I think that he was talking about cultural evolution, not biological evolution. Tribalism is a product of cultural evolution...
Culture (the thing that binds tribes) and tribalism are products of biological evolution, as they did provide individuals with reproductive/survival advantages in millennia past.
Mental illness during that period of time would have been whatever impulses failed to confirm or conform to the idea that "my tribe is the best tribe". Now that tribalism has become a threat to the continued existence of the species and doesn't confer any reproductive advantages to individuals, tribalism
can be thought of as a mental illness.
IOW, the utility of the label - "mentally ill" in this context is less than zero. In fact, as applied to an individual because of a retained tribalist trait, it holds the same meaning as "stable genius".
On a practical level though, if the white supremacists want to insist on their own sanity, then I guess it's okay to lock 'em up or put them to death if they shoot a bunch of people, right?
No, only when they break laws. And I don't support the death penalty in any case. It implies a certain perfection in our justice system that it has never deserved.
It is common to believe that everything about an organism is the way that it is because of evolution and natural selection, but it is far from the truth of the matter. Random genetic drift probably has more to do with you the way that you are than evolution and natural selection. Your DNA is mostly junk to which most mutations don't matter. Mutated junk is still junk.
As Toni pointed out, biological evolution happens over millions of years, where cultural evolution happens over decades and centuries. Some people are tribal and some aren't, but it is not because of our genome like fight or flight is.
People want to justify racism, for example, based on the human genome, that there is a fundamental difference between the so-called races beyond the obvious; skin tone, nostril flare, hooded eyes, etc. That these rather superficial differences affect intelligence, initiative, etc. Biological evolution is going on all of the time, but it is an extremely slow process and on a human time scale we can't detect it. What happens rather rapidly are certain characteristics becoming sexual preferences like hooded eyes in the orient. These are localized cultural changes, empathizing certain physical characteristics, not changes to the human genome. In other words, these types of changes aren't biological evolution, they just increase the percentage of humans with hooded eyes.
Likewise, the fact that European Jews have a higher intellect than average or that the Chinese study more in school or that humans who migrated to the northern latitudes lost the melanin in their skin or that some people have blue eyes that never turned brown are all cultural evolution or sexual preference selection, not biological evolution. All of the changes above and many more are short term cultural evolution caused by local conditions.
The European Jews couldn't own land in Europe, they had to learn to live by their intellect as teachers, lawyers, doctors, bankers, and merchants. The landowning gentry didn't need to live based on their intellect, their future was usually sealed at birth. They would either inherit the land or their older brother would.
The genius of the Confucian system of government was that a position in the apparatus of the government was rewarded based on merit alone, not on the social order as in Europe. This put a premium on education across the whole Chinese society that continues to today, even if Chinese mothers don't know why they nag their children to study hard to do well in school.
The people in the northern latitudes lost the melanin in their skin because they needed to take in more vitamin D from the reduced sunlight in the north.
Every person who has blue eyes is a descendant of a single individual who lived 6,000 to 10,000 years ago. If the parents of the individual thought that blue eyes were a mark of the devil and killed the baby, we probably wouldn't have any blue-eyed people today. But they didn't.