“I’m an atheist,” the late actress Katherine Hepburn once told an interviewer, “and that’s it. I believe there’s nothing we can know except that we should be kind to each other and do what we can for each other.”

Plainly, atheists can be, and often are, good people. It’s wonderful that Katherine Hepburn knew those things. I believe that she did know them; I hope that she acted accordingly. But how did she know them? It’s one thing to believe in moral principles; it’s quite another to be able to justify them, to give an account of their source. And this seems to me a particular problem for atheists.

“Morality,” writes the evolutionary atheist philosopher Michael Ruse, “or more strictly our belief in morality, is merely an adaptation put in place to further our reproductive ends. Hence the basis of ethics does not lie in God’s will — or in the metaphysical roots of evolution or any other part of the framework of the Universe. In an important sense, ethics as we understand it is an illusion fobbed off on us by our genes to get us to cooperate. It is without external grounding. Ethics is produced by evolution but is not justified by it.”

Once I’ve recognized that morality is an illusion, though, why should I feel bound by it — especially when I can safely ignore it?

“We are survival machines,” says the British biologist and vocal “New Atheist” Richard Dawkins, nothing more than “robot vehicles blindly programmed to preserve the selfish molecules known as genes.”

“What natural selection favors,” writes Dawkins, “is rules of thumb, which work in practice to promote the genes that built them. Rules of thumb, by their nature, sometimes misfire. In a bird’s brain, the rule 'Look after small squawking things in your nest, and drop food into their red gapes,' typically has the effect of preserving the genes that built the rule, because the squawking, gaping objects in an adult bird’s nest are normally its own offspring. The rule misfires if another baby bird somehow gets into the nest, a circumstance that is positively engineered by cuckoos. Could it be that our Good Samaritan urges are misfiring, analogous to the misfiring of a reed warbler’s parental instincts when it works itself to the bone for a young cuckoo? An even closer analogy is the human urge to adopt a child.”

But does adoption — or contributing to relief for unrelated poor people in distant countries, or risking one’s life to save a stranger — really represent mere evolutionary error?

To his credit, Dawkins himself recoils from the idea. He calls such acts “precious mistakes.” But why are they “precious”? What does that mean beyond the mere fact that he likes them, as he might like broccoli or the Beach Boys?

“The universe that we observe,” he’s also written, “has precisely the properties we should expect if there is, at bottom, no design, no purpose, no evil, no good, nothing but pitiless indifference.”

On what objective grounds, if any, can someone holding this view say that failure to help a child or fight Third World hunger is “wrong”? On what basis, even, can such a person condemn murder, rape or child abuse? If somebody else endorses them, on what basis can a Dawkins disagree? The Nazis regarded killing Jews and Gypsies and enslaving Slavs as good things. Are these only matters of opinion?

Another way of looking at them involves what members of The Church of Jesus Christ of Latter-day Saints call “the light of Christ,” something given to every human. It provides both basic moral intuitions and, ultimately, the grounds for holding all of us morally accountable. As the apostle Paul wrote, “Gentiles, which have not the law, do by nature the things contained in the law … which shew the work of the law written in their hearts” (Romans 2:14-15).

A simple argument can be formulated this way:

1. If there is no God, objective morality and moral obligations don’t exist.

2. But objective morality and moral obligations do exist.

3. Therefore, God exists.

The logic of the argument is valid, and I suspect that most people intuitively believe both of the premises. If they are granted, the conclusion follows.

Note: This column was inspired and influenced by essays by William Lane Craig and Chad Meister in William Lane Craig and Chad Meister, eds., “God is Great, God is Good” (Downers Grove, IL, 2009).

Daniel Peterson teaches Arabic studies, founded BYU's Middle Eastern Texts Initiative, directs MormonScholarsTestify.org, chairs www.mormoninterpreter.com, blogs daily at www.patheos.com/blogs/danpeterson and speaks only for himself.