Thanks to our stay in crowded cities, our ancestors developed resistance to disease, reports New Scientist.
Some people have a sequence (allele) in their genes that provides resistance to leprosy and tuberculosis. Mark Thomas, an evolutionary biologist at University College London, and Ian Barnes, a molecular palaeobiologist at the University of London, concluded that this genetic immunity could arise when humans began to live close together.
In their opinion, poor sanitation in former cities was conducive to disease, but contact with germs led to the development of immunity, which was then passed on to descendants.
Thomas and his colleagues analyzed the DNA of people living in 12 regions of Europe, Asia and Africa. They also collected historical and anthropological data to determine when people first began living in closely related groups. As it turned out, the longer cities existed in a given region, the more likely the current inhabitants of those areas were to possess alleles of resistance.
Previously, it was believed that resistance to tuberculosis is due to the domestication of cattle – cows may be carriers of the strain of mycobacteria causing this disease. However, the allele was more closely related to the formation of cities than to the domestication of cattle. For Barnes, one does not rule out the other, given the presence of cattle in the early cities. Resistance to many other diseases could also have an urban basis (PAP).