> Thanks for the review. The biological adaption relates to descriptive morality, whereas I focus on normative morality.

That's far too quick and dismissive. I too am talking about the normative notion, there's just nothing more to that notion than the biological fact of it, nothing beyond that contingency that gives it anymore normative oomph (but nor should we care). But such an account is of course still normative because it describes morality as being action guiding. This is the standard sort of move that Darwinian philosophers like Mackie, Rorty, Ruse, Street, or Joyce will make. It's about naturalizing morality, not about presenting a "merely descriptive" account as opposed to a normative one. Even idealist philosophers like Rawls and Kant are simply giving a "descriptive account" of our intuitions about morality and justice in the same way I am, but this doesn't make their account any less normative than my own or that of other evolutionary ethicists.

> If the problem is with discovering non-reasonably rejectable reasons, then it's only a problem of administrability.

It's not, it's about defining what it means to be "reasonable". Like, sure, there is the further problem of actually figuring out what reasonable people would agree to, but that's largely derivative of your definition of what constitutes a reasonable person.

> However, what else would morality be, the code of conduct of our treatment of others, if it could not be reasonably accepted by others?

It could be a fact of the matter. It could be a collective delusion. It could be an optimal solution to a particular set of game theory problems. There are many things it could be beyond the Kantian notion you're endorsing.