There are traces of ghost ancestors in human DNA .

Scientists have identified traces of long-lost human ancestors embedded within the modern human genome, revealing a more complex evolutionary history than previously understood. The discovery, published in Science, was made by researchers at the University of California, Berkeley, using a new computational method called Trace (TRacking Archaic Contributions via ARG Estimation). This technique allows scientists to detect genetic contributions from ancient hominins without relying on reference genomes from extinct species, simply by analyzing complete modern human genomes. The study found evidence of interbreeding between modern humans and unknown archaic groups that existed before Homo sapiens migrated out of Africa. One such ancestor, referred to as a “ghost” lineage, crossed with early humans over 50,000 years ago, long before the most recent migration of Homo sapiens into Europe and Asia. These genetic traces make up approximately 1% of the modern human genome, comparable to the percentage of Neanderthal DNA present today. This suggests that these mysterious ancestors were part of a broader network of human evolution, with their genetic legacy surviving through interbreeding events. The research team also uncovered that inhabitants of Oceania inherited genetic material from an even older, “super-archaic” lineage, indirectly through Denisovians. This finding is particularly exciting because it indicates that genetic contributions came from a human population that lived over one million years ago, despite the absence of direct DNA sequences from that group. Arjun Biddanda, a co-first author of the study, emphasized how this discovery highlights the depth and complexity of our shared evolutionary past. To validate their findings, the researchers used simulations to test the accuracy of the Trace method before applying it to high-coverage genomes from diverse populations around the world, including data from the 1000 Genomes Project. Their approach enabled them to trace genetic contributions from multiple archaic human groups, uncovering episodes of interbreeding that had remained hidden until now. These results challenge previous assumptions about the linear nature of human evolution and suggest instead a web-like pattern of interactions among different hominin species. The implications of this work extend beyond understanding human ancestry. By identifying genetic markers linked to these ancient lineages, scientists can gain insights into traits that may have been influenced by these distant relatives. For example, some genes associated with immune function and skin pigmentation show signs of selection pressure, possibly due to environmental adaptations shared with archaic hominins. Such discoveries could help explain variations in disease susceptibility and other biological characteristics among modern human populations. Looking ahead, the Trace method opens new avenues for exploring the genetic legacies of other extinct hominin groups. Researchers plan to apply this tool to additional datasets, potentially uncovering more instances of interbreeding and refining the timeline of human evolution. As more data becomes available, the picture of our ancestral past will continue to evolve, shedding light on the intricate connections that shaped the human species.