Researchers at the University of Provence have found that people living in areas that were once part of the Roman Empire are less likely to have a gene variant that protects from HIV.

In countries inside the borders of the empire for longer periods, such as Spain, Italy and Greece, the frequency of the CCR5-delta32 gene, which offers some protection against HIV, is between 0% and 6%.

Countries at the fringe of the empire, such as Germany, and modern England, the rate is between 8% and 11.8%, while in countries never conquered by Rome, the rate is greater than this.

However, the researchers do not believe that the genetic difference is due to Roman soldiers or officials breeding within the local population – history suggests this was not particularly widespread, and that invading and occupying armies could have been drawn not just from Italy but from other parts of the empire.

Instead, they say that the Romans may have introduced an unknown disease to which people with the CCR5-Delta32 variant were particularly susceptible.

It might just be a correlation. Other researchers think the difference in frequency of this gene variant may be related to the spread of other diseases like the Bubonic Plague.

If people without the gene were more susceptible to die from the plague or whatever other nasties, say, then the gene would be more frequent among the survivors in the hardest hit areas.

I read in another article that the pattern doesn’t match the plague map as well as it does the Empire, though.

Alternative theories include the idea that the protective variant originated in Scandinavia, and was spread north and east by the Vikings. But the pattern of Viking migration does not match the current distribution of the variant. Another theory is that a major disease, such as plague or smallpox, created a selection pressure on the gene variant which increased its frequency. But its distribution does not match that of disease outbreaks, either.