I noticed this entry on Time‘s Healthland blog, Study: City Life Spreads Disease, But If It Doesn’t Kill You…. The author ends kind of strangely:
The authors of the study expressed excitement about the merging of scientific analysis and historical records, but this is also a potential limitation. Scientific and historical conclusions are different in nature and difficult to merge — that is, you can’t necessarily extrapolate science from history. So it might be hasty to suggest that population density was the central contributing factor to the development of the anti-TB genetic mutation.
For one thing, the highest rates of the anti-TB variant occurred in Middle Eastern populations and in areas that were involved in prominent Arabic invasions — for example, Spain (711 to 1492) and India (in the 12th century) — and not in other areas that are home to ancient cities but were not subject to Arab invasion (China). So who’s to say that immunity isn’t a result of Arabic ancestry, rather than city life? Or that some other historical factor triangulated with urban centers to suggest this result?
Arabic is a language from what I know, Arabs are a people. So it was Arab invasions. Second, the Arabs did not invade India in the 12th century, they invaded Sindh in the 8th century. But Arabs never went further than Sindh, the Muslims who pushed into the rest of India were generally ethnic Turks or Iranians (Afghans in the latter case). Also, there isn’t much evidence that genetically the Arabs had an impact on the Sindh or Spain if you look at phylogeographic research. But there’s a bigger issue which rebuts the question mark introduced here, in the abstract of the original paper they state that they controlled for shared population history!
You can find the full review of the paper and my own thoughts on the relationship between diseases, cities, and genetics, over at Discover. UCL also put out a press release.