April 19, 2013 | 13
Odds are you carry DNA from a Neandertal, Denisovan or some other archaic human. Just a few years ago such a statement would have been virtually unthinkable. For decades evidence from genetics seemed to support the theory that anatomically modern humans arose as a new species in a single locale in Africa and subsequently spread out from there, replacing archaic humans throughout the Old World without mating with them. But in recent years geneticists have determined that, contrary to that conventional view, anatomically modern Homo sapiens did in fact interbreed with archaic humans, and that their DNA persists in people today. In the May issue of Scientific American, Michael Hammer of the University of Arizona in Tucson examines the latest genetic findings and explores the possibility that DNA from these extinct relatives helped H. sapiens become the wildly successful species it is today.
As Scientific American’s anthropology editor, I have an enduring interest in the rise of H. sapiens; and as longtime readers of this blog may know, I’m fascinated (you might even say obsessed) with Neandertals. So naturally I’ve been keen to find out how much, if any, Neandertal DNA I have in my own genome. Several consumer genetic testing companies now test for Neandertal genetic markers as part of their broader ancestry analysis, and after 23andMe lowered the price of their kit to $99 in December, I decided to take the plunge. As it happens, National Geographic’s Genographic Project had recently updated their own genetic test to look for Neandertal DNA, and they sent me a kit (retail price: $299) for editorial review, much as publishers do with new books. And so it was on a chilly Saturday in late January that I found myself spitting into a test tube for 23andMe and swabbing my cheek for the Genographic Project.
Of course the two tests look at far more than one’s Neandertal ancestry. 23andMe provides a wealth of health information, testing for variations in DNA that might affect disease risk and drug performance as well as mutations that could cause disease in one’s children. (I’ve decided to not look at those health results for now because I’m a worrier, although I may change my mind eventually.) Genographic’s test does not look for health information. Both tests trace one’s maternal lineage (and paternal lineage, for males) to beyond 10,000 years ago and reveal what percentage of one’s recent ancestry comes from various regions around the world.
Based on my mitochondrial DNA, which is passed down exclusively along the maternal line, both tests traced my maternal lineage to the Mediterranean 16,000 years ago (Genographic takes it all the way back to East Africa 70,000 years ago). I was interested to learn that my branch of the mitochondrial DNA tree is found in only about 3 percent of people in the British Isles, where my maternal great-grandmother came from.
My recent ancestry results were pretty much as expected—roughly half of my ancestry is European and half is east Asian; both tests further broke these regions down into smaller subregions. Intriguingly, the Genographic test hinted at a 2 percent Native American component, which I did not expect based on family lore. Yet this may not be what it seems. The Genographic site explains in a case study of a boy with a European mother and a Japanese father, “the 2 percent Native American actually reflects the fact that the ancestors of today’s Native Americans came from Asia, and reveals that there are still genetic patterns that they share from thousands of years ago.” The same may well apply to my result.
But on to the Neandertal business, because that’s what got me interested in these tests in the first place. Well, I’m pleased to report that both tests determined that I do, in fact, have Neandertal DNA. But interestingly, the tests differed rather significantly on how much I have. According to the Genographic Project, I’m 2.1 percent Neandertal (average for non-Africans, their site informed me). In contrast 23andMe found 2.9 percent Neandertal content. So what gives? Why the different results? As I pondered the results, other questions came to mind. Is there any way of knowing which stretches of one’s DNA have Neandertal origins? Will scientists eventually be able to tie one’s Neandertal DNA to observable traits? Might it be possible some day to pinpoint when and where my H. sapiens ancestors mated with Neandertals?
Genographic also found that I am 1.4 percent Denisovan, but they note on their site that they are still refining their approach to assessing Denisovan contributions. Frankly, I think it’s amazing that they assess this at all, given that the mysterious Denisovans were only discovered in 2010. I wonder how good they think their estimate is, and how it can be improved in the future. And I’d love to know how data from these personal genetic testing services are driving bigger research questions about the rise of modern humans (Hammer’s article includes a cool example of this.)
I’ll be reaching out to both 23andMe and the Genographic Project with these and other questions about their ancestry tests. Have you had your DNA tested for insights into your deep ancestry? Do you have general questions about how these tests work or what the results mean? Let me know in the comments below and I may pose them to the experts along with my own queries.