Here’s what you’ll learn when you read this story:

• Researchers studying Denisovan ancestry within East Asian populations found an anomaly in the lineage of the Jomon people.
• The group has little to no Denisovan ancestry, showing that this lineage deviates from others in the region.
• Experts have two possible explanations to account for the unique Jomon ancestry.

Researchers recently found a rare, intriguing deviation in the lineage of what is now Japan’s ancient Jomon population—they were virtually devoid of any Denisovan ancestry (which is extremely common across Eurasian lineages). And in fact, according to the study published by the team on this discovery in in Current Biology,** they were the only East Asian lineage to lack significant DNA from the Denisovans. The discovery had researchers scratching their heads, theorizing how the Jomon people avoided something that all other strains of East Asian ancestry had in common.

“This implies different dispersals for modern humans into East Asia and suggests that Denisovans were sparsely distributed in the region,” the authors wrote.

In their attempt to develop a broad and deep understanding of the dispersal of ancient Denisovans over time, the team found “varying levels of Denisovan ancestry in Eurasians.” For instance, East Asian lineages had very high percentages of Denisovan DNA across the ages, while Western Eurasian lineages had very low percentages. But the Denisovans somehow missed intertwining with the Jomon people, who formed the basis of the modern population of one of East Asia’s biggest islands, almost entirely.

“Surprisingly, we found that individuals in the Japanese archipelago from the prehistoric Jomon period [from around 16,000 to 3,000 years ago] carried the least Denisovan ancestry among ancient and present-day East Asians,” the authors wrote.

The team has two competing theories as to why this may have occurred. Either the Jomon people partially descended from a separate lineage and only later engaged with an ancestry chain that included Denisovan DNA, or the addition of Denisovan ancestry came later in the development of that particular lineage (a period that the Jomon population could not have been a part of).

The team compiled ancient genomes from across Eurasia, and data indicated that many shared Denisovan DNA segments originated from a common episode of contact shared among East Asians. This compilation allowed researchers to use Denisovan ancestry to track population movement. But even though the Jomon population had the same origin as mainland populations, they lacked those distinctive Denisovan markers.

“This indicates that gene flow occurred from a source with less or no Denisovan ancestry and diluted the Denisovan ancestry of early East Asians,” Stephane Peyregne, co-supervisor of the study, said in a statement. “Denisovan DNA represents a powerful marker to reconstruct population history.”

Tim Newcomb is a journalist based in the Pacific Northwest. He covers stadiums, sneakers, gear, infrastructure, and more for a variety of publications, including Popular Mechanics. His favorite interviews have included sit-downs with Roger Federer in Switzerland, Kobe Bryant in Los Angeles, and Tinker Hatfield in Portland.