Neanderthal DNA found in an inch-long toe bone that dates back 50,000 years indicates that Neanderthals might have died out due to interbreeding and incest with closely related family members.
The Neanderthal toe bone, of a female, was discovered in a Siberian cave. At that time, Neanderthals and other early humans often shared the same territory, and possibly interbred until those species eventually died out.
A team of scientists worked to sequence the DNA from the toe bone. After they compared the DNA with that of modern-day humans, and with a group of Neanderthals called Denisovans, their analysis determined that Neanderthal DNA could be found in around two percent of modern people who did not live in Africa.
Denisovan DNA was only found in approximately a half of one percent of modern-day humans, with Native American people and Asians comprising 0.2 percent of the overall total.The study was published in the journal Nature.
A fourth, as yet unknown, hominid contributed even more DNA to the Denisovan genome — about six percent. Denisovans weren’t recognized as a distinct type of early hominid until 2010.
According to geneticist Kay Prufer, of the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, the unknown DNA might be from Homo erectus, though it’s impossible to know for sure, until further studies are performed.
Though the Neanderthal toe bone is small, the DNA within it has aided greatly in fleshing out how different ancestors of modern-day humans interacted around 12,000 – 126,000 years ago.
The researchers who extracted the Neanderthal DNA from the toe bone were able to tell by the genomes that the female’s parents were related. According to the study, the researchers learned that the female Neanderthal’s parents possibly “Had a mother in common, [or were] double first cousins,” or related in some other very close way, such as being “a grandfather and a granddaughter, or a grandmother and a grandson.”
For the Neanderthal species to continue on at all, if the population was already in decline, the researchers suggest that these early ancestors of modern-day men might have had no choice but to interbred with each other.
According to one of the researchers, biologist Montgomery Slatkin, the data they got from the DNA indicates that the population of the Neanderthals at the time was small, and that “breeding among relatives was reasonably common.” However, more studies are necessary before a definitive statement can be made as to the extent that interbreeding occurred and was partially behind the Neanderthals dying out.
The team of researchers who wrote the study believe that ancestors of Denisavons and Neanderthals split and were not a part of the lineage that resulted in modern-day humans. This split, the researchers theorize, happened about 600,00 years ago. Then, around 400,000 years ago, the two groups split from each other.
According to the researchers and their analysis of the genomes taken from the Neanderthal toe bone, the populations of both Denisovans and Neanderthals were decreasing as long as 1 million years ago. At the same time, the populations of ancient human ancestors that led directly toward modern-day humans increased. The DNA findings, the researchers concluded, probably means that around 30,000 years ago, Homo sapiens became the only type of humans to survive.
That might seem to be a lot to surmise from the DNA in one Neanderthal toe bone, but the genomes present in the toe bone indicates that interbreeding and incest definitely occurred between the human species and within individual species, such as the Neanderthals.
According to Svante Paabo, senior author of the study and director of the Max Planck Institute’s department of genetics, the amount of DNA sequences that distinguishes modern-day humans from Neanderthals is fairly short.
Another of the study’s authors, David Reich — a professor of genetics at Harvard Medical School in Boston — suggests that the interbreeding and incest which occurred among the declining populations of Denisovans and Neanderthals might have made the remaining members of the species less fit, another possible cause of their becoming extinct.
It is generally believed by scientists that as recently as 30,000 years ago, Neanderthals lived in Europe, though their populations were in decline. This period of time overlaps when other species of ancient hominids inhabited Europe, including the Denisovans and Homo erectus.
The DNA discovered in the Neanderthal toe bone proves that interbreeding and incest occurred within the dwindling Neanderthal community and potentially with other species of ancient humans.
Though more studies need to be done to confirm just how wide-spread this interbreeding was, the DNA evidence in the Neanderthal toe bone suggests that Neanderthals and other early human ancestors contributed to their own demise through interbreeding and incest.
Written by: Douglas Cobb