Hi, Kristoffer Trolle
Ever since you first posted this topic, I have been digging on the internet for data on genetics of pre-communist countries, but I couldn't find any presentable evidence for the pretty obvious fact that genetic composition does change under communism. Genetics is a rather new field, and was certainly not applied before the rise of communism, and was even more certainly not applied during communism. Now... so far I have been only using the word "communism" for a reason. That is because it is a universally accepted theory that Communism is the ultimate form of Socialism. There have been some developments that, safe to speculate have had a considerable effect on the genetics of the population. Here are the big ones. Maybe you will have better luck finding data.
1. Purging of intellectuals: In almost all communist countries, the higher and intellectual classes (you know, the smart ones) were systematically eradicated. I don't think it is a question whether or not that affected the gene-pool. https://en.wikipedia.org/wiki/Great_Purge
2. Cultural Genocide: Socialists generally do not like culture, and are all very big on "progression" and leaving the past behind. This had manifested itself in the destruction of religion, manners, tradition, language and history. Example: The Great Leap Forward. https://en.wikipedia.org/wiki/Great_Leap_Forward
3. Population Control: For some sick reason, people like to control how many of the lowly peasants there are. The old communists were no exception. They promulgated decrees on how many children should be born, shamed women through media who had too many or too few children. We all know about the Chinese One-Child policy, but this has happened and is still happening in all socialistic governments. I posted a reference to a Romanian state action. I'm sure Wuzzums can tell more about it from a personal standpoint. https://en.wikipedia.org/wiki/Decree_770
4. Forced Labour Participation: It was literally a felony to not have a job in the old communist states. If I'm not mistaken, maternal leave was restricted to 3 months or even less in most countries. That has no doubt influenced the decisions of many mothers. https://www.jstor.org/stable/1937939?seq=1#page_scan_tab_contents
5. Orchestration of ethnic conflict: Although divide and counquer is an ingenious tactic short term, even Caesar failed at it eventually. Such was the case of Ceausescu of Romania, who tried to blame every problem in his country on the Hungarian minority and other hostile powers threatening the integrity of Romania. In his last speech ever, he does that as he always has, by then however, it has been sorely played out. That said, by this time, the percentage of the Hungarian population was halved compared to the pre-war era. https://en.wikipedia.org/wiki/Demographics_of_Romania
6. Transplantation of Populations: There were some crazy things socialists always fancied doing to ethnic groups, but probably one too much even for Sweden (don't get any ideas, Merkel!) is the literal uprooting of an entire country and its population, and transplanting it thousands of miles away, only to maybe return them to the same location a few years later.
An example of this is the expulsion and repatriation of the Chechen population. https://en.wikipedia.org/wiki/Aardakh
Another example, and most tragic in my opinion, is the displacement of the Germans of Prussia Sudetenland, Silesia, Transylvania, Hungary, Vojvodina, Volga and elsewhere. https://en.wikipedia.org/wiki/Flight_and_expulsion_of_Germans_(1944–50)
7. The big one... Feminism. I don't think I need to explain. Unfortunately, I could not find data aside from a book here that addresses the question of labour and women in the USSR It is not for free though, so I haven't read it: http://www.sciencedirect.com/science/article/pii/0147596783900835