Blast from the Past

David Reich

Geneticist David Reich

The ability to extract and then sequence ancient DNA, not just from ancient human bones, but also from the bones of our ancient cousins the Neanderthals, is upending old notions of human migration and history.

The latest in a rapid succession of new findings suggests that intermixing between Neanderthals and early modern humans happened earlier than we once thought – about 100,000 years ago versus 50,000 years ago – at a time that challenges long held theories about when humans migrated out of Africa and how far those migrations took them. And by looking at DNA sequences extracted from several different Neanderthal bones, researchers discovered that the gene flow didn’t just go from Neanderthals to humans.

This latest finding illustrates the impact DNA data, specifically data from ancient DNA, has had. Svante Paabo of the Max Planck Institute for Evolutionary Anthropology pioneered this innovation for extracting ancient DNA and accurately sequencing, and it radically transformed our understanding of human history.Harvard population geneticist David Reich puts this new innovation into context in a long interview he did with The Edge. Reich, who studies genetic variation among human populations, said that scientists have gained great new insights into history by comparing ancient DNA sequences to present-day humans’ genetic data.

“It’s a radically new type of information about the past; it’s a great gift to be able to have access to it,” Reich said in the interview. “It’s a great surprise. Who would have thought DNA survived that long?”

Probably the most profound insight from looking at ancient DNA and making comparisons with data from modern humans is that all human populations today are mixed. This isn’t just about mixing between humans and Neanderthals, but mixing among early human populations and that data offers great insight into human history. He’s also looked at non-ancient human DNA to garner similar insights. So for example, Reich has looked at populations in India where they found that populations mixed there between 2000 to 4000 years ago. Before that there were unmixed populations.

“Amazingly, what you could see from the genetic data was an event in which you could see cultural change,” he said.

You can see something similar in more recent history by looking at the DNA of African Americans, which includes European ancestry, a clear mark of the slavery in the United States.

“What you’re seeing in the imprint of these populations genetically is the history of power inequality, which is usually males of power from one group having preferential access to local females, and that’s what you see in these groups,” Reich said.Listen to Reich’s interview below.

The Edge Foundation, also has a video of his interview on its site here.