Not long after our first child was born, my wife and I contacted my mother in Pakistan to see if she could come and stay with us for a while in Durham, N.C., where I was training to be a cardiologist. We were overjoyed when she agreed. But when she arrived at the airport counter to collect her boarding pass, she learned that her valid visa had been unceremoniously cancelled without any reason given.

That she couldn’t come see her only granddaughter (and help out her parents) was devastating for all of us. But as two recent articles published in Current Biology show, the presence of grandmothers goes far beyond sentimental implications: They may be responsible for the success of the human species.

First, some background:

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Evolutionary biologists have long been struck by two unique features of humans. The first is that we enjoy some of the longest life spans in the animal kingdom. In just the past 200 years, there has been an unprecedented increase in how long we live, not just in the richest countries but also in the poorest. We have moved so far away from our hunter-gatherer ancestors that their life spans are more similar to those of apes and chimpanzees than to modern human beings.

This feature is coupled with another. To a biologist, an organism that cannot reproduce is of little value in evolutionary terms, an unmitigated oddity. So scientists have been puzzled by the long postmenopausal life of human females. From a purely evolutionary perspective, grandmothers can be considered a failure of reproductive fitness: What good is an organism that cannot reproduce and cannot help perpetuate the species?

Yet as newly published studies are confirming, grandmothers may not only help perpetuate the species but also be one of the reasons why humans enjoy long lives to begin with.

Human females were once thought to be the only mammals with a long postreproductive phase of life. Scientists have since identified other mammals, like orca whales, with long postreproductive life spans. It turns out that these two features, humans’ long life spans and women’s long postreproductive lives, might be connected through “the grandmother effect.”

Evolutionary biologists have shown that the very women who were once thought to be an evolutionary aberration may be a key to human longevity. By helping raise their grandchildren, grandmothers in hunter-gatherer (and even more modern) societies allowed their daughters to have more babies. Mathematical simulations have demonstrated that the grandmother effect, first posited in 1966, is an important reason human life spans moved from an apelike pattern to our current one in both modern and more primitive societies.

By relieving a mother of some of her child-raising responsibilities, so the thinking goes, grandmothers make it easier for their daughters to have more children and also make it possible for those children to have longer lives by helping them during the difficult early years of life.

Two new studies, both published in Current Biology, strengthen this notion. An analysis of church birth and death records in Finland for individuals born between 1731 and 1890 showed that having a maternal grandmother between 50 and 75 years of age while a grandchild was 5 years old or younger increased the child’s survival. The effect disappeared for grandmothers older than 75 years of age, possibly because they may not have been be able to help with child rearing. The effect on longevity was seen mostly with maternal grandmothers and not paternal grandmothers.

The second study drills down into this effect, showing that it is not just the existence of a grandmother, but her proximity that matters. The shorter the distance between grandmother and grandchild, the more involved the grandmother can be and the more benefits that accrue to her daughter and grandchildren.

These new studies strengthen the pre-existing case for grandmothers, indicating just how important they might be to the success of our species.

In some ways, though, we are at a crossroads. For centuries, grandmothers have helped their family units grow. Yet more families now live by themselves, without grandparents, than at any time in the past. Over the course of the 20th century, the nuclear family has transformed, with some of the greatest changes coming from geographic dispersion. At the start of the 20th century, only 7 percent of older women lived alone. That peaked at 38 percent in the 1990s and is now at about 32 percent. If this dispersion continues, we could effectively reverse the evolutionary role that grandmothers have played and may lose the benefits we have achieved from this effect.

What must change is not only a greater understanding of the role grandmothers can play but also an increased effort to return to multigenerational family units. Such a movement would help both mothers and grandmothers, particularly as the latter grow older and require care for themselves.

Modern families ought not look just to grandmothers. Grandfathers also need to be part of the equation. Just as fathers have taken on an increasing role in parenting, so should grandfathers.

