Saturday, May 2, 2009

Origin confusion?

Science Magazine and the New York Times both reported this week on a new Africa-wide survey of human genetics, the largest ever to be conducted in that continent, which claims to pinpoint more closely the geographic origin of modern humans.

Unfortunately, the two articles appear to report conflicting results.

The New York Times’s Nicholas Wade reports, “The origin of species is generally taken to be the place where its individuals show the greatest genetic diversity. For humans, when the new African data is combined with DNA information from the rest of the world, this spot lies on the coast of southwest Africa near the Kalahari desert.”

Science Magazine’s “news” section, in contrast, says the study concludes that “East Africa was the source of the great migration that populated the rest of the world.”

I wasn’t able to access the researchers’ data or original report (it may not be online yet), which probably clears up this apparent contradiction. I’m assuming that Science’s “great migration” and the Times’s “origin of species” are actually two different things.

Nontheless—confusing! Those are the kinds of quotes that news sources can run with, and which might spread misinformation. I’ll post an update/clarification whenever I can get access to the actual research (…or when something comes up on the New York Times’s “corrections” page?). Responses welcome if anyone can figure out where the confusion lies.

The study’s data provides a lot more interesting information besides that on the “origin" question. Africa, despite being the continent with the greatest genetic diversity, has been underrepresented in genetic surveys, especially because the most diverse groups (like bushmen and hunter-gatherers) are logistically difficult to reach.

This group of researchers spent over 10 years collecting samples from some of the most remote populations in Africa, eventually ending up with blood from 3194 Africans in 113 different populations. They then searched the samples for over 1000 genetic markers, and sorted the DNA into similar clusters.

They found (luckily for them!) that those DNA-based clusters mapped well onto cultural and language groups. For example, the click-language groups—such as the Khoisan of south Africa and the Sandawe and Hazda of Tanzania—share common ancestors.

Researchers also found, through comparison with African-American DNA samples, that most African-Americans have ancestors from all over Africa, making it difficult to pinpoint a person’s origins to a specific group (as some DNA testing claims it can do).

There is hope the data will be used eventually for medical research--for example, to better understand why people respond differently to diseases and drugs.


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Darwin Evolving said...
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