Thoughts in a Haystack

Helicobacter pylori is a bacteria that causes ulcers and stomach cancer in human beings. An international team of researchers led by microbiologist Mark Achtman of the Max-Planck Institute for Infection Biology in Berlin has been collecting samples of the bacteria from the guts of humans from around the world since 1999 and, at last count, had gathered 532 strains of H. pylori from people belonging to 51 ethnic groups. The researchers then sequenced seven gene fragments from the DNA and:

... used population genetics models to sort the strains into clusters that showed their genetic and geographic patterns. People from east Africa had the most kinds of H. pylori. The further people lived from east Africa, the fewer strains the researchers found. This suggests that the bacteria arose in humans in east Africa, because it would take more time to accumulate so much diversity -- and because the root of all the clusters was in east Africa. Conversely, fewer people -- and, thus, fewer bacterial strains -- reached the hinterlands where the bacteria had less time to accumulate genetic mutations.

While there is already much genetic evidence that H. sapiens originated in Africa, the timing of the spead of humans out from there has been variously put at a point earlier than 100,000 years ago or as recent as within the past 60,000 years.

In the new report, the researchers use computational simulations to date the spread of H. pylori out of Africa to about 58,000 years ago, which supports a more recent migration out of Africa. "The real novelty here is the timing," says population geneticist Keith Crandall of Brigham Young
University in Provo, Utah.

The report does not address two other controversial questions -- whether modern humans swept out of Africa in one or multiple migrations, and whether modern humans completely replaced the archaic people they encountered in Europe and Asia.

What? No mention of Mount Ararat?
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