Children who grow up in multigenerational homes have better high school graduation and college enrollment rates and fewer emotional and behavioral problems than those who don’t. After Barack Obama’s parents divorced, he spent several years living with his grandparents in Hawaii. His upbringing represents a prominent example of grandparents doing a wonderful job helping raise a grandchild, especially when the parents’ situation is complicated.

Even as we think of new ways to enhance the upbringing of our children, we should hold to some old ways and do what we can to prevent a reversal of the grandmother effect that has been so central to the growth of the human species.

Our daughter, Eva, is now 3 years old and my wife and I are still not ready to have another child. Eva takes up everything we have: our love and attention, but also time and our energy. One thing that might change the equation, though, would be if my mom was able to get a visa and come to the U.S.

While our family and others stand at the unexpected intersection of schizophrenic immigration policies and evolutionary biology, and we look for what is best for the future of our children, science would suggest that we should begin by looking to the past.

Haider Warraich, M.D., is a fellow in advanced heart failure and transplantation at Duke University Medical Center and author of the forthcoming “State of the Heart: Exploring the History, Science & Future of Cardiac Disease” (St. Martin’s Press, July 2019). The views expressed in this article are those of the author and do not necessarily reflect those of his employer.

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  • Wow! This article does a great job of illustrating the Rashomon effect. The article discusses a hypothesis that tries to explain why humans have longer lifespans than other mammals. This is not new material, by the way, it merely is new to the author because of a personal experience he has recently had with respect to his own baby and his mother who is far away. He provides references to back up the idea that the existence of grandmothers in human history may have played a role in ensuring the survival of babies and young children. He does not belittle grandmothers, nor does he (or the hypothesis he is writing about) suggest that all women over 50 are otherwise useless and should hurry up and stop doing whatever they’re doing and go watch some grandchildren. Please take a deep breath. In no way is this a denigration of women over 50. I am a 60-year old woman who’s worked my whole adult life in what I consider a career, had 2 children, and look forward to potentially helping my kids if and when they seek my help. My family could not have managed without my own mother’s (and father’s!) occasional, but vital, help when my kids were small and we had to call upon them. My mother had a career, too, and that was not typical in the 50s and 60s when I was a child. My grandmother helped my mother to have a career as well. I am proud to call myself, my mother, and my grandmother feminists. Take a deep breath, everyone! Don’t shoot the messenger.

  • Please ladies and gentlemen, raise your white flags and improve the level of this most significant discussion

    We’re grand parents of 8 marvelous girls and boys and we’re happy to take care of them from time to time, to support our busy children. It’s a matter of proportion. No grand mother or father will accept to be “enslaved”, but let’s allow the natural flow of love and grandchildren enjoyment

    By the way, what’s going to say the evolutionary biology science when we’ll cross the non return “+2 oC” threshold as a result of billions of CO2 tons currently pumped by China, Russia, the US and the rest of the world ?

  • Is this article sarcasm? Or just patriarchy using spurious science to justify relegating wonen’s experience to only valuable if it serves men. Why do men who can no longer get erections continue to live? Most men start having erectile disfuction in their 40s. Men always assume that their existence is justified and good. I look forward to the article that explains the “slavery effect” —how cultures that enslave others have an evolutionary advantage by saving their offspring from the brutal effects of manual labor. Oh but you’d never print that because it would, rightly, be unethical.

    • Pat, I suggest that you read the references linked in the article. This is well established science, not created to “justify” people’s “existence”, but to examine why humans are different from most other animals.

      I am not sure why you think that rearing one’s own children and grandchildren just “serves men”. Indeed it is this rearing that has made the entire human species such a tremendous evolutionary success.

      While the fertility of males does decrease as they age, there is no abrupt end to it, like menopause in females. Why is there menopause in females? While you may think that question is irrelevant, nature does not care what you think, an actual reason does exist, and scientists are interested in knowing that reason because it may affect our health and future.

