Grannies live long and prosper

Researchers offer an evolutionary explanation for postmenopausal women sticking around: child care

By Toss Taylor

"I want to stay with Nanny!" If you've heard this plaintive wail from any of your offspring lately, cut the little darlings some slack. It may not be just the baked goods, or the loonies she sneaks into their palms, making them want to linger at Nan's house. It may not even be because they know there's a pretty good chance she'll let them stay up late and not make them do their homework (though that surely plays a part). It seems there's actually a deeper, scientific explanation for the bond that exists between grandmothers and the apples of their eyes.

The phenomenon of women living long after childbearing age is fairly unique to humans. A team of scientists from Finland, Canada and the UK decided to delve into the reasons in hopes it would shed some light on whether postmenopausal lifespan has any fitness benefits. What they discovered is that though many of us believe that longevity is a modern trend thanks to medical advances, the fact is women always lived longer than men � and for reasons other than homemade cinnamon rolls and birthday parcels. If you dropped the kids off at your mum's place on the weekend so you could have some 'me time,' you're getting warmer. Yes, it's true: postmenopausal women have been naturally selected as cheap babysitters.

The study, published in a recent issue of Nature, looked at two populations in Finland and Quebec in the 18th and 19th centuries and found that for each decade a woman lived past menopause her offspring produced two grandchildren. Sons and daughters whose mother was still living tended to have more children and earlier. The researchers hypothesize that's because they could rely on their mother to help look after the firstborns while they carried on popping out more babies.

What's more, the mortality of the babies was vastly improved by having grandma around to keep an eye on them � 12% more grandchildren with grandmothers under 60 lived to adulthood (this benefit dropped to 3% if their Nan was older, especially if she lived in another village). Interestingly, this so-called 'grandmother effect' only began after the children had been weaned. On the downside, a grandmother's own mortality encroached more rapidly when her children stopped reproducing � which the researchers interpret as a biological passing of the caregiver torch to the next generation.

These findings have significant ramifications for our own age. For one thing, it forces us to shift our thinking away from the aging population as a burden. As Dr Kristen Hawkes, PhD, points out in her accompanying commentary, this suggests that "instead of help

for older members of the population, it is help from postmenopausal grandmothers that accounts for the age structures of human societies."

With 70% of mothers in Canada working outside the home, we're depending more than ever on our parents to lend a helping hand for child care. About 37,000 grandmothers are single-handedly raising their grandchildren in Canada and about 474,400 grandparents live in 'sandwich' households with their children and grandchildren, an arrangement that often involves a child care/elder care exchange.

A word of advice: "Mum, how about fulfilling your destiny and minding the kids this summer?" might not be the best approach for asking a favour....