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Evolution confirmed! Urban humans evolved immunity to TB

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In places with a long history of urban living, a genetic variant which reduces the chance of contracting diseases such as tuberculosis and leprosy, is more prevalent. Nowadays, cities’ inhabitants are more likely to possess the genetic variant.

In ancient cities, poor sanitation and high population densities would have provided an ideal breeding ground for the spread of disease. If, in the early days of city life, anyone had a gene which conferred some small degree of protection against infections, over time in long-standing urbanized populations, their descendants possessing the gene will be more resistant to disease. It is because natural selection means anyone without the protective gene is more likely to die, leaving more people with the gene behind. The general population of the city therefore gradually gets more immune to the diseases of urban life like TB. It is, though, hard to confirm in practice, especially in prehistory.

Scientists from University College London (UCL) and Royal Holloway have now searched archaeological and historical literature to find the oldest records of the first city or urban settlement in 17 different human populations living across Europe, Asia and Africa. Then they were able to confirm evolution of disease resistance in city populations in these regions by analyzing DNA samples. Dr Ian Barnes, from the School of Biological Sciences at Royal Holloway, said:

The method we have employed here makes novel use of historical and archaeological data, as a means to explain the distribution and frequency of a genetic variant, and to identify a source of natural selection. This seems to be an elegant example of evolution in action. It flags up the importance of a very recent aspect of our evolution as a species, the development of cities as a selective force. It could also help to explain some of the differences we observe in disease resistance around the world.

By comparing rates of genetic disease resistance with urban history, they showed that past exposure to pathogens led to disease resistance spreading through populations, with our ancestors passing their resistance to their descendants. Professor Mark Thomas from the Department of Genetics, Evolution and Environment at UCL said:

The results show that the protective variant is found in nearly everyone from the Middle East to India and in parts of Europe where cities have been around for thousands of years… Population density seems to play an important role in shaping so many aspects of our species. It was a vital factor in our species maintaining the complex skills and culture that distinguish us from other primates. It drove many of the genetic differences we see today between different populations from around the world. And now, it seems, it also influenced how infectious diseases spread in the past and how we evolved to resist those diseases.

Written by mikemagee

24 September, 2010 at 11:27 am

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