Researchers, including a team at Ohio State University, have traced a genetic mutation that causes the most common form of inherited colon cancer back 500 years, probably to early American Indians, and discovered that even more of us carry it.
This is bad journalism. In the original journal article which gave rise to the story, researchers actually claim (my emphasis):
data are suggestive of an earlier founding event than was first thought, which likely occurred in a European or a Native American population.
As we shall see, evidence for the "Native American" theory is quite thin.
The researchers start with 40 families who carry the mutation (most of whom come from Kentucky, Ohio, or Texas) and manage to link these into seven "subfounder" pedigrees most of whose "founding couples" were born or married in southwestern Virginia, western North Carolina, or eastern Tennessee in the late-18th or early-19th century. So far, so good.
With this in mind, we are left with two hypotheses, both of which are supported by the mutation age calculations. Either, the subfounder families were in the United States for several generations before that of the current subfounder common ancestors, which would allow for the possibility that the mutation was either brought into the United States by a single European immigrant during an earlier period or that the mutation had been introduced into these European lines by a Native American individual during this early colonial period. Or, the mutation originated within Europe several generations before it arrived on the shores of the United States, probably through several individuals.
The lack of evidence for the AFM outside of the United States is perhaps more supportive of the first hypothesis; however, there also lies the possibility that most of the possible carriers of the mutation in Europe may have emigrated or that many failed to pass on the mutation to subsequent generations and so we might predict a significant reduction of cases, or even an absence of cases in the founding country. In addition, our search for the AFM in Europe has by no means been exhaustive, so it is still possible that there are AFM mutation carriers in Europe that we have just not been able to identify yet. We have speculated, based on our genealogic studies, that Scotland in particular is a potential European source for the mutation; however, we have only been able to identify a single candidate (individual with a known exons 1–6 deletion of MSH2) from this region, who was shown not to carry the AFM. In addition, samples we have screened from an ancestrally related population (Ireland) were also negative for the mutation, and to the best of our knowledge, it has not been described elsewhere in the British Isles. Until evidence in support of one of these two hypotheses is obtained, whether it is the identification of a single common ancestor within the United States or the presence of a case of the AFM in another country, we cannot make firm conclusions as to the origins of this mutation.
Notice, when looking for evidence of the mutation outside America, the researchers did not look in England. English was only the primary component in the ancestry of colonial Virginians. But, since the researchers "speculated" that Scotland was a potential source of the mutation, I guess they decided it was unnecessary to check in England (they did see fit to check samples from France, Sweden, Italy, Poland, Germany, Ireland, and Scotland).
Nor, of course, do the authors report finding the mutation in Amerindians, but they apparently don't consider it worth mentioning this point as evidence against the "Native American" hypothesis. How did "Native Americans" get drawn into this story to begin with?
Various families in most of the subfounder groups also have reported Native American ancestries, specifically Cherokee
"Various" out of 40 families with roots in Kentucky and/or Texas claim to have "Cherokee" ancestry? What are the chances of that? If only the researchers had probed a bit further, maybe they could have narrowed the elusive ancestor down to a "Cherokee princess".
but thus far this seems verifiable in only three or four families.
I'm shocked. And, of course, the "verifiable" Amerind ancestry in this 8-10% of the families evidently does not come by way of the "founding couples", and thus is almost entirely irrelevant to the study.
These Native American links are certainly possible because the geographic placement of the progenitor couples, as given above, is either just inside or very close to the known Cherokee territorial boundaries of the time.
As were the ancestors of many westward migrating Southerners at the time. The map below shows claimed Cherokee territory prior to European contact (broadest expanse encompassed by black borders), in 1791 (intermediate black borders), and in 1838 (small, red borders; source).
I've added letters to indicate earliest known locations of "founding couples" (after Figure 2 in the paper under discussion, "wherein A, C, D, and E correspond to marriage locations of the common ancestors, and B, F, and G correspond to the regions that the common ancestors were born in").
All the birth locations of "founding couples", where known, are northeast of the widest claimed expanse of the Cherokee nation (the borders of which contracted southwestward over time). Considering that the flow of settlers overwhelmingly pointed west (not east) in this time period, this map hardly supports the Cherokee theory. Chances are, the common ancestor lived even farther east. To me, all evidence suggests the ancestor either lived in Europe or was an early (17th-century, probably English) settler of Virginia. It's not impossible the ancestor was Amerindian, but the authors have presented no good evidence in favor of that hypothesis.
The pedigrees (including links to Rootsweb WorldConnect databases) and a copy of the paper are available here.
Clendenning et al. Origins and Prevalence of the American Founder Mutation of MSH2. Cancer Research 68, 2145-2153, April 1, 2008. doi:0.1158/0008-5472.CAN-07-6599
(Story via The Genetic Genealogist.)