©2019 by Kathleen Berger

Why Grandmothers?

The Paradox of Menopause


That question bothered me, too. What are grandmothers for? What is the purpose of life, when menopause makes birth impossible? Grand- mothers are often pushed aside. Instead of pushing back, should I ac- cept that I am a sterile old woman who should quietly disappear?

     As George Williams (a scholar whose insights changed the social sciences for generations) expressed it, “The paradox about human fe- male menopause is that evolutionary theory predicts that there should be no selection for any post-reproductive life-span. The reason is that sterility is—in principle—the selective equivalent of death.”2

     Figuring out this paradox requires understanding human biol- ogy over hundreds of thousands of years. That makes research on the Hadza relevant. In a small region in northern Tanzania, the Hadza cluster into groups of 6 to 139, living as nomadic hunter-gatherers, as did all humans before agriculture required settlement about eleven thousand years ago.3 Social scientists hope that Hadza life patterns reflect inborn human nature.

     Each Hadza group relocates every few weeks when nearby food is depleted. Everyone hunts or gathers. Men hunt at night, using arrows to fell impala, eland, zebra, or giraffe. The researchers reported that one time the hunters returned sorrowful, empty-handed. Fortunately, the women gather the community’s main sustenance, tubers, nuts, and honey, so no one starved.

     Food is shared when needed. After this failed hunt, a nearby Hadza group sent scraps from a dead giraffe. The Hadza consider themselves all one people; individuals move freely from one group to another.

The eight senior women spent more time gathering than did the younger women. Nursing mothers, particularly, foraged less. Newly weaned children gathered almost nothing: they lost or gained weight depending on the grandmothers.

     The basic premise of evolution is that every characteristic of all liv- ing creatures serves survival or reproduction. Peculiarities, such as the peacock’s feathers, the giraffe’s neck, the salmon’s death swim, promote life. Extinction occurs when too few survive to reproduce. That was the fate of 99 percent of all the species that ever lived, including more than a billion kinds of fish and insects, every type of dinosaur, and all of the human species save one—Homo sapiens.

     Our species is unusual, not only for survival but also for prolifera- tion. Homo sapiens multiplied and spread from East Africa to all corners of the earth, the only species to thrive on every continent. Because humans are one species, a Zulu warrior could marry a Siberian woman, and they could have many fine children. Their cultural differences might cause friction, but their biology would not.

     How did Homo sapiens survive, when an estimated five billion larger and smaller species died? Possibilities abound, including digits, diet, language, fire. Might grandmothers be the reason?5 Could midlife menopause—halting motherhood and allowing grandmotherhood—be life sustaining rather than “the selective equivalent of death”?

     Ancient teeth and bones reveal that extinct hominids and other early mammals had few grandparents. Ancient burying grounds for those long-gone species find that almost no one survived past age thirty.6 Suddenly, at about the same time that Homo sapiens first ap- peared, the proportion of grandparents in the population almost tripled. Did grandparents transmit vital knowledge (such as where to dig for tubers and how to survive climate change) that prevented extinction? Does longevity allow transmission of technology, social organization, and values that aid the entire species?

     The possibility that aging women increased survival is buttressed by studies in the animal kingdom. Among Asian elephants, compared to newborns without a grandmother, a newborn with a grandmother nearby is eight times less likely to die young.7 Unlike elephants and humans, most mammal grandmothers are pre-menopausal, busy with new babies because they are young and fertile.

     You might be confused if you have learned that, in past millennia, human life was “solitary, poore, nasty, brutish, and short,”8 with sur- vival until age thirty or so, on the average. However, that average is an arithmetic mean reflecting many dead infants and young children. Our fortunate foremothers who survived infancy, childhood, and childbirth usually reached grandmotherhood, menopause, and then old age. That is dramatically true now; worldwide, the average woman lives three decades after menopause (four decades in Japan).

     Genes sometimes change over time, via selective adaptation if a mutation benefits survival and reproduction. But that has not happened with the genes for menopause at about age fifty and survival for decades beyond that. Those genes have been transmitted from the first women to walk the African soil, long before modern medicine. That fact but- tresses the case that menopause aids species survival. Further evidence comes not only from archeology but also from the Hadza: “Many women live . . . into their 80s,” never seeing a doctor.9

     This aspect of human biology is peculiar. Even with excellent medical care, death comes quickly to virtually all post-reproductive mammals, from aardvarks to zebras. Some other primates experience menopause, but their lives end soon after that.10 Menopause plus lon- gevity is unique to human females, elephants, and two species of whales (Orcinus orca and Globicephala macrorhynchus).

     The more biologists learn about other species, the more bewilder- ing this is. Many creatures die before the next generation is born. The female praying mantis eats the male while he impregnates her, biting off his head before copulation is complete. This aids species survival; his body nourishes the pregnancy. Many fish and insects die after laying eggs, as Charlotte did soon after her triumphant, Wilbur-saving web.

     That is never the case for mammals: until recently, newborns starved without breast milk, which, to begin, requires pregnancy. (Mammals are named for mammary glands that produce milk.) Most primates nurse their babies for years. Not until baby gorillas, baboons, orangutans, or chimpanzees are finally weaned (age four or later for chimps) do the mother’s pheromones broadcast that she is fertile, which alerts every male. In some primate species, receptive females display another come-hither signal: their buttocks turn bright red.

