Ghost Ancestor's Genome Hides Across Human DNA
SkimNews Take
That the ghost ancestor's DNA is uniformly scattered across modern genomes is precisely what enables full reconstruction — suggesting similar computational sweeps could systematically surface more hidden lineages with no fossil trail.
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- Yulin Zhang and colleagues at the University of California, Berkeley found that 0.5 to 1 percent of any modern human's DNA comes from an unidentified 'ghost ancestor,' with fragments distributed evenly enough across nearly the entire genome to potentially reassemble the extinct lineage's near-complete genome.
- Priya Moorjani, also at Berkeley, said the team built a 'family tree' for parts of the genome — newly feasible computationally — and validated it by correctly identifying Neanderthal and Denisovan DNA from modern genomes alone before turning it on the ghost lineages.
- The more recent ghost ancestor split from the human family tree roughly 800,000 years ago, then reconnected and interbred with Homo sapiens, most likely in Africa — the researchers speculate it could be Homo heidelbergensis, a species with fossils in Africa as recent as 300,000 years ago.
- A second 'super-archaic' ghost ancestor split from the human lineage about 1.8 million years ago and later interbred with Denisovans in Eurasia; Chris Stringer at London's Natural History Museum, who called the study 'important and innovative,' identifies the likely candidate as Homo erectus.
- Neanderthal and Denisovan DNA survives only in patches — long segments of modern genomes have almost none — because their small populations carried more detrimental mutations that selection weeded out, whereas the ghost ancestor's larger population meant its DNA was more likely neutral and endured, the team explains.
- The findings, published in Science (DOI: 10.1126/science.aef8874), give researchers a way to recover genetic information about extinct human relatives known only from fossils, without ever finding their ancient DNA.
Why it matters: For evolutionary biology, this is the first practical way to recover genomic data from human ancestors known only from fossils — like Homo heidelbergensis and Homo erectus — by piecing together the DNA their descendants still carry. Moorjani called it 'the next frontier of research in human genetics,' because it works without any ancient DNA samples at all.
