Study Reveals Extensive Genetic Exchange Between Early Humans and Neanderthals

Recent research led by geneticists and artificial intelligence experts has revealed that early humans and Neanderthals were more interconnected than previously believed, with repeated episodes of genetic exchange spanning nearly 200,000 years. The study, published in Science and led by Joshua Akey of Princeton University, utilized a new machine learning tool called IBDmix to analyze DNA from 2,000 present-day humans, three Neanderthals, and one Denisovan.

Liming Li, a professor at Southeast University in Nanjing, China, who contributed to the study, explained that this is the first time multiple waves of modern human–Neanderthal admixture have been identified. According to the research, early humans and Neanderthals branched off around 600,000 years ago, but began interacting and exchanging genes as early as 250,000 years ago. Akey stated, "For about 200,000 years, modern humans interacted with Neanderthal populations," leaving lasting genetic traces.

The analysis identified three major periods of contact: 200,000–250,000 years ago, 100,000–120,000 years ago, and the most significant around 50,000–60,000 years ago. These findings challenge earlier models that suggested modern humans remained in Africa until a single dispersal event about 50,000 years ago. Akey noted, "Our models show that shortly after modern humans arose, they migrated out of and back into Africa," indicating more frequent movement and contact with Neanderthals and Denisovans than previously recognized.

The study also found that Neanderthal populations were smaller than earlier estimates, revising the number of breeding individuals from about 3,400 to 2,400. Much of the genetic diversity previously attributed to Neanderthals was actually due to gene flow from modern humans. The research supports the assimilation model, first proposed by anthropologist Fred Smith, suggesting that Neanderthals were gradually absorbed into modern human populations rather than going extinct in a single event. Akey commented, "Neanderthals were likely on the brink of extinction for a long time," and described modern humans as "waves eroding a beach, steadily overwhelming Neanderthals and incorporating them into our populations."

These findings provide new insight into the complexity of human evolution, highlighting extensive migration, interaction, and cultural exchange between early humans, Neanderthals, and Denisovans.