I see that same people who suggest that steppe-less Hittite samples are not representative and belong to Hattians now suggest that these Roman samples belong to mercenaries, slaves etc.
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We can't possibly know that yet, right?
I mean, she didn't give any clues as to whether certain types were from tradesmen or middle class, "local" people with "local" or "Italian" isotope values, and other types were from Ostia and other ports, where you might expect traders, or from slaves' graves.
Plus, it depends on the period, I think. Republican Era Rome was 60% modern Northern Italian like and 40% Southern Italian like, so I think the mercenary, slave thing is a non-starter for that period. It may be a reflection of the admixture between originally Italic speaking newcomers and the natives. We can't know because we have only one set of samples from southern Italy, and that's from just one corner of Sicily which had some Beaker influence. As Markod said, we need samples from Samnites and further south too, and from Etruria.
I don't know what anyone could mean about "mercenaries" in Rome itself. It must be from someone who knows nothing about Roman history. If by "mercenaries" they mean Roman auxiliaries, then I think it's still a non-starter for a big chunk of the time. Until into the Empire, the legions were primarily composed of people from the Italian peninsula.
The later Imperial period is different, but even then, most of the legions were stationed abroad, not in Italy, and certainly not in Rome.
As for slaves, they were present in the Republic and later and in increasing numbers in the Imperial period, as were foreign merchants, and even groups like the Jews. It's hard to know how many would have contributed to the succeeding generations. So much depends on the genetics of groups further south in the Italian peninsula, who would definitely have been incorporated into the population.
Generally speaking, I don't think most slaves had surviving progeny, certainly not miners, or galley slaves, or slaves worked to death in latifundia. Freed slaves of the type who would be working in Rome would only have progeny if they were freed (The Romans didn't have "breeding" farms as happened in the American south: more conquests meant there were always more slaves.), but you would normally be freed in later life, so less of a chance for surviving descendants.
It always amuses me that in the imagination of these people all of the Roman slaves were from West Asia or North Africa.
Don't they know how many slaves were taken from Gaul, conveniently nearby, and the Balkans, and Germania, and Spain. Selective vision, I guess.
That's what happens when you approach everything through the lens of your own particular agenda instead of just following the facts.
There's also the fact that urban centers are always the ones most destroyed during wars and invasions. I doubt most of the Imperial residents of Rome survived.
Does this have anything to do with the Collegno samples? I don't think that we can extrapolate from them to all of Northern Italy at that time, although it is certainly true that Rome settled veterans there, and many would have been from southern Italy. As you can see below, the majority of the colonies were in the center. If a good part of the veterans were from southern Italy and Sicily, then that might partly explain the changing demographics. There are few in the Po plain because a lot of it was swamp until the Romans drained it.
That should be added to the video, i.e draining swamps, thus producing more farmland and tamping down malaria.