Genetics of Europe
This post is provoked by a steady stream of genetic nonsense coming from a couple of prolific commentators. As it happens, this is an area I have recently studied and I have a modest familiarity with the literature. Modern Europeans derive most of their ancestry from at least three waves of settlement, ultimately from Africa, via the Middle East. The first wave or waves consisted of hunter gatherers who interbred with Neandertals. They were pushed back into a few refugia (Spain, Italy, Greece) during the peak of the last ice age, but spread out again after the ice retreated 11,000 years or so ago. About eight millennia ago, a second wave, neolithic farmers from the Middle East, spread through Europe, and mixed with remnants of the hunter-gatherer populations. The Basques of Spain seem to retain relatively unmixed genetics from these farmers. A three or four millennia later, Central Asian pastoralists speaking Indo-European invaded and mixed to various extents with the preceding populations. Their languages, including Celtic, dominate nearly all of Europe today.
Celtic is a language grouping which at one time dominated much of Europe. Descendants of Celtic speakers are genetically diverse. Many of the languages of pre-Carthaginian Spain appear to have been Celtic. See Wikipedia:https://en.wikipedia.org/wiki/Pre-Roman_peoples_of_the_Iberian_Peninsula
Genetics of the Iberian Peninsula
Spanish genetics are complex, due to repeated waves of immigration and colonization. Aside from the Basques, who are largely unmixed with the later waves of immigration, the Spanish incorporate genes mostly from the pastoralists together with those of Greek, Phoenician, Carthaginian, Roman, Visigoth and Arab conquerors. Consequently, modern Spanish populations includes a lot of genes from all these areas including North Africa and sub-Saharan Africa.