     If female primates are not cycling, gestating, or nursing, they are dying; no male is interested. Human primates are an exception; sexual attraction is disconnected from fertility, and life continues decades af- ter menopause. Why? A clue comes from those two species of whales. Postmenopausal whales help their grown offspring find food and avoid predators: adult whales are more likely to survive if their postmeno- pausal mother is nearby.11

     After Charlotte died and baby spiders began to hatch, Wilbur said, “I shall always treasure her memory. To you, her daughters, I pledge my friendship, forever and ever.”12

I cried when I read that: it is touching that Charlotte died for her children and that her sacrifice is memorialized by her friends, pledging to love her progeny.

     But that is neither my plan nor my fate, unlike virtually every other species and unlike human men. The male example is instructive. Why can men father children in old age? One man holds the record: Ramajit Raghav, from rural India, claimed to father one baby at age ninety-four and a second at age ninety-six. That brought him fame but not hap- piness. His first son disappeared at age two, and his wife (in her early fifties) left with the second at age one.13

     Even if his wife and children had stayed, Ramajit was unlikely to be an active father throughout their childhood. That would be his loss as well as theirs because men who become active caregivers tend to be happier and healthier than other men their age. Hundreds of studies leave no doubt that children benefit from involved fathers and grandfathers. Nonetheless, childbearing stops in midlife for women, not for men.

     The reason is the nature of human mating. Although it is possible for an old man to become a father, men usually stop fathering children when their wives stop bearing children. Humans tend to notice unusual cases, which is why people are aware of men’s midlife divorce, remar- riage, and late fatherhood. But that pattern is relatively rare.

     To be specific, contrary to the impression from headlines, most men marry women only a few years younger than they are, most di-vorces occur in the first five years of marriage, and only one newborn in a hundred has a father older than age fifty.14 These rates have increased in the past decades, but almost all older husbands stay with their post- menopausal wives.

     Indeed, late fatherhood may be destructive, not only because women often choose children over men, as Ramajit’s wife did, but also because advanced paternal age at conception correlates with problems in the fetus and child.15 Rates of autism, particularly, rise when the father is over age forty-five.16

     How might long life after midlife menopause benefit the species? Research led primarily by women (Kristen Hawkes on the Hadza, Sarah Hrdy on allomothering, Rebecca Sear in West Africa, Ruth Mace on cooperative breeding, Jan Beise on Germans and Québécois) developed the grandmother hypothesis.

     Grandmothers are ideal allomothers, or people who care for chil- dren but are not their biological mothers. Young mothers need allo- mothers; raising children alone is arduous. Fathers often help, but not always, and even with two involved parents, childrearing is difficult.

     Throughout the millennia, grandmothers have often been allo- mothers. When older women no longer bear children, they help their grown daughters with pregnancy, birth, and child care, allowing young women to become pregnant again. A new pregnancy soon after giving birth is biologically impossible for other primates; they are infertile un- less their infants die or are old enough to care for themselves.

     Allomothers are essential for Homo sapiens because lengthy brain development (unlike in every other creature) makes human children and adolescents vulnerable to starvation, predators, raging rivers, speeding cars, and many other killers for decades before neurological maturation allows self-preservation. For survival, “each new human being [needed] protectors—people who make sure that the child can thrive, learn, and imagine in spite of being so vulnerable. . . . Those protectors are parents, of course, but they also are grandparents.”17

     Grandmothers kept infants from wandering off into jungles, in much the same way that they now keep children from running into traffic. Historically, childbirth was the leading cause of female death between ages fifteen and thirty-five. It was essential that lactating and loving caregivers be available to nurse and nurture motherless children.

     Over two hundred thousand years, because of grandmother al- lomothering, more offspring were conceived, more newborns survived, more toddlers were protected, and more children became educated adults. Humans multiplied; other primates did not.

     Menopause kept older women from the demands of their own infants. Those ancient, protective, genes and habits have endured. Modern humans still need allomothering.

     I observed that myself. On a crowded subway, I sat in front of a standing young woman, balancing an infant and several packages, pre- cariously grasping a pole. I offered to help, expecting to hold her pack- ages, but she handed me . . . the baby. I sang quietly to the infant as the train hurtled through the tunnel. I should not have been surprised at the mother’s trust: our genetic mandate includes shared child care.

     Human allomothering is in stark contrast to chimpanzee mothers who hide their infants from other chimps, fearing poking fingers and infanticide (a realistic fear; newly dominant males kill newborns).

     Older female humans have always been fiercely protective, as well as caring, not only of their own descendants but also of other infants. This is an inner compulsion, far beyond rational. Seeing, touching, and caring for an infant unlocks a flood of hormones; we care for babies not our own.

     When my pediatrician was examining Bethany, my firstborn, I asked, “Isn’t she one of the cutest, smartest babies you have ever known?” He responded with a twinkle, “Yes, and my patients are cuter and smarter than the patients of other pediatricians.”

     Caregiving fuels allomothering; logic and inheritance are not required. Five of those early-rising Hadza crones were genetic grand- mothers, but the other three were not. They had no grandchildren who needed them, but each dedicated herself to another family. Likewise, in the twenty-first century, children have a host of allomothers: teach- ers, doctors, nurses, babysitters, neighbors, and more. If our early care depended solely on our mothers, most of us would be dead.


     Menopause, long life, and allomothering are factual, but not every scientist accepts the grandmother hypothesis.18 Two other ideas have been proposed:


  1. The good mother hypothesis. Older children need motherly at- tention; good mothers should not be torn between caring for infants and older children.

  2. The resource competition hypothesis. Men can continue their genetic legacy with a new wife and children, but human babies need resources to survive, so they need mothers to provide for them.

Neither of these theories contradicts the grandmother hypothesis. Good grandmothers are good mothers, and resource competition in- creases the need for grandmothers.

Grandmothering: Building Strong Ties with Every Generation, Kathleen Stassen Berger, Rowman & Littlefield, all rights reserved.