

Why does humanity have less genetic diversity than any other mammal that’s not critically endangered?
Probably because of some event in the past that few individuals survived, so that all humans since have been descended from them. Homo Sapiens is a relatively recent species so the genetic narrowing effects of such population reduction would still be felt today.
But it has nothing to do with character or temperament, and as far as I know there’s no evidence Homo Sapiens actively killed off its close relatives. For whatever reason they died off, while at some point we almost did too, but we just scraped through with less diverse genes as a result. That’s how it goes in evolution: tiny differences can sometimes be amplified due to environment and chance. It’s absurd to draw political conclusions, and to do so shows a misunderstanding of evolutionary processes and history.
An article about this:
https://www.science.org/content/article/how-we-lost-our-diversity
And a fun (but long!) video about the misuse of evolutionary theory to support psychological, political and social conclusions:
He has two children with his own stepdaughter.