City living helped humans evolve immunity to TB

New research has found that a genetic variant which reduces the chance of contracting diseases such as tuberculosis and leprosy is more prevalent in populations with long histories of urban living. The research, published in the journal Evolution, shows that in areas with a long history of urban settlements, today's inhabitants are more likely to possess the genetic variant which provides resistance to infection. In ancient cities, poor sanitation and high population densities would have provided an ideal breeding ground for the spread of disease. Natural selection should mean that humans would have developed resistance to disease in long-standing urbanised populations over time. However, this association has been very difficult to assess - especially in prehistory. Now, scientists from UCL (University College London) and Royal Holloway have tested the theory by analysing DNA samples from 17 different human populations living across Europe, Asia and Africa. In addition, they searched archaeological and historical literature to find the oldest records of the first city or urban settlement in these regions.