That is his point—that the civilized are weakening their breed.
Yes. They’re weakening the body by allowing the cancerous weaker races to grow.
The Germans believed they killed first the disabled and later homosexuals and Jews to purify their body politic. They felt it was part of the evolutionary process and an act of self defense. All of that flowed directly from Darwinian theory of a post-Christian post-God society which would emphasize strength and power.
It’s amazing Americans know nothing about Eugenics when we were the world leader. A Supreme Court Justice in approving of forced sterilization wrote that three generations of morons were enough. Germans even came here to study Eugenics and various programs states had implemented.
Of course, the most famous social Darwinist was Margaret Sanger. Killing off the poor and minority babies was part of the advancement of society to her.