Man Not Fundamentally Different From the Animals, 1775

Browsing eighteenth-century philosophy of mind, and science of mind more generally, it is striking how often one comes upon thoughts that Victorianists like to argue only began being articulated post Darwin.  Here's Priestley's Hartley's Theory of the Human Mind, on the Principle of the Association of Ideas (1775).  The soul is a material function of the brain, not an immaterial 'spirit' somehow attached to a material brain.

It will stagger some persons, that so much of the business of thinking should be made to depend upon mere matter, as the doctrine of vibrations supposes. For, in fact, it leaves nothing to the province of any other principle, except the simple power of perception; so that if it were possible that matter could be endued with this property, immateriality, as far as it has been supposed to belong to man, would be excluded altogether. But I do not know that this supposition need give any concern, except to those who maintain that a future life depends upon the immateriality of the human soul. It will not at all alarm those who found all their hopes of a future existence on the Christian doctrine of a resurrection from the dead.

It has been the opinion of many philosophers, and among others of Mr. Locke, that for any thing that we know to the contrary, a capacity of thinking might be given to matter. Dr. Hartley, however, notwithstanding his hypothesis would be much helped by it, seems to think otherwise. He also supposes that there is an intermediate elementary body between the mind and the gross body; which may exist, and be the instrument of giving pleasure or pain to the sentient principle after death. But I own I see no reason why his scheme should be burdened with such an incumbrance as this.

I am rather inclined to think that, though the subject is beyond our comprehension at present, man does not consist of two principles, so essentially different from one another as matter and spirit, which are always described as having not one common property, by means of which they can affect or act upon each other; the one occupying space, and the other not only not occupying the least imaginable portion of space, but incapable of bearing relation to it; insomuch that, properly speaking, my mind is no-more in my body, than it is in the moon. I rather think that the whole man is of some uniform composition, and that the property of perception, as well as the other powers that are termed mental, is the result (whether necessary or not) of such an organical structure as that of the brain. Consequently, that the whole man becomes extinct at death, and that we have no hope of surviving the grave but what is derived from the scheme of revelation. Our having recourse to an immaterial principle, to account for perception and thought, is only saying in other words, that we do not know in what they consist; for no one will fay that he has any conception how the principle of thought can have any more relation to immateriality than to materiality.

This hypothesis is rather favourable to the notion of such organical systems as plants having some degree of sensation. But at this a benevolent mind will rather rejoice than repine. It also makes the lower animals to differ from us in degree only, and not in kind, which is sufficiently agreeable to appearances; but does not necessarily draw after it the belief of their surviving death, as well as ourselves; this privilege being derived to us by a positive constitution, and depending upon the promise of God, communicated by express revelation to man.