Nature does nothing in vain

That is a maxim of the Schoolmen the moderns have carried over into the theory of evolution.

If over millions of years animals become more intelligent, more foresightful, more canny, these things must help.

But if the emergent view is right this should close the deal, should it not, for interactionism over epiphenomenalism?

Else natural selection would have no grip on these things but only on their physical causes, leaving the existence of these mental phenomena themselves wholly useless decor like fins on a 1960 Ford Galaxy.

Not impossible, no, any more than the Tooth Fairy.

But no better a fit, either, in the world as we otherwise know it.

Or think we do. 

So, interactionism, then?

That excludes physicalistic determinism but not psychological, the determination of one's choices by one's unchosen nature, character, and dispositions.

And certainly not logical.

And it entails, I think, philosophical swerve, in the sense of departures from or violations of purely physical, or chemical, or physio-chemical laws, as I think C. D. Broad pointed out so long ago.