Now you're arguing the validity of his views, which isn't the subject.
How do you derive actual moral obligation from a mere description of animal behavior conditioned by the environment for survival?
These were observations of what makes a human society powerful vs. simple genetics. Darwin was showing how his theory of physical natural selection at animal level does not apply to human society, yet those in favor of eugenics ignored him, and still his enemies blame him for the views of the eugenicists.
Darwinism does not make any argument against eugenics at all because if it is taken to its logical conclusion it eviscerates any foundation for morality.
You are again changing the subject to the origin of morality. In this sense what makes for a sympathetic society, a society that will be stronger and longer-lasting than those around it, is the foundation of morality. These rules were later written into various religions as absolute morality.
I don't suppose you've noticed that Christians, who have one of the best sets of moral laws in the world, dominate this world. Muslims are a freak, as they dwindled into irrelevancy, their societies dying out, until it turned out the horrid places they settled (the places the stronger societies didn't want anyway for the most part) were rich in valuable natural resources. That accident of geography upset the natural order according to Darwin, which is that unsympathetic societies will die out.
Couple that with many Christian societies becoming quite unsympathetic, as you see with the prevalence of abortion, not taking care of our elderly, etc., and you see how Christian power has declined.
How am I changing the subject when it is Darwin himself who attempts to give a biological explanation for man's moral faculties in chapters four and five of The Descent of Man?
In this sense what makes for a sympathetic society, a society that will be stronger and longer-lasting than those around it, is the foundation of morality.
As per Hume, It is invalid to derive "ought" from "is." No ethical principle can be legitimately founded on a fact of nature, so biological principles cannot be translated into moral imperatives. My point is that Darwin's insistence on the continuity of man and animals vitiates any foundation or justification for his own transcendent ethical pronouncements, e.g., "happiness is an essential part of the general good." in chapter 21 of the book. His premises are self-defeating.
As Thomas Huxley put it,
The thief and the murderer follow nature just as much as the philanthropist. Cosmic evolution may teach us how the good and the evil tendencies of man may have come about; but, in itself, it is incompetent to furnish any better reason why what we call good is preferable to what we call evil than we had before.A foundation devoid of ethical content is no foundation at all.