Freeman Dyson explains why cities, and indirectly, interracial relationships, are inherently dysgenic:
If a small population is inbreeding, the rate of drift of the average measure of any human capability scales with the inverse square root of the population. Big fluctuations of the average happen in isolated villages far more often than in cities. On the average, people in villages are not more capable than people in cities. But if ten million people are divided into a thousand genetically isolated villages, there is a good chance that one lucky village will have a population with outstandingly high average capability, and there is a good chance that an inbreeding population with high average capability produces an occasional bunch of geniuses in a short time. The effect of genetic isolation is even stronger if the population of the village is divided by barriers of rank or caste or religion. Social snobbery can be as effective as geography in keeping people from spreading their genes widely.
A substantial fraction of the population of Europe and the Middle East in the time between 1000 BC and 1800 AD lived in genetically isolated villages, so that genetic drift may have been the most important factor making intellectual revolutions possible. Places where intellectual revolutions happened include, among many others, Jerusalem around 800 BC (the invention of monotheistic religion), Athens around 500 BC (the invention of drama and philosophy and the beginnings of science), Venice around 1300 AD (the invention of modern commerce), Florence around 1600 (the invention of modern science), and Manchester around 1750 (the invention of modern industry).
These places were all villages, with populations of a few tens of thousands, divided into tribes and social classes with even smaller populations. In each case, a small starburst of geniuses emerged from a small inbred population within a few centuries, and changed our ways of thinking irreversibly. These eruptions have many historical causes. Cultural and political accidents may provide unusual opportunities for young geniuses to exploit. But the appearance of a starburst must be to some extent a consequence of genetic drift. The examples that I mentioned all belong to Western cultures. No doubt similar starbursts of genius occurred in other cultures, but I am ignorant of the details of their history.
West’s neglect of villages as agents of change raises an important question. How likely is it that significant numbers of humans will choose to remain in genetically isolated communities in centuries to come?
You know the current situation is becoming entirely unsustainable when both the traditional religious perspective and the secular scientific perspective are increasingly in alignment concerning the pressing need to eliminate big cities.
Ironically, despite the 20th century being known for eugenicism, it may prove to be the biggest experiment in dysgenics that Man will ever know. The Alt-Right is not only scientodific, it is apparently necessary for future human achievement, if not survival.