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Fertility on the (Canadian) frontier — and its modern health implications

A region’s original wave of settlers, like this Minnesota family, would have contributed more to its gene pool than later arrivals.
Courtesy of the Minnesota Historical Society
A region’s original wave of settlers, like this Minnesota family, would have contributed more to its gene pool than later arrivals.

Women who were among the first wave of non-native pioneers to settle a wilderness area of northeastern Quebec in the 17th century had more children and grandchildren than the women who stayed behind — or who came to the area in subsequent waves of settlers — according to a new study published in Science magazine.

Besides being historically intriguing, this finding may have some medical importance. It may explain why rare genetic diseases appear at a higher-than-average rate in particular geographic regions. According to this study’s findings, a region’s original wave of settlers would have contributed more to its gene pool than later arrivals. So, if anyone within those first — and more fertile — families had a rare gene variant, that variant was more likely to be passed down to future generations.

In the case of northeastern Quebec, writes Science reporter Ann Gibbons in her article summarizing the study, “some 30,000 settlers, mostly farmers, who opened frontiers starting in the 17th century passed on up to four times as many genes to living people than did immigrants who lagged behind in core towns.”

Four-plus centuries of data
For the study, researchers examined the marriage, birth and death records of 84 parishes in the Charlevoix and Saguenay-Lac-Saint Jean regions of Quebec. The records involved 5 million people who settled and lived in those regions between 1608 and 1970.

With the data, the researchers were able to follow European immigrants (mostly French) as they spread out through the area.

The data revealed that the families who lived closest to the frontier had the most children. Writes Gibbons:

By comparing birth and marriage records, the researchers found that women on the leading edge of the wave had an average of 9.1 children, compared with 7.9 children per family at the core, a boost of about 15%. That increase was amplified in their offspring: An average of 4.9 children from front-line families married compared with 4.1 at the core, a 20% difference.

A matter of resources?
What caused the frontier women to have a higher fertility? The study suggests, as Gibbons notes, a couple of explanations:

It could be partly due to cultural preferences, such as the benefits of having a large family. Or it might be that “fertility is highest at the wave front because there are more resources [there],” explains population geneticist Henry Harpending of the University of Utah in Salt Lake City, who was not part of the study. “As a place fills up, fertility declines in response to fewer resources. This paper shows that is exactly what happened.”

The study (and Gibbons’ summary of it) appear in the Nov. 4 issue of Science. Unfortunately, both are behind paywalls.

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