Up to one-fifth of the genome of modern humans may originate from unknown ancient hominins that diverged from our evolutionary line more than a million years ago. This unexpected conclusion was reached by geneticists from the University of Utah. Their work has been published as a preprint on the bioRxiv platform.

What the Genetic Analyses Showed
The scientists carefully examined the distribution of genetic variants in modern humans, Neanderthals, and Denisovans. This made it possible to reconstruct ancient episodes of interbreeding between different hominin lineages.

The result proved striking: according to the researchers’ estimates, about 19.6% of the Homo sapiens genome was inherited from a so-called “super-archaic” population. These ancient hominins diverged from the line of modern humans around 1.3 million years ago. By comparison, only about 2% of our DNA comes from Neanderthals.

Two Distinct Super-Archaic Populations
The analysis indicated that at least two separate super-archaic groups were involved in ancient hybridization events. One of them likely interbred with the ancestors of modern humans in Africa, while the other interbred with the ancestors of Neanderthals and Denisovans in Eurasia.

This discovery significantly complicates the picture of human evolution. Rather than a relatively straightforward line of development, modern humans emerge as a genetic mosaic assembled from contributions of multiple ancient populations.

A Possible Candidate — Homo erectus
The researchers cautiously suggested that one of the most likely candidates for this “mysterious” ancestor is Homo erectus. This species left Africa about two million years ago and spread widely across Eurasia long before the appearance of Neanderthals and Denisovans.

However, the authors emphasized that it is not yet possible to determine exactly which hominin species contributed such a substantial share of genes. Additional genetic data and new paleoanthropological discoveries will be required for definitive conclusions.

In Brief
Geneticists from the University of Utah have found that about 19.6% of the modern human genome originates from two unknown “super-archaic” populations of ancient hominins that split from our lineage more than 1.3 million years ago. One group interbred with the ancestors of Homo sapiens in Africa, while the other interbred with the ancestors of Neanderthals and Denisovans in Eurasia. This greatly exceeds the contribution of Neanderthals (only about 2%) and turns human evolutionary history into a complex genetic mosaic. One possible source is Homo erectus, but precise identification remains impossible for now. The work has been published on bioRxiv.