Stanford researchers have completed a new analysis of the anthropological and genetic history of humans' migration out of Africa. The account, which appears in the Proceedings of the National Academy of Sciences, is the most up-to-date story of the "Out of Africa" expansion that occurred approximately 45,000 to 60,000 years ago.
The anthropological information can inform geneticists when they investigate certain genetic changes that emerge over time. For example, geneticists have found that genes for lactose intolerance and gluten sensitivity began to emerge in populations expanding into Europe around 10,000 years ago.
The anthropological record helps explain this: It was around this time that humans embraced agriculture, including milk and wheat production. The populations that prospered – and thus those who survived to pass on these mutations – were those who embraced these unnatural food sources. This, said Feldman, is an example of how human movements drove a new form of natural selection.
Populations that expand from a small founding group can also exhibit reduced genetic diversity – known as a "bottleneck" – a classic example being the Ashkenazi Jewish population, which has a fairly large number of genetic diseases that can be attributed to its small number of founders. When this small group moved from the Rhineland to Eastern Europe, reproduction occurred mainly within the group, eventually leading to situations in which mothers and fathers were related. This meant that offspring often received the same deleterious gene from each parent and, as this process continued, ultimately resulted in a population in which certain diseases and cancers are more prevalent.
Previously: NIH introduces online genetics course for social and behavioral scientists, Roots of disease may vary with ancestry, according to Stanford geneticist and Mexican-American, African-American genomes sequenced
Photo by Guy Tear, Wellcome Images