The human species originated in Africa and, over thousands of years, spread across the world and adapted to different surroundings, anthropologists have long agreed.

More disagreement surrounds precisely when and via what path people took, particularly to the Americas — which, along with Oceania, was one of the last two areas of the world to be settled.

A Kansas University professor co-authored a study, published this week in the journal Science, that provides an answer based on years of genomic sequencing.

Ancestors of present-day Native Americans came directly from Siberia, and they arrived here sometime in the last 23,000 years, said Michael Crawford, professor of anthropology and head of KU’s Laboratory of Biological Anthropology. While earlier studies hypothesized about a longer isolation period, the new study found the group spent no more than 8,000 years in Beringia, the land bridge that once connected Siberia to Alaska, and eventually split into northern and southern branches.

The study tested living and ancient Native Americans and Siberians, including the famous Kennewick Man, whose skeletal remains were found along the Columbia River in Washington in 1996.

Crawford said the study hinges on “coalescence analyses,” using not just one piece of DNA but the entire sequenced genome. That’s stronger evidence than so-called “morphological traits” such as head shape and the appearance of features, he said.

“One of the big breakthroughs is that the entire genome has been characterized for a number of ancient individuals, plus modern populations,” Crawford said.

“This study also pretty well does in the whole idea that gene flow from Europe contributed to the original migration of present-day Native Americans.”

Crawford was part of an international research team headed by the Center for GeoGenetics at the University of Copenhagen.

Each co-author’s years of previous research is an asset, he said, and no one individual would have the expertise to take on such a project alone.

“Having this very large consortium of researchers brings together people having very different backgrounds and training expertise,” Crawford said. “You’re talking in terms of gigantic data sets plus archeological material.”

The new study supports decades of research Crawford has done in the past, albeit with access to less precise technology.

He’s been researching the populating of the Americas since the mid-1970s and, in 1989, led the first foreign anthropological team into Siberia after the breakup of the Soviet Union. At that time — “pre-DNA days,” he said — he was studying primarily blood groups and proteins.

The study published in Science made international news this week. A separate study on the topic was published this week in the journal Nature, though it contained some different conclusions about migration to South America.

A Science article summarizes the two studies’ significance this way:

“Researchers agree that more genomes from modern and ancient Native Americans are needed to unravel the mysteries. For now, says anthropologist Jennifer Raff of the University of Texas, Austin, the two papers throw open an ‘incredibly exciting’ window on the ancestors of today’s Native Americans, as they sat poised to enter the New World.”