I'll lift one statement out of their paper and offer some further comments on it.
In speaking of the origins of our "moral sense" they write,
Perhaps a divine creator handed us these universal elements at the moment of creation. But an alternative explanation, consistent with the facts of biology and geology, is that over millions of years we have evolved a moral faculty that generates intuitions about right and wrong.Interaction
I'd like to make four brief points related to an evolutionary justification for moral realism:
1. Its speculatory
This statement gets a lot of its traction by hitching its wagon to a name. Whatever the merits of the biological theory of evolution, the above claim is not a biological theory. It's not a scientific at all. It's speculation.
2. Disputed even by evolutionists
Another evolutionist doesn't think this works as a justification for why x is right or wrong. So Mackie, "If there were objective values, then they would be entities or qualities or relations of a very strange sort, utterly different from anything else in the universe. Correspondingly, if we are aware of them, it would have to be by some special faculty or moral perception or intuition, utterly different from our ordinary ways of knowing anything else" (J.L. Mackie, Ethics: Inventing Right and Wrong, 1977, p.38).
3. It fails to answer the deeper questions
When looking for an answer to metaethical questions, like what makes a moral fact a fact, this theory is wide of the mark. This theory, at its best, only provides a story for why we have certain moral feelings that we do. It doesn't explain moral facts. To explain a little further, take a non-moral fact:
(NF) Some Ball pythons eat mice.
Now, what makes (NF) true? Presumably, it is that what (NF) states is the case, is the case. (NF) is true because it corresponds to the way things are. It corresponds to some non-linguistic feature of the world. So (NF) is true if there is, in fact, some particular Ball python that eats some particular mouse. It matches up to a feature of the world. Without getting into theories of truth too much, the above account seems close to stating the matter correctly. We all can see, pretty easily, how a statement like (NF) would be true.
Now, let's look at a moral fact:
(MF) It is wrong to molest a child for fun.
On a naturalistic story, what would it mean for (MF) to be true? Presumably something like for what it was for (NF) to be true. But it is hard, to say the least, to see how this account would fit in with the naturalist story. I'll offer three reasons:
i) (MF) has moral properties, such as rightness or wrongness. What does it mean to say that rightness or wrongness is "part of the way the world is?" Unlike (NF), we cannot just "see" the wrongness of the act. And it would seem that the moral properties are necessary to explain the fact if one wants to hold to some kind of objectivism or realism.
But a non-realist naturalist could offer an account that did not refer to moral terms at all, just natural ones. For example:
Chester the molester was an extremely loving person. Because of various false beliefs about young children (most importantly, that they loved him), he found that 'molesting' children to be a satisfying way to release his love. His moral beliefs did not place any bounds or restraints on his expression of that love.
I borrowed this illustration, though changed the specifics, from Thomas Carson (Value and the Good Life, Notre Dame Press, p.194). Carson goes on to say that, "moral properties seem to be dispensible for explanatory purposes. Natural properties seem to be doing all the work in the explanations in question" (ibid, 198)).
So given the constant berating on behalf of the scientific naturalist about the principle of parsimony, it's hard to see why the don't just use "the razor" to "shave off" appeals to moral properties. For example, they feel that they can explain all mental properties naturalistically, so there is no need to appeal to some immaterial mind.
ii) If there were no Ball pythons or mice, then (NF) wouldn't be true. However, even of there were no molesters, or children, it would still be the case that it is wrong to molest a child for the fun of it. So (MF) seems to be different from (NF) in this regard too.
iii) (NF) is true because of the way some part of the world is. Conversely, (MF) is made true by the way things ought to be. (MF) is normative. It is not descriptive like (NF).
It carries with it an obligation (though, in a sense, from a Christian perspective, so does (NF), since it is true, we are obligated to believe it, cf. John Frame, DCL).
So, based on these reasons, (MF) facts seem to be very different, even "odd," as Mackie taught us to say, from (NF) facts. It is hard to see how (MF) facts are made true in a naturalistic worldview. And it is certainly the case that Singer and Hauser's evolutionary story do not offer us any help in this regard.
(Cf. Ganssle, Thinking about God, pp. 87-89, for points 3. i, ii, and iii above.)
4. It doesn't go far enough
Naturalists fail because they can't supply ontological foundations for what makes moral facts true, they offer a largely epistemological theory. But even here, Singer and Hauser are inadequate. They write, "over millions of years we have evolved a moral faculty that generates intuitions about right and wrong."
i) But for this "moral faculty" story to do any relevant work in ethical discussions about evolutionary justifications for moral realism, we must go farther. it is not enough that we have "a faculty," it must be a reliable faculty. If it unreliably generates intuitions, it is untrustworthy. So why believe that it is wrong rather than right to commit a holocaust? So, the faculty must be reliable.
ii) Not only must it be reliable, it must be functioning properly. Our "moral faculty" could reliably malfunction, and then what good would it be?
iii) Along with (i) and (ii), our faculty must be successfully aimed at producing true moral beliefs. It does no good if it functions properly and reliably at producing false moral beliefs.
(iv) Along with the above points, our faculty must also come equipped with a defeater system. See Sudduth.
But why think (i), (ii), (iii), and (iv) could plausibly have come about by way of natural selection?; a process, by the way, that keeps only what is needed for survival. Why think our "moral faculty" would be aimed at producing (mostly) true beliefs? Didn’t we learn from evolutionist Praticia Churchland that "truth, whatever that is, takes the hindmost" in these considerations? Didn't the evolutionist Francis Crick teach us that,
The Astonishing Hypothesis is that "You," your joys and your sorrows, your memories and your ambitions, your sense of personal identity and free will, are in fact no more than the behavior of a vast assembly of nerve cells and their associate molecules .... This hypothesis is so alien to the ideas of most people today that it can truly be called "astonishing" (Crick, The Astonishing Hypothesis, 1994, 3).Other evolutionists have also implicitly shed doubt on the idea that we can truth the product of natural selection to lead us into all truth. So Vizthum,
"A revised and modernized materialism concludes from all this that human thought and feeling is the product of a series of unthinking and unfeeling processes originated in the big bang.
"Materialism should no longer wink at such nonsense but insist that the foundations of all human thought and feeling are grossly irrational.
(Richard C Vitzthum, "Materialism: An Affirmative History and Definition," Prometheus Books, 1995, pp. 218-220.)
Of all these areas touched on, they fit much better in a Christian theistic worldview. Evolutionary moral theory doesn't seem to be scientifically grounded and is more speculatory than anything. It also doesn't seem to be able to explain how moral facts can be true. Indeed, it seems as if naturalistic anti-realists can "explain" facts without recourse to moral terms, and so it would seem simpler to do away with referring to moral terms. Singer and Hasuer at best tell us how we developed moral feelings. But, Singer and Hauser need to claim more for their "faculty," but once they do the further they get away from a naturalistic evolutionary worldview and the closer to a theistic one. A Christian theistic one I'd argue, but that's beyond the scope of the post. The above claim by Singer and Hauser is an oft repeated claim by atheists when called upon to account for morality. One analyzed a bit, it appears woefully inadequate.