The work of Virpi Lummaa has been getting a lot of attention recently. Last week I discussed one of her studies, published in the Proceedings of the National Academy of Science, that found women who were the twins of males showed less fertility than women who were twins of women. But she is mining a very unique data set for some other fascinating findings.

The data set she is working with is turning out to be a gold mine in addressing a number of theories regarding human evolution. These data are so valuable because they were collected from five diverse towns in Finland between 1734 and 1888. These preindustrial towns were not impacted by any modern birth control methods or even modern medicine and nutrition. In fact 40% of children died before they reached adulthood, even with a definition of adulthood being 15. So while these data reach back nearly three centuries they provide meticulous detail and the comprehensiveness of the birth and death patterns for these entire towns providing a one of a kind opportunity for researchers to understand the impact of various evolutionary forces on reproduction.

One question this data can address is the age old mystery of why women live so long after they are no longer able to reproduce. Most other animals’ lifespan is closely related to their reproductive span, including male humans. Dr. Lummaa discusses in the July 16 2007 Scientific American, how she has been able to address this question with this data on 18th and 19th century Finns.

One obvious theory as to why women live into menopause is that they enhance the reproductive chances of their grandchildren. In fact in analyzing this data, along with some additional data Dr. Lummaa collected from pre-industrial French Canadians, she found that women with grandmothers had more children at a younger age. More importantly, these children had an increased chance of surviving to adulthood. This seems to suggest that one reason women live well into menopause is because of the help they provide to future generations.

The obvious follow-up is, “What about Grandpa?” If grandmothers improve survival odds for their grandchildren what do elderly males contribute? Lummaa’s data actually suggest that having a grandfather brings with it a negative effect on the longevity of future generations. Specifically, young women with a grandfather tended to have fewer children surviving to adulthood. Dr. Lummaa has a number of possible explanations; cultural traditions that cater to older men may mean that grandpa is getting some of the offspring’s share of the food; or maybe because men can continue to reproduce they are less invested in anyone other than their own children.

The availability of meticulously recorded information on preindustrial families is providing a new look at human evolution. It is unclear what effect these patterns observed hundreds of years ago have on us in this day of reproductive choice and MRI’s. But it does point out that human evolution has long selected for events that are not directly related to individual reproductive fitness. Most of us think of evolutionary fitness and think of the young, fit, lean and mean. But now we need to add the care and nurture provided by grandmothers to our understanding of how evolution works.