Sunday, April 22, 2018

American Nations As Revealed In Identity By Descent (IBD) Networks


medium  |  Earlier this summer, I presented the American Nations: the eleven regional cultures that comprise the United States and North America. Their existence explains much about our history, our constitutional arrangements, and, indeed, our political fissures — past and present. If you have any ancestors who were living in North America prior to the Civil War, the existence of these rival nations is likely reflected in parts of your family tree and, according to a recent study published in Nature Communications, may very well have left a mark on your DNA.

I couldn’t miss this study, because shortly after it came out, readers of my 2011 book, American Nations: A History of the Eleven Rival Regional Cultures of North America, were stuffing my inbox and flooding my social media feeds with it. A glance at the thumbnail illustration that accompanied the study made it clear why: Unbeknownst to the scientists who’d written the paper, the map depicting the key results of their research on the patterns of genetic variation in North America over time and space mirrored the American Nations map to an uncanny degree.
Here they are for comparison:










This is remarkable because the American Nations paradigm is resolutely not about genetics or genealogy. Rather, it’s built on the late cultural geographer Wilbur ZeFrolinsky’s Doctrine of First Effective Settlement, which argues that when a “new” society is settled, the cultural characteristics of the initial settlement group will have a lasting and outsized effect on the future trajectory of that society — even if their numbers were very small and those of later immigrants of different origins were very large. These lasting characteristics, which inform the dominant culture of entire regions of North America, are passed down culturally, not genetically, which explains why the Dutch-settled area around New York City still has obvious and distinct characteristics inherited from Golden Age Amsterdam, even though the portion of people there reporting Dutch ancestry to census takers is a vanishingly small 0.2 percent. Culture is learned, not inherited.

And yet the Nature study — powered by the enormous cross-referenced genomics and genealogy databases of Ancestry.com — reveals that the regional cultures have left a significant genetic imprint as well. That’s because members of a regional culture tended to mate with one another, rather than with people from rival areas, even when those rivals lived nearby, in the very same colony or state.
“Who we are today — the genetics of Americans all over the place — is the result of all kinds of cycles of reproductive isolation and the release of that isolation,” says Catherine A. Ball, a geneticist and the chief scientific officer at Ancestry who oversees the company’s DNA work. “Who your mates would be was linked to geography, politics, religion, war, and all of that is showing today in people walking on the streets and who they are related to.”

Ball wasn’t familiar with American Nations before I spoke with her, but the results show that the boundaries of the regional cultures were very real when it came to human reproduction, creating reproductive clusters centuries ago that geneticists have been able to recreate through the examination of nearly a million living Americans’ DNA.