From Trees to Cities: Evolution Through Urbanization

Throughout history, there have been a myriad of situations or shocks, which have helped, pave the way for the evolution of modern Homo sapiens.  These include environmental changes; such as drought, an ice age, or volcanic eruption, the development of tools, larger brain size, and various others.  However there is one change that has developed fairly recently in terms of evolution that can be argued as having grand affects on human evolution: urbanization.  One major way in which city life has influenced human evolution is through diseases.   

Cities have long been a part of our culture.  Ever since the days when Catalhoyuk, Suberde, and Tepe Yahya joined Jericho's mesh of intercity trade, and four thousand years before the rise of the Sumerian cities of Ur, Uruk, and Kish, Stone Age metropolises from Anatolia to the edges of India were already rich in challenges and opportunities.  The emergence of these ancient cities has played an integral role in our evolution.  They brought our ancestors out of the caves and other isolated rural establishments they lived in, into densely populated cities.  Bringing all of these people together has influenced our evolution.  With people living close together in these metropolises, it allowed for diseases to be easily spread and much more common than before.  Researchers believe that this cesspool of diseases has allowed us as modern day humans, to evolve and adapt to become resistant to several infections.

Evolutionary biologist, Ian Barnes, has set out to prove this thinking.  In order to do this, he utilized the genetic variant, SLC11A1 1729+55del4 which is associated with the resistance of germs within cells (Charles Q. Choi).  To test this hypothesis, he and his team took DNA samples from 17 urban centers ranging from Catalhoyuk, 6000 B.C. or roughly 8,000 years old, to Juba which was erected in the 20^th century and is barely a hundred years old (Matt Kaplan).  One thing that he made sure of was to choose cities that had all been inhabited for different lengths of time.  In other words, a city settled for 200 years compared with one settled for 5,000.   In their findings, the team found that longer populated cities were more likely to have this variant than cities inhabited for only a hundred or so years.  The article specifically states the city of Susa in Iran.  This city has been inhabited for more than 5,200 years and the people here are “almost certain” to have this specific variant, which allows them to resist a number of diseases.  However, in comparison with Yakutsk in Siberia, which was only settled for a few hundred years, only around 70 percent of the people would have the variant (Charles Q. Choi).

According to the article by Charles Q. Choir, Barnes states that “The research shows evolution happening.”  Evolution takes more than a hundred years to take place so it makes complete sense that a population in a city that had been established for more than 5,000 years would have adapted to the conglomeration of diseases through acquiring this genetic variant.  Eventually, through natural selection, only those with this variant would survive.

Information is from: http://www.msnbc.msn.com/id/39345149/ns/technology_and_science-science

http://news.nationalgeographic.com/news/2010/11/101108-cities-immune-system-tuberculosis-tb-evolution-dna-genetics-science/