Progress
I see a challenge from that brief historical analysis in the previous section. Why, if ethics is based on social evolution, do societies sometimes devolve?
Evolution does not necessarily mean progress, just change. A society could degenerate as surely as it could progress.
In other words, the mechanisms for degeneration must be understood as well as those for progress.
Another thing forces a question for the fall of Rome. That the empire already lasted for a thousand years, clearly for most of which time being an indefinitely sustainable society. So what caused its ultimate degeneration? If the theory of ethics is based on social evolution, then how can it cope with the degeneration of societies? Do the societies' morals degenerate as much as the societies do themselves? If so, then one cannot really make any secure claim at any one time that our ethics must be superior to the ethics practised before, by our own values. Our ethics must be as good as the ethics practised...