarch hypothesis is about powerful men, specifically, men powerful enough to be able to have sex with younger, fertile women even as they get old. “Once males become capable of maintaining high status and reproductive access beyond their peak physical condition, selection favoured the extension of maximum life span in males,” Marlowe explains in his paper, which was published in the journal Human Nature. Even a few high-status old men spreading their seed would have been enough to produce a difference in how long humans lived, he argues.
Since the genes associated with increased life span happen not to be on the Y chromosome, which is shared only through the male line, this means that women would also have inherited the same trait for longer life. In other words, because their fathers survive for as long as they do, daughters are dragged along for the ride. “Like nipples,” explains Michael Gurven, an evolutionary anthropologist at the University of California, Santa Barbara. Men have nipples because women have nipples, even though they don’t need them. Similarly, goes the patriarch hypothesis, women enjoy long life spans even though they don’t need them, because men do.
When they explored the patriarch hypothesis years later, Singh, Morton, and Stone believed that Frank Marlowe’s line of thinking didn’t fully explain how menopause could have emerged. Running computer models to simulate how humans might have evolved in our early history, they found that adding a few genetic mutations for infertility into the population didn’t have much of an effect on everyone’s fertility as time wore on. These mutations just died out. “Fertility and survival remained high into old age. There was no menopause,” they said. But when they added the critical element of older men preferring to have sex with younger women into their simulations, female menopause did pop up.
It was evidence, they claimed, that the patriarch hypothesis, slightly tweaked, could explain menopause in women. Grandmothers may be hardworking, but in the end it just comes down to sexual attractiveness.
Like Kristen Hawkes, Frank Marlowe had also studied Hadza hunter-gatherers at close quarters for many years. The difference was that he came up with a different explanation for human longevity and menopause. So how did two distinguished researchers studying exactly the same group of people come to two such conflicting theories?
Anthropologist Alyssa Crittenden at the University of Nevada, Las Vegas, who has worked closely with Frank Marlowe, believes part of the reason may be because he and Hawkes were with the Hadza at different times, with an interval between them of almost two decades. These communities, as fragile as they are as they interact with the rest of the world, may have changed how they lived even in that short time. The same way, for example, as the women of the Nanadukan Agta in the Philippines began to abandon hunting.
But there are other explanations. “Part of it may lie in the sex of the researcher,” Crittenden admits. “Science is supposed to be objective,” but it’s possible that their sex affected how they collected their data, she adds.
Hawkes and Marlowe now have their own scientific camps, each with their own versions of the past, one favoring powerful old men and the other favoring grandmothers. “The one I’m betting on really does make grandmothering the key to this special characteristic of our longevity,” states Hawkes. For the patriarch hypothesis to work, she explains, there would have to be at least a few old men alive in the beginning to make these patriarchies happen in the first place, and the fact that our primate cousins don’t have any elderly chimps or apes among them raises the question of where on earth these older men might have come from in large enough numbers. “The problem with his patriarch hypothesis is he has to somehow get to the place he wants to start,” she tells me.
By the time I call Marlowe in 2015 he has Alzheimer’s disease and isn’t available for an interview. Alyssa Crittenden tells me that although she still very much respects his research, his scientific article on patriarchs hasn’t stood the test of time as well as some of his other work. It has been cited far less by other researchers than Hawkes’s papers on the grandmother hypothesis, for example.
Others, however, continue to disagree. When I ask evolutionary anthropologist Michael Gurven about the grandmother hypothesis, he is skeptical of it. In 2007 Gurven, together with Stanford University biology professor Shripad Tuljapurkar and Cedric Puleston, then a doctoral candidate at Stanford, published a paper titled “Why Men Matter: Mating Patterns Drive Evolution of Human Lifespan.” In it they argue, along the lines of Frank Marlowe’s patriarch hypothesis, that the general pattern for husbands to be older than their wives, along with a small number of high-status older men managing to mate with younger women, could partly account for why humans live so long.
Their view is that even if the grandmother hypothesis was true, men must have had a role to play as well. “You can’t correctly estimate the force of selection if you leave men out of the picture,” Puleston told a reporter from the Stanford News Service when their paper came out. “As a man myself, it’s gratifying to know that men do matter.”
Gurven these days takes the middle ground between men and women by suggesting that grandparents of both genders, not just the female ones, are responsible for our long life spans. He doesn’t believe that women alone could account for such an important feature of human evolution. This two-sex model claims that it isn’t only babysitting or food production that makes older people useful. Passing down knowledge from generation to generation could be one benefit, according to Gurven. Another could be in mediating conflict. Big-brained and complicated as humans are, skill usually comes with age. This wisdom sharing is something that both men and women could have played a role in through history.
