On the Origin of Grandmas

Visiting the grandparents is a time-honored tradition here in America. We pile into the minivan, Chips Ahoy and Travel Yahtzee at the ready, and drive for an eternity. Then upon arrival, exhausted and dehydrated, we are immediately smothered by sloppy grandmotherly kisses, immense amounts of food, questions, cuddles and, of course, lots and lots of presents.

Long-distance grandparents are a fact of the modern world. Job opportunities and advanced schooling pull parents from one urban center to another, leaving hometowns and family circles behind. According to a 1997 survey from the American Journal of Sociology, fewer than 60% of U.S. women live within an hour’s drive of their parents, meaning that many grandparents have been relegated to matters of vacations, Christmases and birthday cards.

This peripheral role of grandparents is a relatively new phenomenon – especially for grandmothers. For thousands of years grandmothers helped with child care, domestic chores, even food gathering. In fact, anthropologists have argued that the effect of grandmotherly care on child survival was so potent that it shaped some of our most basic biology: menopause, cognitive decline, even longevity itself.

These evolutionary benefits of grandmothering evaporate when grandmas no longer live with (or near) their grandchildren. Studies have also suggested that only youthful grandparents provide discernible benefits to child health. So as the distance between grandparents and children grows, both in geography and in age, does this spell the end to the grandmother effect?

The Grandmother Hypothesis
Ten years ago, Kristen Hawkes, an anthropologist at the University of Utah, was examining the biological basis and evolutionary origin of menopause in humans. Her observations led to the so-called “grandmother hypothesis,” which suggests that grandmas reap an evolutionary boon from ceasing reproduction in their fifties and just helping to raise the grandkids. Hawkes’ idea rested on the fact that as women age, pregnancy-related health problems rise dramatically. For example, the incidence of Down syndrome rises from 1 baby in 1,490 when a mother is 24 to 1 in 160 when she is 40. At 50, the risk is 1 in 11. Older mothers are also at a greater risk for high blood pressure, gestational diabetes and difficult labors – first-time mothers 35 and older are almost seven times as likely to have C-sections or assisted deliveries.

Initially, criticism of Hawkes’s hypothesis was harsh: biologists argued that tying the biological basis of menopause to the cultural aspect of grandparenting was just bad science. But in the past decade a handful of empirical studies from around the world have emerged. Each has found hard evidence that grandmothers benefit their grandchildren’s survival and growth, and hence the number of her own genes that survive to subsequent generations.

A 2005 study led by Mhairi Gibson at University College London and published in Evolution and Human Behavior showed that, in rural Ethiopia, children who had lost both grandmothers had a significantly higher risk of dying before the age of three, compared with those with either one or two grandmothers alive. 

A 2004 Nature study, led by Mirkka Lahdenperä at the University of Turku, Finland, examined the life-history records of families from eighteenth and nineteenth century farming communities in Quebec and Finland. This study, too, showed a connection between the number and survival rates of grandchildren and years a grandmother was around to help.  Indeed, their results showed an increase in survival of the grandchildren by 16%, if the grandmothers were alive as the grandchild grew up. 

Long-Distance Grandmothering
In the Ethiopian study, the proximity of grandmas to their grandchildren significantly increased child survival. But in Lahdenperä’s study, the local-grandma effect took a nosedive when the grandmother was over 60 at the time of the child’s birth. Survival to adulthood was enhanced by 12% for under-60 grandmothers, but by only 3% for kids with older grandmas.

What’s more, evidence suggests that the grandmother effect has influenced the age when our brains start to fail. Yep, right around 60. A 2005 study led by John Allen from the University of Iowa, in the American Journal of Human Biology, found that in most people, brain function does not begin to decline until age 60.  Allen’s study used cognitive ability tests and measured overall brain volume in individuals both over and under 60 to reach these conclusions.  The study not only supports the grandmother hypothesis, but also suggests a reason why older grandmas aren’t as good as younger ones.

Today’s grandparents are getting older and often living farther from their grandkids. Though the average age of first-time grandparenting is still around 50 years old, the age of first birth for moms is creeping ever upward. According to the U.S. Centers for Disease Control, the average age of first-time mothers was 21.4 years in 1970. It crept up to 25 years by 2000. This figure is the combined effect of fewer teen pregnancies and a significant surge in the number of women having babies in their thirties and even forties.

Modern Grandmas: Money Knows No Age Limits
While parents are getting older on average, increasing life expectancies means grandparents are more than making up the difference. Since 1950, combined male and female life expectancy has climbed from just 68.2 years to 78.8 in 2004. So even if first baby arrives when parents are fortysomethings, grandparents have a good chance of still being alive and healthy, even if their brains have started to shrink.

While almost 2% of U.S. grandparents live with their grandkids and provide full-time care, the most common type of grandparental support these days is just plain money, a resource that travels across vast distances and is (nearly) impervious to cognitive decline. The American Association of Retired Persons estimates 52% of grandparents help to fund their grandchild’s higher education, and a significant percentage of grandparents also help with medical costs and living expenses. While it might not be the same as helping to gather food or help a new mother with domestic tasks, it may just be the modern-day equivalent for the generally well off. Education level is highly correlated with socioeconomic status, which in turn is related to overall health and longevity, so perhaps putting the grandbaby through Harvard is sort of like bringing home a basket of wild veggies every day for 18 years.

So, though the modern grandparent might be getting a bit fuzzy in the head and weak around the hips, it doesn’t mean they can’t lend a hand in the evolutionary sense. Even in this modern age, it would appear that modern society has not killed off the grandmother effect, it’s just forced it to evolve.