Mr. Derbyshire makes this riposte rather nicely, and I am glad to note that it is right along the lines I was arguing yesterday:

Human agency indeed causes many things to happen — books to be written, flints to be knapped, and so on. That human agency arises from non-material origins is, however, a metaphysical hypothesis, outside the purview of science. When an anthropologist, via material evidence, has tracked an artifact back to human agency, he ceases his enquiries. (Unless he has a night job as a neuroscientist, in which case he might proceed further.) That is the scope of anthropology. It is the study of human communities and their artifacts. An anthropologist is no more concerned with the neurophysiological, possibly non-material, springs of human action than a chemist is with String Theory, or a geologist with cosmology. It’s not his scope. It is news to me that anthropologists, paleo- or otherwise, necessarily regard human agency as having non-material sources. My guess would be that some anthropologists do, some don’t. If a purely materialistic explanation for human nature were to be irrefutably established tomorrow, it does not seem to me that anthropology would thereupon implode, or cease to be practiced. I am not an anthropologist, however, and will humbly take contradiction from any reader who is. ~John Derbyshire, Out of the Corner