  • In the post WWII era, my Japanese-American parents raised our family in a multi-generational home, due to financial difficulties encountered from having been pulled from their educations to be incarcerated during the war, leaving many w/o jobs that provided substantial enough incomes with which to raise a family, having been released from the camps at the end of the war. My mother’s parents pretty much raised three of us while our parents worked multiple mundane jobs and came home only to sleep, eat and wash up. It was an extremely difficult time for my mother, as she was also left a widow with a 2 y.o.,
    5 y.o. and an 8 y.o.
    There is no doubt in my mind that without our grandparents to raise us, we would surely not have survived as well as to have become the professionals in medicine and physics we are today.

  • I totally disagree with Frank Samuelson. I will be direct : the MD’s article speaks of self-pity for not having grandma imported to raise the kids. The writer promotes return to antiquated values of grandmothers sacrificing their own after-kids lives to rear their children’s kids. These notions are from a culture that is outdated in the Western World in 2019.

    • You missed the point of the article entirely, Chris M. This article is on a web site that delivers “journalism about life sciences”, not culture or society. The title of the article is, “‘Grandmother effect’ helps explain human longevity”, not “My mother can’t spend time with my kids”.

      The core of the article is about the research published in several very reputable scientific journals. The rest of the article is “human interest” fluff that some editor probably required of the author. It is too bad that many readers cannot see the forest for the trees, and feel the need to be righteously indignant about other people’s cultures, rather than appreciating interesting science.

  • I am amazed at how many commenters do not understand the point of this article. The article is about the science of how humans evolved to be different from other animals. And quite fortunately our opinions on education, careers, society, religion, privilege, entitlement, fulfillment, etc. are completely irrelevant, and do not change human evolutionary history.

    • Why are you so upset by the comments? My biggest issue is that the author said the research suggests “The effect on longevity was seen mostly with maternal grandmothers and not paternal grandmothers.” Yet, he wants his mother. That will in no way improve longevity for his child. I would definitely not get a medical opinion from him.

    • Matt, you are misunderstanding the causal relationship. The theory is that at some time in human history there were mutations that caused humans to live longer, well past their periods of fertility. Typically this is not helpful to a species, because younger animals have to compete for resources with older animals. However if those older animals (humans) nurtured the younger ones, it improved the chances that those younger humans survived and reproduced. The longevity mutations were passed through genes from the older humans to the children and grandchildren who were now more likely to survive. Therefore a larger and larger fraction of the human population inherited the longevity genes and the entire species lived longer and nurtured their grandchildren.
      The author does not think that his mother giving care will improve his particular child’s longevity. The story about the author’s mother is just a modern human-interest touchy-feely anecdote and a consequence of the above-described step in human evolution.

  • The expectations you try to push are completely void of respect for any accomplishment and life desires of women with education and careers: the very same grandmothers you demote to un-evolved “female humans”. You show zero respect for THEIR life fulfillment. Grandmothers now are active producers who HAVE raised children. It is YOUR turn, to truly raise your own offspring. This seems a foreign concept to you.

  • My mother was viciously abusive to all of her kids. There was a large number of us because the Catholic Church wouldn’t allow her to use birth control methods that worked. Our father wasn’t around much because he had to work multiple jobs to feed and house us (he was a blue-collar guy, not a cardiologist). Half of my siblings chose not to have children. The other half would cut off their own limbs before allowing “grandma” to be alone with their children for even a few minutes.

    There are many other, more immediate and tangible, forces at work in human life besides evolutionary biology. Religion, for example. And economic hardship. People who are fortunate enough to benefit from nice grannies willing to provide free babysitting should thank their good luck rather than presenting it as some kind of inevitability to which they are entitled by Nature Itself.

  • It’s sad that your mother couldn’t come into the United States however I know that your practice and becoming a cardiologist means a lot to you and because your mother cannot help you at this time I know that’s the process Of becoming a cardiologist will be longer however I understand that your mother should be able to see her grandmother one day and enjoy the benefits of having her grandmother around today I believe grandmothers play a vital role in the growth in the process of children being rear And your article helps us to understand that it is something that been in the process of childbearing parents and grandparents and it’s important

    • Privileged professionals have the perfect excuse for turning their mothers and mothers-in-law into unpaid servants: “Evolutionary biology made her do it.”

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