It seems clear to me that [most? any?] field that attempts to incorporate the deliverances of contemporary evolutionary theory will look a lot different after it does so than before. Epistemology and metaethics are two that have, in some way or another, had to face difficult questions posed by the intersection of deeply-held philosophical intuitions and established empirical fact. Can metaphysics be affected in the same manner? In short, no. Or, at least, depends. I think there can be a persuasive argument for anti-realism based on evolutionary psychology:
1) Our metaphysical beliefs are produced by our cognitive faculties.
2) Our faculties were formed by the ‘forces’ of contemporary evolutionary theory.
3) Contemporary evolutionary theory predicts that a trait is selected for behavioral reasons first and foremost, and may only happen to track truths.
4) If our metaphysical beliefs are behaviorally important, then we hold useful ones, not [necessarily] true ones.
5) If our metaphysical beliefs are not behaviorally important, then it is unlikely they just happen to track metaphysical truths.
6) Either way (5 or 6), we have a strong defeater for moral realism.
This argument depends on a few key assumptions. If you don’t think evolutionary forces played an interesting role in shaping how we think about specific things, then this might be a reach. If you think that the same faculties that navigates us through the world successfully (i.e. reproductive fitness) generates our metaphysical beliefs, then you might have a way out. But I take it that a serious commitment to contemporary evolutionary theory makes those two tenuous empirically.
Ok, so how does this cash out? Well, I take it that there are a few positions in logical space that one can have. On first glance, debates about composition seem shallow–I just don’t care about, nor do I think there is an interesting answer to, the question of whether an appletini is a martini (or whatever the hell that example is). But certainly there are some objective facts here. There are glasses and chemicals and alcoholics and all sorts of real things in the vicinity. So let’s just dispense with anti-realism and just let good arguments be good arguments and ignore trivial linguistic traps.
Two anti-realist responses. First, I take it that an anti-realist could say that there really are no facts of the matter in the vicinity that cash out into metaphysically interesting claims; sure, there are glasses per linguistic community, but not really. I’ll just assume that hyper-anti-realism is boring and wrong. The next thing an anti-realist could say is that of course there is a world and there is structure and facts of the matter about spacetime smears and abstract entities, but we could never know the answers. This is the sort of anti-realism that I think is hinted at by taking evolutionary psychology seriously. Certainly, it becomes difficult to see why should be able to answer these questions properly from a fitness-enhancing standpoint.
It’s late so I’ll continue this jumble of disjointed mind-dump later.