An international team of scientists has sequenced the genomes of five Neanderthals who lived around 47,000 to 39,000 years ago (that is, late Neanderthals), and found that these individuals are all more closely related to the Neanderthals who contributed DNA to early modern humans than an approximately 120,000-year-old Neanderthal from Siberia (Altai Neanderthal).
Neanderthals in a cave. Image credit: Tyler B. Tretsven.
Scientists’ ability to retrieve DNA from a larger number of Neanderthals is still limited by poor preservation of endogenous DNA and contamination of Neanderthal skeletal remains.
Since 2010 whole genome sequences have been generated for four Neanderthal individuals from Croatia, Siberia and the Caucasus.
New methods for the removal of contaminating DNA from microbes and modern humans have now enabled researchers to sequence the genomes of five late Neanderthals.
“Our work demonstrates that the generation of genome sequences from a large number of archaic human individuals is now technically feasible, and opens the possibility to study Neanderthal populations across their temporal and geographical range,” said senior co-author Dr. Janet Kelso, from the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany.
Location and age of the five late Neanderthal specimens analyzed in this study (new), and other sites for which genome-wide data of Neanderthal samples have previously been published (old). Image credit: Hajdinjak et al, doi: 10.1038/nature26151.
For the study, Dr. Kelso and colleagues extracted DNA from Neanderthal specimens excavated from the Troisième caverne of Goyet (the specimen was dated to 43,000-42,080 years ago) and from Spy cave (39,150-37,880 years ago), both in Belgium, from Les Cottés cave in France (43,740-42,720 years ago), from Vindija cave in Croatia (more than 44,000 years ago), and from an archaeological site in the Caucasus (44,600-42,960 years ago).
“We see that the genetic similarity between these Neanderthals is well-correlated with their geographical location,” said study first author Dr. Mateja Hajdinjak, also from the Max Planck Institute for Evolutionary Anthropology.
“By comparing these genomes to the genome of an older Neanderthal from the Caucasus we show that Neanderthal populations seem to have moved and replaced each other towards the end of their history.”
The researchers also compared the new Neanderthal genomes to the genomes of people living today, and showed that all of the late Neanderthals were more similar to the Neanderthals who contributed DNA to present-day people living outside Africa than a much older Altai Neanderthal.
“We find that the bulk of Neanderthal gene flow into early modern humans originated from one or more source populations that diverged from the Neanderthals that were studied here at least 70,000 years ago, but after they split from a previously sequenced Altai Neanderthal around 150,000 years ago,” they explained.
Intriguingly, even though four of the Neanderthals lived at the time when modern humans had already arrived in Europe they do not carry detectable amounts of modern human DNA.
“Although four of the Neanderthals studied here post-date the putative arrival of early modern humans into Europe, we do not detect any recent gene flow from early modern humans in their ancestry,” the scientists said.
“It may be that gene flow was mostly unidirectional, from Neanderthals into modern humans,” said senior co-author Dr. Svante Pääbo, Director of the Max Planck Institute for Evolutionary Anthropology.
The team’s results are published in the journal Nature.
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Mateja Hajdinjak et al. Reconstructing the genetic history of late Neanderthals. Nature, published online March 21, 2018; doi: 10.1038/nature26151
