The “Out of Africa” expansion
Past Horizons, 01-11-2012
A new, comprehensive review of human anthropological and genetic records gives the most up-to-date story of the “Out of Africa” expansion that occurred about 45,000 to 60,000 years ago. This expansion, detailed by three Stanford geneticists Henn, Cavalli-Sforza, and Feldman presents an up-to-date version of the model. In the recent study is published in this edition of the Proceedings of the National Academy of Sciences they conclude it had a dramatic effect on human genetic diversity, which persists in present-day populations. As a small group of modern humans migrated out of Africa into Eurasia and the Americas, their genetic diversity was substantially reduced.
Previous genomic projects
In studying these migrations, genomic projects haven’t fully taken into account the rich archaeological and anthropological data available, and vice versa. This review integrates both sides of the story and 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 inform an investigation, said review co-author Brenna Henn, a postdoctoral fellow in genetics at the Stanford School of Medicine who has a PhD in anthropology from Stanford. “We wanted to write this as a primer on pre-human history for people who are not anthropologists.” “This model of the Out of Africa expansion provides the framework for testing other anthropological and genetic models,” Henn said “The basic notion is that all of these disciplines have to be considered simultaneously when thinking about movements of ancient populations,” said Marcus Feldman, a professor of biology at Stanford and the senior author of the paper. “What we’re proposing is a story that has potential to explain any of the fossil record that subsequently becomes available, and to be able to tell what was the size of the population in that place at that time.”
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.