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Sequencing of Neanderthal Toe Bone Reveals Unknown Hominin Line

Roberta Estes

This week, in the journal Nature, scientists reported on the full sequencing of a Neanderthal toe bone found in the Denisova Cave in the Altai Mountains, the location where the Denisovan skeleton found in 2008 and sequenced earlier this year was also found.

The abstract of the paper, which is behind a paywall, says:

We present a high-quality genome sequence of a Neanderthal woman from Siberia. We show that her parents were related at the level of half-siblings and that mating among close relatives was common among her recent ancestors. We also sequenced the genome of a Neanderthal from the Caucasus to low coverage. An analysis of the relationships and population history of available archaic genomes and 25 present-day human genomes shows that several gene flow events occurred among Neanderthals, Denisovans and early modern humans, possibly including gene flow into Denisovans from an unknown archaic group. Thus, interbreeding, albeit of low magnitude, occurred among many hominin groups in the Late Pleistocene. In addition, the high-quality Neanderthal genome allows us to establish a definitive list of substitutions that became fixed in modern humans after their separation from the ancestors of Neanderthals and Denisovans.

The abstract also includes this graphic from the paper

This sequence is significant because of a number of unique findings.

  1. The skeleton showed physical traits of both Neanderthals and modern humans and is thought to be about 50,000 years old.
  2. Genetic sequencing revealed that this bone belonged to a Neanderthal woman, not a Denisovan, although other Denisovan remains, including one previously sequenced, have been found in this cave.
  3. The closest genetic relative is found in the Mezmaiskaya Cave in the Caucasus Mountains, some 2000+ miles distant.  Admittedly, we don’t have a lot of sequenced remains for comparison.
  4. Sequencing revealed a heretofore unknown genetic line of archaic humans.  This person obtained from between 2.7 to 5.8 percent of their genome from this unknown line. That percentage is equal to someplace between a great-great-great-grandparent and a great-great-great-great-great-grandparent, assuming only one ancestor was involved.  If this unknown human lineage was admixed into the population in multiple individuals, then the trace amounts could be passed around forever, just like the Neanderthal and Denisovan lineages are in Europeans today.
  5. This unknown line could be homo erectus.
  6. There is no evidence that this unknown human lineage interbred with either modern humans or Neanderthals.  I would presume this means that this unknown line then bred with the Denisovan group which did not manifest itself in contemporary humans.
  7. This individual was inbred with their parents being closely related, possibly half-siblings or an uncle and niece, or an aunt and nephew or a grandfather and granddaughter or grandmother and grandson.  Inbreeding was also common among the woman’s recent ancestors.  Another article headline this week pronounced that “Neanderthals Liked Incest” which I found to be offensive.  Incest is a highly negatively charged cultural word.  In the not so recent past, the practice of inbreeding was perfectly acceptable in European royalty.  Furthermore, we have no idea how these people felt about inbreeding, hence the word “liked” is misleading.  It could well be that they lived in a small nuclear family group and there were no other choices for partners.  There could also be other cultural and selection factors at play here of which we are unaware.  For example, perhaps males were more protective of mothers and children to whom they were related than ones where they had no family or group ties – increasing the likelihood of survival of offspring of women to whom the males were related.
  8. At least half of a percent of the Denisovan genome came from Neanderthals, but none of the Denisovan genome has yet been detected in Neanderthals.  If this holds, it would imply that our ancestors either bred with Neanderthals and Denisovans separately, or with Denisovans who carried Neanderthal DNA.  Given that most Europeans carry more Neanderthal DNA than Denisovan, the second scenario alone is unlikely.  It’s also possible that we simply haven’t found Neanderthal’s who did carry Denisovan DNA.
  9. More than 31,000 differences were found between modern humans and Neanderthals and Denisovans, many having to do with brain development.

Dienekes discussed this research in his blog as well.  Note his “family tree.”

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