Can morality be an evolutionary adaptation?

No. The idea is hopeless.

First, it destroys any basis for moral judgement. If morality is just a product of evolution (random mutation plus culling through natural selection), then it is perfectly possible that we could have evolved so that racism is a positive moral good (on the assumption that “moral” can only mean “in accord with an illusory belief produced by evolution”). Worse, there is no way to tell, on this theory, that we didn’t evolve so that racism itself is a positive moral good (again, on the theory’s claim that “moral” really only means “in accord with an illusory belief produced by evolution”). If I believe racism to be immoral and want to formulate a justification for my belief, to what possible standard of judgement can I appeal if we already know, because the theory tells us, that all such standards are equally the product of mindless and valueless evolutionary processes—of molecules bumping together in some ways but not in others?

That’s bad. But it gets worse.

If there is no objective moral reality in relation to which a moral injunction can be true or false AND if we affirm this to be the case, then, given this conjunction of conditions, it’s not clear that a moral injunction can form the basis of a moral belief at all. The evolutionary theory denies the existence of an objective moral reality, so when I am enjoined to do something (e.g., tell the truth) or to refrain from doing something (e.g., tell a lie), the claim on me as a moral agent can have no referent in moral reality. Moral injunctions refer to mere illusions produced by evolution, full stop. So to believe that the injunction imposes a real duty is to believe an illusion, according to the theory.

And what happens when we as moral agents accept this as a meta-ethical fact? Once we believe it to be the case that moral injunctions are ultimately illusory, we have a warrant to reject all beliefs based on moral injunctions. We have a universal defeater for all claims to moral duty. After all, it’s not rational to believe I am compelled to act or to refrain from acting based solely on an illusion, even a shared illusion. So morality itself is totally undermined on the conjunction of the theory being true and our belief that the theory is true.

That’s worse. But it gets worse still.

What of those who reject the evolutionary account—again, if we assume the evolutionary account is true for the sake of argument? What of those who persist in their moral realism? If the evolutionary theory is true, and all morality does in fact reduce to illusions implanted in us by the sorts of mindless and undirected forces described by the neo-Darwinian account of evolution, then there can be no argument with the realists. After all, why should realists prefer your illusion to theirs, particularly when arguing against realism requires the meta-ethical move of admitting that morality is an illusion, the exact move that completely undercuts the idea that we even have moral duties at all? The evolutionary theory fails versus realism precisely because it has closed itself off from any possible appeal to a universal moral reality and because believing it requires a meta-ethical move that totally undercuts even a consequentialist defense of morality: any injunction to believe in morality because it produces salutary effects despite the fact that is an illusion would itself be an illusion, and believing in illusions is irrational.

So to sum up: the evolutionary theory entails the belief that we could have evolved so that we have a duty to facilitate or thwart the intentions of others based solely on perceived race. And the adherents of this theory have no way to tell racists that we didn’t evolve so that racism is a positive good. And even if they simply asserted that racism is immoral, they would have no grounds for enjoining the racists to abandon their beliefs and reform—after all, the moral grounds for any reform would be just as illusory as the idea that racism is moral.