IIRC, in the Olalde 2019 study the authors claimed Iberia has almost no Germanic admixture after modelling Visigoths with use of very "northern" Pre-Roman samples as a source (while samples from times of the Roman rule in Iberia were no longer as northern-shifted as those Pre-Roman, due to admixtures from the east).
And that made no sense, because Celtiberian genetics got altered during Roman period. The authors used a biased model to prove lack of Germanic DNA.
Here the authors have the opposite agenda - and are also using biased models. In this case it would actually make sense to use Republican samples, because - unlike Celtiberians in Iberia - Republican Romans could survive Imperial era unaltered. Imperial samples so far are only from Rome and vicinity, not from all over Italy.
We should wait for a comprehensive study with samples from all over Italy including various rural areas, just like Olalde 2019 sampled most of Iberia.
I don't think they're necessarily biased. That will and is coming from the amateur community.
I just don't think they thought things through, and they have a high schoolers understanding of Roman history and that of Late Antiquity and the Early Middle Ages, if that. Some of their commentary sounded like a study note card from Middle School.
They also don't seem as conversant with the findings of other papers as we are, which is indeed worrying.
Still, at least, unlike Hellenthal and his group, they get that the "Southern" group was already there and didn't arrive with the Byzantines. I wonder if that group remembers the texts I sent!
Indeed, I wonder if the group over at Anthrogenica and Polako remember all the arguments they put forward for a huge movement from the east during Late Antiquity. I mean, it couldn't be more ironic. The change was the other way.
I have no problem with the change in Central Italy coming about because of input from Goths and Lombards. Well, I have a personal problem with it, as I don't like the idea of these destroyers entering our bloodlines, but I try to keep personal feelings out of it. I've accepted the Indo-Europeans, after all.
I had little choice. My father carried U-152, and unlike certain dead enders, I don't think it derives from WHG. Then there's my U2e, so there's that as well. They came, and that's an end to it.
I just don't see the evidence for this, however.
The Lombards' own chronicler, Paul the Deacon, said there were only 60,000 of them, including women and children. All the samples we have so far are U-106. Now, in the Veneto, and to a lesser extent in the rest of Northern Italy, we do see settlement patterns, some of which have survived, indeed, the very holdings have survived, and we do see U-106. We also see I1. Whether that came from other types of Lombards or from Goths or Franks from later on I don't know. Now, there isn't a lot of it, but it's there.
It's true that the Lombards established kingdoms elsewhere in Italy, including further south. However, those were some knights and their retinues. It was in no way a mass migration. You can get spikes of yDna because of founder effects, but for substantial autosomal change, which this was, you need a lot of it. I'll repeat my example of my area of Italy. The people plot firmly as north/central Italians, and yet they're over 70% R1b.
Where is all that U-106 and I1 in modern Lazio?
Now let's turn to IBD analysis. It's unlike IBS and more reliable in my opinion. So, unlike you, I don't think Olalde was wrong about there being very few signs of Germanic dna intrusion in Spain. Ralph and Coop found the exact same thing, i.e. very little sign of genetic change coming from the Germanic tribes in either Spain or Italy. I do think it makes sense. These were elite invasions, not mass invasions.
So, how did the change come about? Could there be other factors? I do think looking at Italians further north is a possibility which should have been explored. The change doesn't seem to be stemming from central/east Europe, but rather from northwestern Europe. Isn't that precisely what was more present in northern, especially northwestern Italy.
I'm not at all saying, by the way, as I tried to explain upthread, that Central Italy didn't remain more "southern" than it was at the time of the Republic. There's a great deal of Greek like ancestry in Italy. However, I just don't see evidence yet that the change was because of Goths and Lombards.
The disappearance of that "tail" into the Levant is a different matter. The mass decline in J1 should tell part of the story. The authors should have looked at the differences in ancestry per each burial site, as I tried to do in a quick and dirty way. There seems to be a difference, which would support their own statement about the heterogeneity of these Roman populations. It wasn't a melting pot; it was more like a stew.
There were probably ethnic "enclaves", as there are in any great city where there's been a lot of migration from foreign parts. Look at London, or New York. In a couple of hundred years those differences aren't going to disappear. As trade dried up, people moved to more advantageous locations, and then there was the sacks and mass destruction. Those who had the ability or contacts elsewhere fled. The others would have died.
These are patterns which are repeated over and over again in history. You just have to read it, a lot of it, and try to learn from it, from it and archaeology, and not just play with algorithms. I tried telling the usual suspects not to include Messina in their attempts to figure out ancient migrations specifically to particular areas of Sicily. There was a massive earthquake at the beginning of the 20th century. Very few people survived. Where did most of the resettlement come from? Calabria across the water.