Why did someone with the Lewis and Clark expedition report that the Mandans spoke with Welsh words? I read they mostly died of an epidemic. Do any remain to be compared with Welsh DNA?
George Catlin documented that, iirc. Most of the Mandan died of an epidemic, but the tribe continues on the Three Affiliated Tribes reservation in the vicinity of Newtown, ND.
Given the lack of a writing system (the only pre-Roman inscriptions in Iberia are, in order, Greek, and distantly behind that are some Phoenician, so-called Tartessian, and various Celtic oghams) or surviving inscriptions, I've never seen any real evidence (plenty of chimerical stuff on the web though) that the Basques were in Iberia prior to the Romans.
Population Rh(D) Neg Rh(D) Pos Rh(D) Neg alleles Basque people 21-36%[13] 65% approx 60% Native Americans approx 1% 99% approx 10% America B.C.A fascinating letter I received from a Shoshone Indian who had been traveling in the Basque country of Spain tells of his recognition of Shoshone words over there, including his own name, whose Shoshone meaning proved to match the meaning attached to a similar word by the modern Basques. Unfortunately I mislaid this interesting letter. If the Shoshone scholar who wrote to me should chance to see these words I hope he will forgive me and contact me again. The modern Basque settlers of Idaho may perhaps bring forth a linguist to investigate matters raised in this chapter. [p 173]
by Barry Fell
(1976)
find it in a nearby library