….Darwin thought that, had the circumstances for reproductive fitness been different, then the deliverances of conscience might have been radically different. “If . . . men were reared under precisely the same conditions as hive-bees, there can hardly be a doubt that our unmarried females would, like the worker-bees, think it a sacred duty to kill their brothers, and mothers would strive to kill their fertile daughters, and no one would think of interfering” (Darwin, Descent, 82). As it happens, we weren’t “reared” after the manner of hive bees, and so we have widespread and strong beliefs about the sanctity of human life and its implications for how we should treat our siblings and our offspring.
But this strongly suggests that we would have had whatever beliefs were ultimately fitness producing given the circumstances of survival. Given the background belief of naturalism, there appears to be no plausible Darwinian reason for thinking that the fitness-producing predispositions that set the parameters for moral reflection have anything whatsoever to do with the truth of the resulting moral beliefs. One might be able to make a case for thinking that having true beliefs about, say, the predatory behaviors of tigers would, when combined with the understandable desire not to be eaten, be fitness producing. But the account would be far from straightforward in the case of moral beliefs.” And so the Darwinian explanation undercuts whatever reason the naturalist might have had for thinking that any of our moral beliefs is true. The result is moral skepticism.
If our pretheoretical moral convictions are largely the product of natural selection, as Darwin’s theory implies, then the moral theories we find plausible are an indirect result of that same evolutionary process. How, after all, do we come to settle upon a proposed moral theory and its principles as being true? What methodology is available to us?
Paul Copan and William Lane Craig [Mark D. Linville’s chapter], eds., Contending With Christianity’s Critics: Answering the New Atheists & Other Objections (Nashville, TN: B&H Publishing, 2009), 70.
FYI, This book is a bit advanced… one of the best treatments of apologetics I have read in a while has been, Is God Just a Human Invention? And Seventeen Other Questions Raised by the New Atheists. Highly recommended.