First, even without changes in human nature, morality is pretty darn flexible. Just a couple of centuries ago slavery was widely accepted as moral. Today it's a moral abomination.
Nehru jackets were once fashionable, too. If morality is just convention then if acting morally conflicts with self-interest why should we act morally? How is a nonconformist who chooses to flout the herd morality doing anything other than acting un-stylishly? What rational justification can be made in such a case that flouting current convention is doing something "good" or "evil"?
Cordially,
Good is what makes people better off and evil is what makes them worse off.
When we feel we ought to do some things and not other things, is that obligation real? ...
The feeling that you're obliged to do A but not B is real. I think we can agree on that. It's part of that innate, objective human nature I talked about. We want to get along with others, it's normal.
But I think the answers to the rest of your questions are unknowable. Tell me what test I can do to decide if I have some real moral duty to the universe? Maybe someday it will be possible for us to answer the question. Maybe we'll discover the universe has a real moral rule. But maybe not. I can't say.
If morality is just convention...
It's not just convention as I thought I'd made clear in my first post to you on the thread.
But that isn't the whole story. I think there is a real, objective human nature, behavioral traits shared by all, some few abnormal people excepted. Hierarchical social structures is an example. Morality builds upon, or tends to respect, these shared values.