And this is why an evolutionist’s attempts to lay claim to a moral framework – as Dawkins and Hitchens are fond of doing – fail. Atheistic morality does not distinguish “is” from “ought” and without cosmic justice, there is no “ought” and no morality.

This article by Dinesh D’Souza is most illuminating on the subject; the whole thing is well worth a read here:

Cosmic Justice
If evolution cannot explain how humans became moral primates, what can?

By Dinesh D’Souza
All evolutionary attempts to explain morality ultimately miss the point. They seek to explain morality, but even at their best what they explain is not morality at all. Imagine a shopkeeper who routinely increases his profits by cheating his customers. So smoothly does he do this that he is never exposed and his reputation remains unimpeached. Even though the man is successful in the game of survival, if he has a conscience it will be nagging at him from the inside. It may not be strong enough to make him change his ways, but it will at least make him feel bad and perhaps ultimately despise himself. Now where have our evolutionary explanations accounted for morality in this sense?

In fact, they haven’t accounted for it at all. These explanations all seek to reduce morality to self-interest, but if you think about it, genuine morality cannot be brought down to this level. Morality is not the voice that says, “Be truthful when it benefits you,” or “Be kind to those who are in a position to help you later.” Rather, it operates without regard to such calculations. Far from being an extension of self-interest, the voice of the impartial spectator is typically a restriction of self-interest. Think about it: If morality were simply an extension of selfishness, we wouldn’t need it. We don’t need moral prescriptions to tell people to act for their own benefit; they do that anyway. The whole point of moral prescriptions and injunctions is to get people to subordinate and curb their selfish interests.

[……]

Now let’s make the supposition that there is cosmic justice after death and ask, Does this help to explain the great mystery of human morality? It seems clear that it does. Humans recognize that there is no ultimate goodness and justice in this world, but they continue to uphold those ideals. In their interior conscience, humans judge themselves not by the standard of the shrewd self-aggrandizer but by that of the impartial spectator. We admire the good man, even when he comes to a bad end, and revile the successful scoundrel who got away with it. Evolutionary theories predict the reverse: If morality were merely a product of crafty and successful calculation, we should cherish and aspire to be crafty calculators. But we don’t. Rather, we act as if there is a moral law to which we are accountable.