[Junior]

What is the source of the moral rule that I ought to be unselfish? Saying that because it is better for me and mine somehow just doesn't sound like a justification of the moral rule that I should be unselfish.

Not a justification, but a source, as it were. This trait has been selected for for millennia.

[Diamond]

Not a justification, but a source, as it were

I'm sorry - I meant justification as the source of the moral rule.

It seems to me that to say descriptively that the trait has been selected for millennia does not explain where the requirement came from or why it is incumbent upon me to obey it as a moral rule in the future. You have to presuppose a prior morality before there is any right or wrong, but then how can natural selection account for what came before it?

Cordially,