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Neanderthals v. Denisovans

As my loyal readers know by now, I am a sucker for "add-on" genetic reports. The latest that I took was an "Archaic" report offered by My Living DNA, teasing that: "Our Archaic DNA test allows you to explore how much of your DNA is attributed to Neanderthal and Denisovan humans." I was hooked! Here is what I discovered from the results.

To start with, my Neanderthal score was 285, which matched my Neanderthal score from the 23andMe test I took previously and discussed in my blog (click here for the link to that post). One statement that stood out about my results was this: "Typically, scores between 250 to 400 likely for someone without African ancestry." I reached out to LivingDNA for clarification since I thought everyone's common ancestors originated from Africa. They responded extremely quickly: "Where we have referred to African Ancestry in this instance it is the Autosomal results which is the most recent 8 to 10 generations." My most similar Neanderthal remnants were "Mezmaiskaya 1 Neanderthal." The Mezmaiskaya Cave is located in the Azish-Tau Ridge in the Northwestern foothills of the North Caucasus mountains, the Republic of Adygea, Russia. The two Neanderthal samples in their database had been radiocarbon dated to around 65,000 and 43,000 years ago.

As for my Denisovan score, it was 132 (Denisovan scores range between 0 and 1,634. Typically, the maximum score one might expect to see is 400). Since I had focused on Neanderthals before, I will talk more about the Denisovans (Homo denisova / H. altaiensis). They are an extinct species or subspecies of archaic humans that are believed to have lived across the landmass of Asia, the Philippines, and New Guinea. They may have also reached further into Australasia, but this has yet to be confirmed. Denisovans are believed to have split from the Neanderthal lineage soon after their common ancestor separated from the modern human lineage more than 390,000 years ago; the oldest Denisovan remains have been dated to 200,000 years. Denisovans are named named after a Russian hermit, Denis, who in the 18th century lived in a cave where Denisovan remains were later discovered. The cave's cool climate helped preserve the DNA.

Currently, far less is known about Denisovans compared to Neanderthals. The number of and quality of Denisovan remains is far lower, with positive identifications limited to only a handful of caves. In fact, the first identification of a Denisovan individual only occurred in 2010.

While no complete skull of a Denisovan has yet been found, the analysis of their DNA, along with the few bone fragments and teeth that have been identified, has allowed scientists to estimate their physical appearance and a significant part of their population history. Much like Neanderthals, Denisovans are thought to have had a long, broad, and projecting face with a sloping forehead. Though their nose may have been larger and their jaw more protruding when compared to Neanderthals. They also are thought to have had dark skin, eyes and hair.

In March 2010, scientists announced the discovery of a finger bone fragment of a juvenile female who lived about 41,000 years ago. Analysis of the bone showed they are from a 13-year-old girl who was born to a Neanderthal mother and a Denisovan father; her DNA was found to be 40% Denisovan and 40% Neanderthal. She was nicknamed Denny. To discover a first-generation person of mixed ancestry was extraordinary. But there were more revelations to come. Further detailed studies of the genes of Denny’s Denisovan father were found to contain fragments of Neanderthal DNA. These indicated that interbreeding between the two species had also occurred at an earlier time.

At first sight, Denny’s remarkable ancestry suggests that Neanderthals and Denisovans must have mated with each other regularly. However, one of the scientists noted: "The DNA of Neanderthals and Denisovans are distinct. We can easily tell them apart. That argues against frequent interbreeding. Otherwise they would have ended up with the same DNA."

An artist's rendering of "Denny"

But why at Denisova? One suggestion is that the cave represents a border outpost for both species, one that was situated at the very eastern edge of the range of the Neanderthals, who were primarily a European species, and at the very western tip of the homelands of the Denisovans, who were an eastern species. Occasionally members from both groups would have reached the cave at the same time – with amorous consequences.

The global distribution of Denisovans has for the most part been estimated through the proportion of Denisovan DNA found in modern humans alive today. Analysis suggests that the last time Denisovan DNA entered the modern human gene pool was as recent as 50,000 years ago. This analysis also suggests that Denisovans may have gone extinct as little as 15,000 years ago.

As in the case of Neanderthals, archaic introgression has had a role in shaping the modern human genome and its adaptation to the environment. Interestingly, DNA evidence suggests that Denisovan DNA may have aided modern humans in adapting to life at high altitudes. A variant of the gene has been linked with an improvement in coping with low oxygen levels. This variant came from ancestors of the Nepalese Sherpa people and spread rapidly through the populations of the Tibetan Plateau approximately 30,000 years ago, suggesting that this variant is highly beneficial to survival.

In humans who live today, around 2 percent of DNA in non-Africans comes from Neanderthals. Denisovan DNA remnants are commonly found in aboriginal Australians and people in Papua New Guinea. Traces have also been found among Asians and native Americans.

The genetic contribution from the Neanderthal to the present-day human gene pool can be found in all human populations outside of Africa, whereas the contribution from Denisovans is found exclusively in Asia and Oceania. It is thought that their DNA helped modern humans adapt to the different local environments that they encountered as they spread across the Eurasian landmass, and beyond.

So how does this fit in with my overall DNA? Maybe those genes made that way back West when Genghis Khan and the Mongol Empire in the 13th century. On 9 April 1241, Mongol detachments entered Meissen (a medieval principality in the area of the modern German state of Saxony) following a decisive Mongol victory at the Battle of Liegnitz in Poland. The Mongol light reconnaissance units, led by Orda Khan, pillaged through Meissen and burned most of the city to the ground. The subjugation of Hungary also opened a pathway for the Mongol Horde to invade Vienna. Afterall, according to my results from 23andMe, I have 0.5% trace ancestry from Northern Indian & Pakistani DNA (0.4%) and Peninsular Arab DNA (0.1%). That might possibly explain how Asian DNA made its way West and contribute to my overall results. Another thought is that it could have been carried via the Silk Road, but that is a story for another time. Gotta love these add-on tests!


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