by Angela Saini
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 hypothesi
s 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.
AFTERWORD
The feminists had destroyed the old image of woman, but they could not erase the hostility, the prejudice, the discrimination that still remained.
—Betty Friedan, The Feminine Mystique, 1963
A science book on the shelves of the Wellcome Library in Bloomsbury, London, not too far from where I live, caught my eye. There among the rows of academic journals and medical textbooks, tucked away in one corner, was a small volume published in 1952 and titled The Natural Superiority of Women.
“The natural superiority of women is a biological fact, and a socially overlooked piece of knowledge,” wrote the author, a British American anthropologist by the name of Ashley Montagu. This bald statement sounded radical to me when I first read it, but I could only imagine how much more radical it must have sounded back in the 1950s, when women had the vote but not much else. By the time I found his book, I had already pored over many hundreds of pages of scientific literature stretching over two centuries dedicated to the idea that women are somehow inferior to men. This little volume was a rare exception. And it was written by a man. I bought my own secondhand copy.
As I learned later, this wasn’t Montagu’s only controversial piece of work. He was a prolific author who had lectured at Princeton and became something of an intellectual celebrity in the postwar years, appearing on American chat shows. When Hitler was committing atrocities against Jews in Europe, he wrote about the fall
acy of the biological idea of race. In his writings on women, he compared their subjugation to the historic treatment of black people in the United States. He campaigned against genital mutilation long before it was the high-profile issue it is today.
Montagu wasn’t always Montagu. He was born Israel Ehrenberg to Jewish Russian immigrants in 1905 in east London—an upbringing that would have almost certainly made him a victim of anti-Semitism. Maybe that’s why he ended up changing his name. He picked the eighteenth-century writer and feminist Lady Mary Wortley Montagu. She had been known for her travel writing from the Ottoman Empire and for advocating in favor of smallpox inoculation after she saw it being used effectively in Turkey. She was so sure this medical practice would save lives that she had her own children inoculated, long before it became common in England.
I don’t know whether Lady Mary was any more of an inspiration to him beyond her name, but she seems to have been. In the pages of his book, Montagu looks at the biological measures by which we assume women are inferior to men. He uses data to show that, intellectually and physically, women aren’t weak and feeble. And he makes a passionate case for improving the status of women. It’s not always objective. In fact, at moments, he seems a little amused by his own idea. “If I sometimes poke a little lighthearted fun at my own sex, I hope that no man will be humorless enough to think that I am casting aspersions upon him,” he reassures.
But Montagu is also clear that men have everything to gain from embracing change. He calls for flexible working patterns, in which parents can split child care evenly between them so both can enjoy the benefits of raising their kids. He asks husbands not to leave housework to stay-at-home wives, however much they dislike it. “Man is himself a problem in search of a solution,” he writes. “When men understand that the best way to solve their own problem is to help women solve those that men have created for women, they will have taken one of the first significant steps toward its solution. . . . The truth will make men free as well as women.” It’s a message as timely then as it is now.