The Neanderthal had a feature which was unique to them (they ALL had it) and is found in some modern humans: the retromolar gap or retromolar space.
A paper published in March 2015, "The Retromolar Space: A Morphological Curiosity Observed Amongst the Protohistoric Arikara and Mandan" by C. de la Cova DOI: 10.1002/oa.2451 International Journal of Osteoarchaeology, noted that it is quite frequent among two American Native groups, the Arikara and the Mandan peoples:
The retromolar space (RMS), defined in paleoanthropology as a space posterior to the third molar, between the distal edge of the tooth and the anterior margin of the ascending ramus when the mandible is held in lateral view, has been described as an autapomorphic trait unique to Neandertals despite its presence in anatomically modern humans (AMHs). This study examined RMS prevalence in a sample of Protohistoric Arikara and Mandan Amerindians to determine what craniofacial morphology is correlated with the RMS. It was hypothesized that the feature would be present in the Amerindians studied and associated with a long cranial length, a large nasal height, midfacial prognathism, a broad mandible, and dental wear. The results indicated that RMSs were present in the Arikara and Mandan and significantly correlated with cranial length, cranial breadth, nasal height, bizygomatic breadth, basion-nasion length, basion-nasiospinale, mandible length, gonial angle, bigonial breadth, and dental wear. Thus, RMSs are associated with a dolichocephalic skull, wide cranial and facial breadth, a prognathic face, large nose, and a corresponding wide and long mandible with a reduced gonial angle. This suggests that the RMS is the result of these features merging together in the craniofacial complex and should not be considered a Neandertal autapomorph.
Of course, the conclusion that Ms. Cova reaches is that it is not an exclusive Neandertal feature but that it is related to a certain skull morphology that these natives have...
How about testing another hypothesis: the natives have it because they have a high admixture with Neandertals and got the genes that produce the retromolar gap from the Neandertals themselves... maybe even admixing in America and not in Asia before migrating to the New World.
Both Mandan and Arikara live in North Dakota, and some websites and some books too, suggest that they have some link to the Welsh! example below:
Several explorers claimed that the Mandans were white people; that the skin on their bodies was white and that the copper color was applied to the exposed parts. Verendrye even claimed that they were a mixture of white and black races. Volney, who was among them at a very early date, says that the children are born white like the Europeans and that the women were white upon the thighs, hips and lower parts of the body and says that it is wholly erroneous to suppose that the copper color is natural to them.
These travelers all make mention of many of the Mandans having blue eyes and red hair. Maximillion of Wied, a German traveler-scientist and linguist, and who lived with the Fort Clark Mandan villagers during the winter of 1833-34, tabulated a list of Mandan words and called attention to a very marked resemblance to the Welsh tongue...
Below: A Neandrtal skull and the "gap" behind the last molar.
The text above is from a very interesting site on the Mandans, based on the work of A.B. Welch which was written in the 1920s. Was the "white" "red hair" a Neandertal trait and not a Welsh one?
also tells about a Mandan who retold the ancient story of his people: An Indian tells Welch a story about meeting a "white man" who lived in the ground (cave dweller?) when they migrated to their current territory...
The text on these Indians, from "Travels in the Interior of North America" (1843) by Maximilian Wied (Prinz von) can be read here: (Link).
I definitively do not support the idea of a Welsh migration to America, or even the possibility that these were Vikings who admixed with the natives. Probably from time to time a group of Vikings or even cod fishermen from Medieval Europe were castaways on the coasts of America, but they could have never been enough of them to have such an impact as the one hinted at by Welch or Wied. A stable pre-existing population of Neandertal people would be another story and admixture would have had interesting consequences.
Further reading: Footprints of the Welsh Indians: Settlers in North America Before 1492, William L. Traxel Algora Publishing, 2004.
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