The Long March of Human Genes -- Pasotti 2005 (309): 4 -- sciencenow:
In the new study, geneticist François Balloux and colleagues at the University of Cambridge show that geographic distance from Ethiopia (the place where the oldest human remains have been found) correlates with the genetic diversity of 51 present human populations distributed worldwide. The research gives support to the theory that, as humans left Africa, some versions of their genes became progressively lost over the migration routes. Thus, populations farther from Ethiopia are characterized by lower genetic variability.
The evolution of humans over the last 100,000 years.