'Out of Africa' expansion has genetic sign

Anthropological and genetic records have illuminated the "Out of Africa" human expansion that occurred about 45,000 to 60,000 years ago, researchers say. As a small group of modern humans migrated out of Africa into Eurasia and the Americas their genetic diversity was substantially modified, geneticists at Stanford University report in the Proceedings of the National Academy of Sciences. However, genomic projects haven't fully taken into account the rich archaeological and anthropological data available, they said, and their review of both sides of the story provides a foundation that could lead to better understanding of ancient humans and, possibly, genomic and medical advances. "People are doing amazing genome sequencing, but they don't always understand human demographic history" that can help expand an investigation, review co-author Brenna Henn said. The anthropological information can help geneticists understand genetic changes that emerge over time, the researchers said. For example, geneticists have determined that genes for lactose intolerance and gluten sensitivity began to emerge in populations expanding into Europe around 10,000 years ago. Anthropology can help explain this, the researchers said; It was around this time that humans embraced agriculture, including milk and wheat production, and the populations that prospered -- passing on these mutations -- were those that embraced these unnatural food sources. This is an example of how human migrations drove a new form of natural selection, researchers Marcus Feldman said. "If you know something about the demographic history of populations, you may be able to learn something about the reasons why a group today has a certain genetic abnormality -- either good or bad," he said.