If 'nature' is all there is, how can the 'basics' of matter in motion not apply? What else is there? Naturalistic assumptions will not permit anything other than the basics of particles of matter and energy. Darwinism insists on thoroughly naturalistic explanations based on material causes, doesn't it? Since naturalism assumes that everything in existence is the result of natural causes, that includes the chemical fizz you refer to as thoughts and feelings.
And ethical is what works best with man's interaction as a society.
Darwin purported to provide a naturalistic explanation for the emergence of morality. A claim of what is "best" assumes a moral standard by which society can be judged, which assumes the very thing in question. Morality cannot be explained simply by positing a prior moral rule since morality is what is supposed to be accounted for in the first place.
It is possible that such behavior is genetic, as more sympathetic societies passed on their genes because they were more successful. I am talking about how the eugenicists think only of physical traits, trying to "improve" the race by weeding out what they think is undesirable. What they don't realize is that their very actions are undesirable according to Darwin.
Both Darwin and Christianity agree on the subject, in opposition to the eugenicists. No surprise since Darwin was originally Christian.
Morality cannot be explained simply by positing a prior moral rule since morality is what is supposed to be accounted for in the first place.
Concepts of morality grew from what worked best for a society. They kind of noticed that murder did not make for a cohesive society, so it gets outlawed, in tribal rules and later in religion when that developed beyond "Ogg, Sun God angry" and into a mechanism for enforcing societal rules.