Two ‘Ghost’ Ancestors Hidden in Every Human Genome

The Two New Lineages

The TRACE method identified two distinct archaic populations that contributed DNA to modern humans:

1. The ‘Ghost’ Lineage (split ~800,000 years ago): This archaic hominin population split from the ancestors of modern humans roughly 800,000 years ago and contributed about 0.5% to 1% of the DNA found in every living human today . Crucially, this ghost lineage left traces in all present-day human populations, not just Eurasians or Africans—a truly global signal . The researchers have not yet named this population; it remains a statistical reconstruction from modern genomes, with no fossil or ancient DNA directly linked to it yet .

2. The ‘Super-Archaic’ Lineage (dating back ~1.8 million years): This deeply divergent hominin group is one of the oldest known to have interbred with later humans . Its DNA entered modern humans via Denisovans, who had already mixed with this super-archaic population before later breeding with Homo sapiens . Researchers suggest Homo erectus is a candidate for this group, but this remains unconfirmed .

How TRACE Works

TRACE (ancestral recombination graph method) was developed by Yulin Zhang at UC Berkeley and colleagues . Unlike previous methods that required reference DNA from ancient fossils or skeletons, TRACE detects archaic introgression in modern genomes without needing any ancient reference DNA . It does this by reconstructing family trees of each spot in a person's genome from contemporary DNA alone . The researchers analyzed 503 complete genomes from around the world .

Why It Matters

Many of the archaic DNA segments identified by TRACE are concentrated in genomic regions linked to immune function and metabolism, suggesting these introgressed variants may have been adaptive for modern humans . The study builds on earlier work that found hints of ghost admixture in African populations and prior evidence of a super-archaic population , but TRACE provides the most comprehensive global map yet .

A Caveat

Both lineages are statistical reconstructions from modern genomes; no fossil or ancient DNA has yet been directly linked to them . As paleoanthropologist John Hawks notes, every “ghost is a mathematical construct waiting for DNA from ancient skeletons to test whether it was real” . The search for physical evidence continues.