Whence can arise the uniformity that is in all the works of animals? Why does each species invariably perform the same actions in the same manner? And why does not one individual perform them better or worse than another? Can there be a stronger proof that their operations are merely the effects of mechanism and materiality? If they possessed the smallest spark of that light which is inherent in mankind, their works would display variety at least, if not perfection, and one individual would, in its performance, make some little difference from what another had done. But this is far from being the case. One plan of action is common to the whole species, and whoever would attribute a mind or soul to animals, must of necessity allow but one to each species, of which each individual would be an equal partaker, and as thereby it would be divisible, it would consequently be material, and of a nature widely different from ours.
Why, on the other hand, are the productions and performances of men so various, and so diversified? Why is a servile imitation more troublesome to us than an original design? It is because our souls are our own, and independent of any other, and because we have nothing in common with our species but the matter which forms our body, and in which our resemblance to brute animals is confined.
Were internal sensations dependent on corporeal organs, should we not see as remarkable difference in the works of animals of the same species as in those of men? Would not those which were the most happily organized, build their nests and contrive their cells in a manner more solid, elegant, and commodious? And if any individual possessed a superior genius, would it not take an opportunity to manifest that superiority in its actions? But nothing of this kind has ever happened, and therefore the corporeal organs, however perfect or imperfect, have no influence on the nature of the internal sensations. Hence we may conclude, that animals have no sensations of this kind; that such sensations have no connection with matter, no dependence in their nature on the texture of corporeal organs, and that of consequence there must be a substance in man different from matter, which is the subject and the cause that produces and receives those sensations.
But these proofs of the immateriality of the human mind may be carried still farther. In all the works of nature there are imperceptible gradations maintained. This truth, which in no other instance admits of exception, is here expressly contradicted. Between the faculties of man and those of the most perfect animal the distance is infinite; an evident proof that man is of a different nature from the brute species, and that of himself he forms a distinct class, between which and that of animals there is an immense chasm. If man belonged to the class of animals, there would be a certain number of beings in nature less perfect than man, and more perfect than beast, in order to complete the gradation from a man to the monkey. But this is not the case; the transition is immediate from the thinking being to the material being; from intellectual faculties to mechanical powers; from order and design to blind motion; from reflection and choice to sensual appetite.
Enough has been here advanced to demonstrate the excellence of our nature, and of the immense distance which the bounty of the Creator has placed between man and the brute. The former is a rational being, the latter a being devoid of reason. And as there is no medium between the positive and the negative, between the rational and irrational being, it is evident that man is of a nature entirely different from that of the animal; that all the resemblance he bears to it is merely external; and that to judge of him by this resemblance, is wilfully to shut our eyes against that light, by which we ought to distinguish truth from falsehood.
Having thus considered man as to his internal properties, and proved the immateriality of his soul; we shall now proceed to examine his external part, and give the history of his body. We have already traced him from his formation to his birth, and after taking a view of the different ages of his life, we shall conduct him to that period when he must be separated from his body, and then resign him to the common mass of matter to which he belongs.