Razib passes on a 2019 article about income mobility in the US, relating it back to the patterns of income mobility in the countries in the European countries they come from. Data on blacks in the various regions are included for comparison to illustrate more general mobility.
Income inequality in both the US and Europe is quietly regarded as a bad thing, while countries more equalised because of their social welfare systems, it is directly claimed, are put forward as good things. The study shows that there is some connection which they call historical, that people who show income mobility here tend to come from places with higher income mobility in Europe. The authors are quite clear that this has to do with what is taught to children by parents from these differing European cultures.
They do not claim that the ethnicity explains all the variation. The region of the US matters some as well. As a small point to notice for those who follow this sort of thing, what is called British ancestry is known to many of us to fall into four broad categories, all of which have been in the US 200-400 years, and we know where they went. So the denser areas are Northern New England and Appalachia (and Utah, showing strong LDS influence), both of which have higher percentages of Scots-Irish than, say Southern New England, NJ, Pennsylvania. That might matter, though I wouldn't assert that without a lot more supporting data.
Missing from this analysis are the usual suspects.
Could there be anything genetic, even at a minor level, which explains greater or lesser mobility? Might some of the European nations have more height, or cooperativeness, or higher IQ, or some personality characteristics? If so, they might do better or worse accordingly.
Are these less equal and more equal countries different in any way in terms of how many outsiders they have been letting in to live there over the last hundred years? Might that not contribute to inequality in some way? Or are the presence of social welfare, plus the things you say to your children, the only drivers of that?
If, as the authors clearly want you to believe, it matters for social mobility in the US what the ancestry of the immigrants is, might it not also matter who moved in to those countries back in Europe, over and above the raw numbers? The immigrants of the highly unequal countries of UK and Italy - would they be about the same as the immigrants into Denmark? Just as an example.
Nah. We all know those things can't possibly matter and aren't worth studying.