Two mysterious ‘ghost’ lineages discovered in modern human DNA

Key Points:

• Researchers have identified two previously unknown ancestral human lineages, or “ghost” ancestors, by analyzing modern human genomes with a new method called TRACE, revealing missing branches in the human family tree.
• One lineage interbred directly with Homo sapiens in Africa over 50,000 years ago and contributes about 0.5% to 1% of DNA in modern humans, while the other, a “super-archaic” ancestor dating back 1.8 million years, passed DNA indirectly through Denisovans.
• These ghost lineages may correspond to Middle Pleistocene Homo populations like Homo heidelbergensis in Africa and possibly Homo erectus in Eurasia, although no direct DNA from these groups has yet been recovered.
• The findings deepen understanding of human evolutionary history, showing complex interbreeding events before migration out of Africa, and highlight the potential of genome-based genealogy reconstruction to uncover hidden ancestral contributions.
• Scientists hope TRACE will help identify more lost lineages in humans and other species, but emphasize that ancient fossil DNA remains crucial for confirming these genetic discoveries.