The analysis of enamel proteins from six Homo erectus individuals in China, dating to around 400,000 years ago, has revealed the presence of Denisovan genes, indicating interbreeding between these distinct hominin groups. This finding, reported by Qiaomei Fu and colleagues in Nature, provides material evidence of deep historical connections within the human lineage.
The research focused on tooth enamel from five male and one female erectus individuals originating from Zhoukoudian, Hexian, and Sunjiadong in China. All six individuals exhibited two specific amino acid variants. One variant, A253G, had not been observed previously and appears to be unique to erectus, according to the researchers. Denisovans, Neanderthals, Homo antecessor from Atapuerca, great apes, and the so-called erectus from Dmanisi did not possess this A253G variant. The second variant, M273V, had been identified exclusively in Denisovans until its discovery in these Chinese erectus individuals. The presence of M273V in both Denisovans and these erectus individuals led to the conclusion that erectus and Denisovans met and interbred. This interbreeding produced a population in eastern Asia that retained the Denisovan genetic trait.
Historical Context of Hominin Migration
Homo erectus originated in Africa over 2 million years ago and subsequently spread across Eurasia, where it survived until just 107,000 years ago. The article notes that erectus passed through Israel during this migration, with Ubeidiya identified as a site from 1.9 million years ago linked to this movement. 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 that would produce Homo sapiens remained in Africa, while another branch migrated to Eurasia, giving rise to Neanderthals and Denisovans. Erectus originated in a migration 2 million years ago and encountered Denisovans, who emerged on another branch of the human tree in Asia less than a million years ago. Fossils identified by Chinese researchers as erectus date back as much as 2.1 million years. Remains found at Dmanisi in Georgia, dating to about 1.8 million years ago, have traditionally been described as erectus, though they may be considered a more archaic species or variant.
Interconnected Lineages
The research also highlights that Homo sapiens ancestors interbred with Denisovans, Neanderthals, and some other archaic hominin. It is suggested that at least some of the genes inherited by Homo sapiens from Denisovans may have originally come from Homo erectus. Some archaeologists propose that if all these variants on the Homo genus family tree were intermixing, they could technically be considered one species with a broad range of traits, though the article dismisses this as semantics.