I tried writing this earlier, but my neighbor was playing Alanis Morissette music. I don’t ever think I’ve heard a woman play her music quietly. Anyway…
1) Our psychology is explained by the mechanisms described by contemporary evolutionary theory.
2) If our psychology is explained by the mechanisms described by contemporary evolutionary theory, then our behavior in moral situations is explained by natural selection (or genetic drift, spandrels, etc).
3) If our behavior in moral situations is explained by natural selection, then we don’t need independent moral facts to explain our behavior.
4) We don’t need independent moral facts to explain our behavior.
This is weak because it’s imprecise and empirically questionable. But, I think there is a good argument under here as long as you 1) are a strong-ish adaptationist and 2) you think something like evolutionary psychology is true. Let’s look at the premises:
(1): This is obviously a given. If you don’t care much for evolutionary theory, then the rest of the argument is uninteresting. But supposing you do, then you either think it explains some limited set of facts (not including our psychology) or all of the facts about us. Of course, evolutionary theory doesn’t explain why I am me and not someone else or other trivial logical truisms. But if evolutionary theory can explain anything, heritable behavior “dispositions” or traits are perfect candidates due to the immense visibility it would have for natural selection.
(2): I don’t really know what I mean by moral situations. I suppose it would be like our moral beliefs/judgments plus the other stuff going on in our heads. When I see some particularly heinous crime reported on television, I might find myself in an emotional state which culminates in some moral judgment: “Whoever did this deserves what’s coming to him.” Whatever relevant psychological states and factors are in such a moral moment, that’s specifically the sort of thing that would be visible to natural selection. I throw in a bit about genetic drift and spandrels for completeness’s sake, not because I think they are real contenders. Drift might work well in small populations, but our psychology and the underlying physical substructure that forms it are extremely complex and expensive resource-wise, and this is a telltale sign of the finagling of natural selection. One things to note here: Sharon Street, author of the paper inspiring this post, refers to “proto” traits as the heritable traits selected by evolutionary forces. Whether they are tendencies, beliefs (in proto form), judgments or dispositions is a little unclear. But one thing that is certain, she wisely wants to tread the line between blank-slate-ism and nativism, especially about content. We don’t want to think that, say, beliefs are inheritable. It must be something smaller. I would just say that they are judgment-forming faculties and leave it at that (or rather, punt to developmental psychologists).
(3): I don’t know if this is true or not. It seems true. If our psychology governs behavior and evolution explains behavior, then we don’t need moral facts to explain what happens in the real world. Think of it this way:
You: Why do humans protect their own children so viciously?
Me: [Evolutionary Explanation]
You: But also because it’s morally right?
Me: I dunno, maybe.
Of course, moral realism is logically compatible with this view, but it seems unlikely. Of course, this argument hinges on us actually caring that our psychology hooks up (or would hook up) with independent moral facts. You might be a weird error theorist and just claim that moral facts exist in Platonic heaven but it is of no consequence to us because our faculties were formed by the pressures of reproductive fitness, not rightness or wrongness.
