Evolutionary Biology might be good at telling us what we value. However, as GE Moore pointed out, ethics is about what we SHOULD value. What evolutionary ethics will teach us is that our mind/brains are maleable. Our values are not fixed.
And the question of what we SHOULD value makes sense because our brains are malleable. Our desires - just like our beliefs - are not fixed. They are learned. So, the question arises, "Given that we can mold desires into different forms, what SHOULD we mold them into?"
Besides, evolutionary ethics is incoherent. "I have evolved a disposition to harm people like you; therefore, you deserve to be harmed." How does a person deserve punishment just because somebody else evolved a disposition to punish him.
Do we solve the question of gay marriage by determining whether the accusers actually have a genetic disposition to kill homosexuals? And if we discover they do, we leap to the conclusion that homosexuals DESERVE to be killed?
Why evolve a disposition to punish? That makes no sense.
What is this practice of praise and condemnation that is central to morality? Of deserved praise and condemnation? Does it make sense to punish somebody for having the wrong genes?
What, according to evolutionary ethics, is the role of moral argument?
Does genetics actually explain such things as the end of slavery, and a woman's right to vote? Those are very fast genetic changes.
The reason that the Euthyphro argument works against evolutionary ethics because - regardless of what evolution can teach us about what we do value, it teaches us that our values are not fixed. Because values are not genetically determined, there is a realm in which it is sensible to ask about what we should value, which is a question that evolutionary ethics cannot answer. Praise and condemnation are central to our moral life precisely because these are the tools for shaping learned desires - resulting in an institution where the question of the difference between right and wrong is the question of the difference between what we should and should not praise or condemn.
Its lunchtime so for fun I will answer some of your rhetorical questions.
Evolutionary Biology might be good at telling us what we value. However, as GE Moore pointed out, ethics is about what we SHOULD value.
Unless GE Moore is either an alien or an artificial intelligence, he is telling us what we should value from a human brain that values things based on its evolution. How will he be able to make any value statement and tell you with a straight face that his valuing that thing has NOTHING to do with his evolution?
...Besides, evolutionary ethics is
Do you believe in an objective morality capable of being scientifically investigated (a la Sam Harris *or others*), or are you a moral nihilist/relativist? There seems to be some division on this point. I would have thought Less Wrong to be well in the former camp.
Edit: There seems to be some confusion - when I say "an objective morality capable of being scientifically investigated (a la Sam Harris *or others*)" - I do NOT mean something like a "one true, universal, metaphysical morality for all mind-designs" like the Socratic/Platonic Form of Good or any such nonsense. I just mean something in reality that's mind-independent - in the sense that it is hard-wired, e.g. by evolution, and thus independent/prior to any later knowledge or cognitive content - and thus can be investigated scientifically. It is a definite "is" from which we can make true "ought" statements relative to that "is". See drethelin's comment and my analysis of Clippy.