The results are somewhat puzzling, comments Kenneth Weiss, a biological anthropologist and geneticist at Pennsylvania State University. He notes that “if twinning is genetic, then there should be a slight selection bias against it, so that twinning would be kept rare. But some animals twin routinely.” Given the seeming conflict, he says, “there are dangers in overinterpreting ‘fitness’ effects, even if the observation is correct.”
That danger is especially acute when trying to apply the results to the present day. Access to effective birth control, an abundance of food, and low child mortality rates would all obscure the evolutionary influences seen in the preindustrial data. “It’s almost a shock when you realize that 100 to 150 years ago, 40 percent of babies died before they reached adulthood,” even when adulthood was defined as age 15, Lummaa notes.
But most of the world’s population still lives under similar conditions to those faced by preindustrial Finns. “Who gets the most kids and who puts forward the most genes are still going to be the people who make up the next generation,” Lummaa says. “There is no reason why the principles of evolution wouldn’t apply.” And she hopes to test her Finnish findings against more modern demographic information, such as the ongoing collection of health records for families in the Gambia, on Africa’s west coast.
Lummaa and her colleagues have also begun to parse the Finnish records to understand grandparents and the evolutionary conundrums they pose. Her group’s previous research has shown that grandmothers provide direct aid in ensuring the survival and reproduction of their grandchildren. The same records revealed, however, no such benefit from fathers and grandfathers. Whereas having a father around did seem to aid children in getting married earlier, a living papa did not increase the number of grandchildren.
“If anything there’s a negative effect,” she concludes. This could be because of the cultural tradition of catering to men, particularly old men. “Maybe if you had an old grandpa, he was eating your food,” she speculates.
Or, possibly, longevity in men is simply a by-product of selection for longevity in women. And it could be that because men can reproduce throughout their lives, they are less vested in anyone other than their own children; Lummaa is examining whether men continue to procreate into old age, although a monogamous culture such as Finland’s argues against it. “Men past 50 had a chance of finding someone who wanted them,” unlike a woman past childbearing years, Lummaa says. “What, if any, benefits do men get from reaching old age?”
Lummaa and her colleagues are also using the data to explore issues of class, showing that the rich in olden times produced more heirs than the poor. Populations in the richest parts of the world seem to have reversed that long-standing trend.
“Perhaps under the current circumstances, we are investing in quality over quantity,” Lummaa speculates. “The satisfactory answers are still kind of missing.”
But the deleterious effects of males—and the benefits of grandmothers—stand out clearly. This does not bode well for Lummaa, who gave birth to a son, Eelis, in March. “I can certainly see that it’s taking a lot of energy, and I’m sure it’s aging me,” she chuckles. “How on earth these women managed to give birth every year is truly amazing.”
And certainly there will be no shortage of sons, despite their costs. “If you produce a really, really good son, he can produce a lot of offspring,” Lummaa notes—the best outcome from an evolutionary standpoint. “You might lose more by producing a son, but you might win more as well.”