The problem for everyone in this field is that the data are both scarce and messy. We can’t know for sure how people lived many millennia ago. The Hadza, remarkable a window on the past though they might be, are nevertheless a small and dusty one. And evidence from other hunter-gatherer communities around the world is even more sketchy. This leaves room for speculation. Gurven is on the softer end of opposition to the grandmother hypothesis. Marlowe, Morton, Stone, and Singh have been on the harder end. But the trend here isn’t difficult to spot: countertheories to the grandmother hypothesis appear to come mainly from men.
Gurven laughs when I ask him if there might even be some bias at work in his field of research. “You mean humans studying humans have bias?” he asks sarcastically. The rainbow of explanations for why humans live as long as they do and what makes older people useful in different societies means that many more things are possible than would have actually happened, he explains. It is this room for uncertainty that makes menopause such a volatile subject. From patriarchs to grandmothers, we may never know for sure who’s right. “If you polled a whole bunch of people and asked them what they believe, would more women choose the grandmother hypothesis and more men the patriarch hypothesis? I wouldn’t be surprised. . . . It’s hard to remain completely unbiased,” Gurven admits.
His opinion is that Morton, Stone, and Singh’s hypothesis about men alone causing menopause is a case of wishful thinking. But he also believes that Kristen Hawkes has fought too hard for the grandmother hypothesis, even neglecting critiques of her evidence. It survives, he says, because it is sexy, not because it is right. “By throwing men under the bus, it seemed to be a radical new idea and people clung to that,” he tells me.
Donna Holmes, an expert on the biology of aging based at the University of Idaho, agrees with Gurven on this point. She tells me that she has clashed with Hawkes over the grandmother hypothesis, and that she’s still not convinced by it. “It was provocative and fresh. It made feminists happy, because it was grandmother friendly and went against the idea that older women are not valuable. It made liberals happy, because they like to think that aging can be ‘natural’ and accomplished without intervention by the evil pharmaceutical industry,” says Holmes. “So it became very fashionable.”
Alyssa Crittenden doesn’t see it this way. “It’s important to highlight the role that Kristen Hawkes played,” she says. Torn by what she sees as compelling arguments both ways, she tells me, “Gun to my head, I choose the grandmother hypothesis.” Over the many years since both hypotheses were originally published, the data have strengthened the grandmother hypothesis more than they have Frank Marlowe’s patriarch hypothesis, she adds. “I’m continually blown away by the economic effort that postmenopausal women expend. . . . I really believe grandmothers have a really special role.”
More than three decades since publishing her original paper on hardworking Hadza grandmothers, Kristen Hawkes maintains that the weight of evidence is on her side. “I had no notion that what old ladies were doing was going to turn out to be so important,” she tells me. “It really highlights the extremely important effects that postfertile females have had on the direction of evolution in our lineage.”
However controversial it might be, her research has helped bring older women into the evolutionary frame. A door has opened to a completely different and more positive way of thinking about aging. And today it sits inside a wider body of work questioning whether menopause should in fact be welcomed rather than feared. As far back as the 1970s American anthropologist Marcha Flint studied communities in Rajasthan in India, where women saw old age very differently. They told her it was a good thing, giving them a new social standing in their communities and more equality with men. Flint described negative American attitudes to menopause, in contrast, as a “syndrome.” When menopause is seen as a curse rather than a blessing, women feel naturally less happy about it and also seem to report more symptoms.
This observation has been more recently supported by others. Researcher Beverley Ayers, when working in the psychology department at King’s College London in 2011, argued that the way the Western medical profession has treated menopausal women has made them believe that menopause has more symptoms than it really does. In an article published in the Psychologist she and her colleagues explain that Western women have reported experiencing “hot flushes, night sweats, irregular and heavy periods, depression, headaches, insomnia, anxiety and weight gain,” while in India, China, and Japan, these symptoms aren’t nearly as common. One explanation might be that women are lumping in the effects of growing older with their experiences of menopause. If science tells them that menopause is a disease, they start feeling as though it is.
The story of menopause is the story of how science has sometimes failed women. But, as the grandmother hypothesis shows, science has provided alternative narratives, too, ones that not only challenge old preconceptions and tired stereotypes but also can be truly empowering. Indeed, Kristen Hawkes’s latest work suggests that hardworking grandmothers may have appeared very early in human development, around two million years ago, meaning they could hold much more than just the key to human longevity. “It may have been helpful grandmothering that allowed the spread of genus Homo out of Africa and into previously unoccupied regions of the temperate and tropical Old World,” she speculates. In her version of the story of us, ancient grandmothers weren’t just powerhouses in their families but vehicles for enormous change as humans migrated across the globe, tens of thousands of years ago. Age was no barrier to exercising their strength.
With the hard work of these women, everything was possible.