Evolutionary biologist Jerry Coyne recently wrote about Leah Libresco’s conversion from atheism to Catholicism based on a moral argument for God’s existence. In his article, Coyne promotes the idea, which he has done many times before, that biological evolution somehow “explains” objective morality. While there is a sense in which Coyne is correct, that has nothing whatsoever to do with the kind of moral argument which Libresco finds persuasive. So while I join Coyne in rejecting Libresco’s argument, it’s unfortunate that such a prominent scientist as Coyne continues to perpetuate such an irrelevant response to such a popular theistic argument.

Two Popular Arguments for God’s Existence Based Upon “Objective” Morality

Allow me to explain. There are many types of moral arguments for God’s existence. Moral arguments based upon “objective” morality are arguments focused on moral ontology. Moral ontology is the branch of metaethics which is about the nature of moral claims; it asks whether any moral properties or facts exist and, if so, what metaphysical status they have (e.g., objective or subjective).

By itself, biological evolution is irrelevant to moral ontology. That doesn’t mean biological evolution is irrelevant to morality, of course. It’s clearly relevant to other branches of metaethics, such as moral epistemology and moral psychology. But it’s a category error to think that biological evolution explains moral ontology.

Consider the following two versions of the moral argument for God’s existence.

Version 1: William Lane Craig’s Deductive Moral Argument

William Lane Craig famously defends the following argument.

1. If God does not exist, objective moral values do not exist.

2. Objective moral values do exist.

3. Therefore, God exists

Notice what this argument does NOT claim. Contrary to many atheist debaters and bloggers, it does not claim any of the following.

• You cannot be moral without believing in God.
• You cannot know right from wrong without believing in God.
• You cannot have any motivation for behaving morally without believing in God.

Instead, the argument simply says that objective moral values exist, in the sense that moral statements like, “Rape is morally bad,” are true independently of whether any human believes it. If it’s objectively true that “Rape is morally bad,” then what makes that statement true? According to Craig’s argument, God–or, to be precise, being contrary to God’s nature–is what makes that statement true.

Version 2: C.S. Lewis’s Explanatory Moral Argument

I read somewhere that Libresco was persuaded by C.S. Lewis’s argument, so let’s turn to that version next. Lewis’s argument is much less clear for the simple reason that Lewis never stated his argument in its logical form. Nevertheless, we can reconstruct his argument. When we do, we find that Lewis argues that theism (what he calls the “Religious view”) is the best explanation for known facts in moral ontology, epistemology, and psychology.

Let’s begin by dividing Lewis’s evidence into B, the relevant background evidence, and E, the evidence to be explained. Then the evidence can be summarized as follows.

B: The Relevant Background Evidence

1. The materialist view entails that there is no Mind “behind” the universe (i.e., there is no Creator). The universe itself, as well as all the creatures inside it (including humans), are not the effect of a supernatural First Cause or intelligent Designer. (21-22)

2. The religious view entails that there is a Mind “behind” the universe (i.e., there is a Creator who is conscious, has purposes, and preferences). This Mind created and designed the universe partly to produce creatures that, like it, have minds. (22)

3. A Mind “behind” the universe could reveal its existence to us by trying to get us to behave in a certain way. (24)

E: The Evidence to be Explained

1. Human beings have moral obligations which are grounded in the Moral Law.

2. Most human beings know at least the general principles of the Moral Law.

3. Most human beings experience moral emotions related to the Moral Law, such as guilt and obligation.

With this evidence so defined, we may formulate Lewis’s as follows.

1. The evidence relevant to the Religious view is known to be true.

2. The materialist view has weak explanatory power.

3. The religious view has strong explanatory power.

4. Therefore, it is epistemically probable that the religious view is true.

Coyne on the Evolutionary Explanation for Objective Morality

Here is Coyne in his own words.

The reason she [Libresco] came back to Catholicism? “I’m really sure that morality is objective.” Libresco affirms that Christianity, in the Catholic form, offered her explanation that she found compelling. (I guess she doesn’t find evolutionary or secular explanations compelling. The rejection of those alternatives, especially given the evidence for them, baffles me. [italics mine]

The Irrelevance of Evolution to Arguments from Objective Morality to God

As my above remarks should make clear, I don’t think evolution is relevant to moral ontology. Regarding argument version 1, evolution is an irrelevant objection because it refutes neither premise of the argument. As for argument version 2, evolution at best helps the materialist explain moral epistemology and moral psychology. It does nothing to counter Lewis’s claim that the religious view provides a better explanation for moral ontology or objective morality (in his words, the “Moral Law”) than does the materialist view. Therefore, we should not be baffled by the fact Libresco (or anyone else) would find an evolutionary explanation for moral ontology compelling.