Berkeley Tool Finds 'Ghost' and 'Super-Archaic' DNA in Modern Humans

Researchers at UC Berkeley have identified genetic traces of two previously unknown extinct human relatives within the genomes of all modern humans. Using a new computational method, the team discovered a "ghost ancestor" that interbred with Homo sapiens in Africa more than 50,000 years ago, as well as "super-archaic" DNA from a lineage dating back 1.8 million years.

The discovery was made possible by a technique called TRACE (TRacking Archaic Contributions via ARG Estimation). Unlike traditional paleo-genetics, which requires the sequencing of physical fossils, TRACE utilizes Ancestral Recombination Graphs (ARG) to reconstruct genealogical connections using only present-day human genomes. This approach revealed that the ghost lineage split from modern human ancestors approximately 800,000 years ago and now contributes between 0.5% and 1% of the modern human genome. Additionally, the team found that the 1.8-million-year-old super-archaic DNA entered the human genome indirectly after first interbreeding with Denisovans in Eurasia.

A Shift Toward a Genomic Web

For years, the scientific community has documented interbreeding between modern humans, Neanderthals, and Denisovans, but these findings relied heavily on the availability of rare ancient DNA samples. The existence of "ghost populations"—extinct groups that left a genetic mark but no sequenced fossils—had been hypothesized but remained difficult to map. The TRACE method changes this by allowing scientists to detect these hidden lineages directly from living populations. Notably, the ghost ancestry was detected even in genomic regions previously thought to be intolerant of Neanderthal and Denisovan ancestry.

Implications for Human Adaptation

This research fundamentally alters the conceptual model of human evolution. Priya Moorjani, a Berkeley associate professor of molecular and cell biology, notes that while evolution is often viewed as a branching tree, new data reveals a "complex web of populations connected by repeated episodes of migration and mixing."

These genetic contributions were not random; archaic DNA segments are notably concentrated in genomic regions related to immune defenses and metabolism. This suggests that interbreeding provided critical raw genetic material for natural selection, potentially helping early humans adapt to new environments and pathogens. Arjun Biddanda, a postdoctoral researcher at Johns Hopkins University, highlighted the significance of the super-archaic finding, noting it reveals contributions from a lineage that lived over a million years ago despite the total absence of sequenced DNA from that population.

The Future of Ancestry Mapping

Beyond human evolution, the development of the TRACE tool provides a blueprint for discovering extinct species across the broader tree of life without requiring physical remains. As researchers continue to apply this method, the focus will shift toward identifying other hidden lineages and determining exactly how these ancient genetic fragments continue to influence modern human health and biology.