New research led by the University of California, Berkeley reveals that beyond Neanderthals and Denisovans, humans interbred with two mysterious ‘ghost’ lineages: one in Africa more than 50,000 years ago, another in Eurasia over 1.7 million years ago.
Archaic hominins. Image credit: Ninara / CC BY 2.0.
With advancements in genomics, our understanding of human evolution is ever-evolving. Recent research from the University of California, Berkeley, has uncovered evidence that goes beyond the well-known interbreeding events with Neanderthals and Denisovans. This study suggests that modern humans mixed with two elusive ‘ghost’ lineages, hinting at an intricate tapestry of human ancestry.
Graduate student Yulin Zhang and colleagues emphasized the impact of Neanderthal and Denisovan genomics, which revealed that most non-Africans today possess about 1 to 2% Neanderthal ancestry, while Asians and Oceanians carry approximately 0.1 to 5% Denisovan ancestry. This genetic exchange hasn’t just faded into obscurity; it plays a significant role in shaping traits such as skin pigmentation and immunity.
However, this research also shines a light on a gap in our understanding. Despite the importance of archaic genomes in modern-day humans, only six high-coverage genomes have been sequenced so far—predominantly from Eurasia. Hence, the evolutionary history outside this region and earlier timelines remains a puzzle yet to be fully solved.
To delve deeper into these mysteries, the researchers used a novel computational approach called TRACE (TRacking Archaic Contributions via ARG Estimation). This method allows scientists to reconstruct genealogical relationships embedded in contemporary genomes, identifying DNA segments with ancient lineages, far older than previously recognized.
Upon applying the TRACE technique, Zhang and his team made a striking revelation: a ghost lineage that interbred with anatomically modern Homo sapiens in Africa over 50,000 years ago. This lineage diverged from our family tree approximately 800,000 years ago, coinciding with the divisions leading to Neanderthals and Denisovans. Now, its genetic traces account for about 1% of the genome in every living human, a finding that runs counter to previous assumptions about ghost ancestry being limited to African populations.
Interestingly, the second lineage, dubbed ‘super-archaic,’ dates back roughly 1.8 million years. While direct interbreeding with modern humans seems unlikely, this lineage appears to have had a genetic interaction with Denisovans in Eurasia. Later, when Denisovans mingled with modern humans, remnants of this super-archaic DNA were brought along, especially noticeable in Oceania’s populations that possess higher Denisovan ancestry.
This discovery of a super-archaic lineage, associated with a human lineage that lived over a million years ago without any sequenced DNA from that specific population, is particularly thrilling. Dr. Arjun Biddanda remarked on the significance of this finding, hinting at a profound connection to our deeper ancestry.
In summary, these two ghost lineages collectively contribute about 2% to the modern human genome. Zhang indicated that individuals today inherit approximately 0.5 to 1% of their genomes from this ghost lineage. The research suggests that these archaic segments cluster in areas related to immunity and metabolism, echoing the adaptive pressures faced by ancient humans as they navigated new environments and varying food sources.
Dr. Priya Moorjani noted that the patterns of adaptation align with the strongest selective pressures in human evolution throughout history, with interbreeding serving as a conduit for new genetic variation, essential for natural selection and evolutionary success.
Looking ahead, these researchers are excited about the potential for uncovering additional ghost lineages as genomic databases expand to include a diverse array of populations. Discovering more Denisovan genomes could also unearth further connections. Furthermore, newly sequenced protein sequences from Homo erectus fossils could eventually help pinpoint the identity of the super-archaic ancestor.
As researchers harness advanced computational methods to explore and reconstruct our genetic past, they are unlocking previously hidden narratives, shedding light on the complex tapestry that is human ancestry.
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Yulin Zhang et al. Recovering signatures of archaic hominin introgression using ancestral recombination graphs. Science, published online July 30, 2026; doi: 10.1126/science.aef8874