Analysis of ancient teeth reveals that Homo erectus individuals in China, dating back around 400,000 years, possessed Denisovan genes, indicating a significant interbreeding event that altered the genetic composition of these early human populations. This finding, reported on Wednesday in Nature by Qiaomei Fu and colleagues, suggests a profound genetic intermixture between distinct hominin groups in eastern Asia.
The research focused on tooth enamel from six Homo erectus individuals—five male and one female—excavated from sites including Zhoukoudian, Hexian, and Sunjiadong in China. All six individuals exhibited two specific amino acid variants. One variant, A253G, was previously unknown and appeared unique to Homo erectus, not found in Denisovans, Neanderthals, Homo antecessor from Atapuerca, Spain, great apes, or the Homo erectus from Dmanisi.
However, the second variant, M273V, had been exclusively identified in Denisovans until now, and its presence in these Chinese Homo erectus individuals confirms a shared genetic trait. The conclusion drawn by the researchers is that Homo erectus and Denisovans met and interbred, resulting in a population in eastern Asia that subsequently retained the Denisovan genetic characteristic. This genetic exchange represents a blurring of distinct hominin lineages.
Genetic Blurring of Ancient Peoples
Homo erectus, a lineage that emerged in Africa over 2 million years ago, undertook extensive migrations, spreading across Eurasia and surviving until just 107,000 years ago. This ancient migration path included passage through regions like Israel, with Ubeidiya identified as a site from 1.9 million years ago linked to this early movement. The distinct genetic makeup of these migrating populations was subject to alteration upon encountering other groups.
In contrast, Neanderthals, Homo sapiens, and Denisovans are understood to have arisen from a separate branch in Africa that split off the hominin tree perhaps around 800,000 years ago. The branch destined to produce Homo sapiens remained within Africa, while another branch migrated to Eurasia, giving rise to Neanderthals and Denisovans in those territories. This established distinct geographical and genetic trajectories for different hominin groups.
The encounter between Homo erectus, originating from a migration 2 million years ago, and Denisovans, who emerged on another branch of the human tree in Asia less than a million years ago, highlights a pattern of intermixture. Fossils identified by Chinese paleontologists as Homo erectus date back as much as 2.1 million years, underscoring the long presence of this lineage before the documented genetic exchange.
A Legacy of Intermixture
Some archaeologists suggest that if all these variants on the Homo genus family tree were mixing and mating, they were technically all one species with a very wide range of traits, though the article dismisses this as semantics. This perspective, however, underscores the historical reality of genetic boundaries being permeable. Remains found at Dmanisi in Georgia, dating to about 1.8 million years ago, traditionally described as Homo erectus, might also be considered a more archaic species or variant, further complicating the picture of distinct ancient populations.
The historical record of genetic intermixture is not limited to these ancient groups. Our own Homo sapiens ancestors also mixed with Denisovans, Neanderthals, and other archaic hominins. This continuous pattern of genetic exchange across distinct groups has shaped the genetic landscape of humanity. The research further notes that at least some of the genes inherited by Homo sapiens from Denisovans may have originated even earlier in Homo erectus, indicating a complex, multi-generational legacy of genetic flow between disparate populations. This ongoing process of genetic absorption and re-distribution fundamentally alters the distinct genetic identities of populations over deep time.