It's complicated. There's the paper linked in the other comment, there's hybrid vigor, and also people with rare phenotypes eg have trouble getting organ donati

It's complicated. There's the paper linked in the other comment, there's hybrid vigor, and also people with rare phenotypes eg have trouble getting organ donations. There's a diversity of phenotypes around the world because groups of humans have been in reproductive isolation. I'm sure that will continue for various reasons (assortive mating, religion or immigration restriction like many East Asian countries). From memory you need <2% inter-marriage rate per generation for your group to diverge. Some people want to preserve reproductively isolated groups, rather than form a larger gene pool (though this is betting against human lust and cheap air travel) If you are more related to your country than to the average human on earth (true historically), and your country adopt pro-natal policies rather than immigration of people who are genetically distant from you, you would increase the number of genes similar to you in the global population.