People from traditionally urban areas could be genetically better suited to fighting infection

Researchers looked at how many people carried a specific gene variant known to give them resistance to TB and leprosy. It was more common in those from areas with a longer history of urbanization, where the diseases were more likely to have been rife at one point. The phenomenon is suggested as an example of selective pressure in relation to disease resistance. It happens because, when a population is exposed to a killer illness, the people who are best placed to pass on their genes to the next generation are those whose genetic make-up helps them fight the infection. In towns and cities, where people intermingle far more closely, the likelihood of being exposed to infectious disease is theoretically higher. So, over the centuries, the greater the level of historical exposure, the more likely it is that these resistance genes will be spread widely among the population. The scientists tested this by analyzing DNA samples drawn from 17 different human populations living across Europe, Asia and Africa. The results were cross checked against historical and archaeological data about the date of the first city or urban settlement in each region. The protective gene variant was found in nearly everyone from the Middle East to India and in parts of Europe where cities have been established for thousands of years, but was less frequent in regions with a shorter history of urbanization, such as Africa.