At first glance, it might seem like a bane to humanity to be living close together with the ability of germs and diseases to spread quickly. In the long run though we might be doing ourselves an evolutionary favor by living in cities.
For Scientific American's latest issue focusing on smart cities (check it out), Charles Q. Choi reports on research from the University of London that shows a link between disease resistance and populations that have lived in urban areas for a long period of time.
Evolutionary biologist Ian Barnes at the University of London and his colleagues focused on a genetic variant with the alphabet-soup name of SLC11A1 1729+55del4. This variant is linked with natural resistance to germs that dwell within cells, such as tuberculosis and leprosy.
The scientists analyzed DNA samples from 17 modern populations that had occupied their cities for various lengths of time. The cities ranged from Çatalhöyük in Turkey, settled in roughly 6000 B.C., to Juba in Sudan, settled in the 20th century.
The researchers discovered an apparently highly significant link between the occurrence of this genetic variant and the duration of urban settlement. People from a long-populated urban area often seemed better adapted to resisting these specific types of infections — for instance, those in areas settled for more than 5,200 years, such as Susa in Iran, were almost certain to possess this variant, while in cities settled for only a few hundred years, such as Yakutsk in Siberia, only 70 percent to 80 percent of people would have it.
Basically, populations that have lived in urban settings over generations are more likely to carry a genetic variant that helps them better resist disease - in this specific case that disease is tuberculosis. There are, however, some limitations to the study.
- "Populations get replaced frequently throughout history. This could mean the people they analyzed did not undergo the centuries or millennia of natural selection the researchers assumed they did to pass down this germ-resistant genetic variant."
- "Researchers might have problems with the dates for the founding of urban settlement used in his team’s study, which they arrived at by scanning archaeological and historical records."
That said, the researcher does not believe the limitation invalidate the findings.
Either way, it's an interesting idea: cities have the potential to not only green our world but positively affect human health in our immediate and evolutionary future.