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May 28, 2003

BLOOD AND GUTS

There is an interesting study in a recent issue of Science:

Science, March 7, 2003, vol. 299, pp.1582-85: Daniel Falush et. al.: Traces of Human Migration in Helicobacter pylori Populations (and commentary by Brian Spratt at pp. 1528-9).

Helicobacter pylori is a bacterium that lives in the human gut. It is transmitted mainly by prolonged physical contact, especially from mother to child. Within the gut, different strains of the bacterium recombine freely with each other. The phylogeny of the bacterium should therefore track the phylogeny of the human host population, diverging when different groups are separated, merging when they are united.

Falush et. al. have used analysis of Helicobactor to trace a number of important human migration events: the Polynesian colonisation, the spread of the Bantu in Africa, the occupation of the Americas, and so on. The results are generally consistent with genetic analysis of humans (Cavalli-Sforza, etc.). For Europe, the results are difficult to analyse, because there has been considerable mixing between groups of different origins. The authors however believe the European strains probably originate from two main sources, one from the direction of central Asia and one from the Near East and North Africa.

The commentary by Spratt is cautious about the prospects of resolving controversies about human ancestry with Helicobacter. The method is mainly useful when groups have been isolated for long periods (like the Maoris), but more problematic when populations have mingled. However, Spratt suggests that the statistical tools devised for the analysis may also be useful when applied directly to human genes, and not just bacterial ones.

DAVID BURBRIDGE

Posted by David B at 02:39 AM