Geography predicts human genetic diversity

By analyzing the relationship between the geographic location of current human populations in relation to East Africa and the genetic variability within these populations, researchers have found new evidence for an African origin of modern humans.

The origin of modern humans is a topic that is hotly debated. A leading theory, known as “Recent African Origin” (RAO), postulates that the ancestors of all modern humans originated in East Africa, and that around 100,000 years ago some modern humans left the African continent and subsequently colonized the entire world, supplanting previously established hominids such as Neanderthals in Europe and Homo erectus in Asia.

In the new work reported this week, researchers Franck Prugnolle, Andrea Manica, and François Balloux of the University of Cambridge show that geographic distance from East Africa along ancient colonization routes is an excellent predictor for the genetic diversity of present human populations, with those farther from Ethiopia being characterized by lower genetic variability. This result implies that information regarding the geographic coordinates of present populations alone is sufficient for predicting their genetic diversity. This finding adds compelling evidence for the RAO model. Such a relationship between location and genetic diversity is indeed only compatible with an African origin of modern humans and subsequent spread throughout the world, accompanied by a progressive loss of neutral genetic diversity as new areas were colonized. The loss of genetic diversity along colonization routes is smooth, with no obvious genetic discontinuity, thus suggesting that humans cannot be accurately classified in discrete ethnic groups or races on a genetic basis.