European IQ Differences: Deep Roots, Dysgenics, or Brain Drain?
All 3, probably.
IQ by country in Europe:
There are several factors that can lead to national differences in IQ. Among them:
Admixture: the higher a country is in PC1, the higher the national IQ is. Some disparities still remain: Ukrainians are about 5 points below Russians, but are genetically almost identical to them. The same goes for Hungarians and Romanians, where Hungarians surpass Romanians by 10 points.
Dysgenics: high regional outliers (Netherlands, Estonia, Finland) have extremely weak dysgenics. The same goes for the low ones (Romania, Macedonia, and Albania).
Muslim effect: Bosnia, Albania, Montenegro, Macedonia, and Kosovo are clearly underperforming relative to their regional neighbours
Brain Drain: theoretically this should be a massive issue, but it’s hard to quantify.
Environmental factors: some countries (e.g. Turkey, Serbia) have recently risen in cognitive ability quite a bit. It wouldn’t be out of the question that some of these differences could reduce in magnitude within the next 20 years.
II.
Brain drain is the 3rd potential cause -- theoretically this should be an issue, but it’s difficult to quantify because not all emigrants are the same; some of them are low class janitors/plumbers, while others are doctors or academics.
While immigration/emigration rates do seem to correlate to national IQ, the effect does not seem to be consistent -- Romania and Poland have similar levels of emigration but a large difference in national IQ (98 in Poland and 87 in Romania). This still seems to be in play in the younger generation, with Poland scoring at ~515 in the latest PISA results and Romania scoring a ~420, a difference of about 1 standard deviation.
Out of all causes, admixture seems to be the largest cause of differences in IQ between European nations, likely due to interbreeding with Arabs and Turks, which happened when the South East was ruled by the Ottomans and Iberia was ruled by the Berbers. Immigration and interbreeding between European nations is not heard of, so the effects of these invasions should lower the average IQ of the neighbouring regions.
Outliers that are difficult to explain with admixture:
Netherlands (100): low dysgenics.
Finland/Estonia (101-102): low dysgenics.
Moldova (87.9): brain drain.
Ukraine (92.5): brain drain.
Romania (87): high dysgenics and brain drain.
Albania/Macedonia/Kosovo (78-85): Muslim effect.
I've heard that Albanian/Bosniak IQ is low because of brain drain, just a long while ago and for a long period of time. This is also why Irish/Scottish IQ is a bit lower than English IQ (used to be? Or was this always just a product of bad studies?). Albanians basically became the administrative elites of the Ottoman Empire and a huge amount of the intelligent and capable ones were sent to Anatolia or the Middle East. I'm pretty sure Albanians are still high-status in former Ottoman areas today. Muslim effect (let's be honest -- polygamy) can definitely not explain the severity of this
'Nordic' (largely northwest) mental age is 13.8% higher than that of the 'Alpine' (central to east) mental age—the 'Nordic' mental age is 16.2% higher than that of the Mediterranean. In general Northern Europe is as much as 21% higher than Southern Europe, and Western Europe as much as 23% higher than Eeastern Europe, regarding mental age. This is according to results in Carl Brigham's study of American Intelligence, 1923.
According to your estimations of IQ, Northern Europe appears to be at least 6% higher than Southern Europe.
In 'Comparison of cognitive and physical functioning of Europeans in 2004-05 and 2013', Northern European cognitive function is 19.6% higher than that of Southern Europe. The same study finds Northern European grip strength to be 13.8% higher than Southern European grip strength; https://akarlin.com/strength/ A. Karlin collected data illustrating a great gap in strength between North and South.
Lactose intolerance is 37-56% higher in Southern Europe than Northern Europe. Eastern Europe is 32-51% more lactose intolerant than Western Europe, studies like from the Lancet compilation show this. In most cases it can be found that chronic conditions are more common in Eastern Euros than Western Euros as well.
Overall the divide has been consistent for quite a while and is evidently largely constitutional, while brain drain and dysgenics reinforce the differences.