Buffon's Natural History. Volume 05 (of 10) / Containing a Theory of the Earth, a General History of Man, of the Brute Creation, and of Vegetables, Minerals, &c. &c

by comte de Georges Louis Leclerc Buffon

Confined solely to that part which acts continually, the most perfect animal will not appear to differ from those beings to which we can scarcely give the appellation of animal. As to external functions, it would be nearly upon a level with a vegetable; for however different the internal organization of animals and vegetables may be, the inferences will be the same. They each receive nourishment, grow, expand, have external motions, and a vegetating life. But of progressive motion, action, and sentiment, they will be equally destitute; nor be endowed with any interior or apparent character by which animal life may be distinguished. Investing, however, this internal part with senses and members, animal life will presently manifest itself; and the more this cover shall contain of sense and members, the more will the animal life be perfect. It is by this investment that animals differ from each other. The internal part belongs, without exception, to all animals; and is nearly the same in all which have flesh and blood. The external cover, however, is widely different; and it is at its extremities that the greatest differences subsist.

In order to elucidate this argument, let us compare the body of a man with that of a horse or an ox. In each the heart and lungs, or the organs of circulation, and of respiration, are nearly the same; but the external cover is highly different. The materials of the animal body, though the parts are similar to those of the human, vary greatly as to number, size, and position; and thereby the dissimilitudes in their respective forms are rendered very wide. Besides, we shall find that the greatest differences are at the extremities; for in dividing the body into three principal parts, the trunk, the head, and the members, we find, that in the head and members, which are the extremities of the body, consist, the most material difference between man and other animals. We discover that the greatest difference in the trunk is at the two extremities; since in men there are clavicles at the upper extremity, which in animals are wanting; and the under extremity of animals is terminated by a tail, consisting of a certain number of exterior vertebræ, which the human body is without. The inferior extremity of the head also, as the jawbones, and the upper extremity, as the bones the forehead, differ prodigiously in man and beast. Finally, by comparing the members of a man with those of other animals, we plainly perceive it is at the extremities they differ most, as no two things bear less resemblance to each other, than the human hand with the foot of a horse or an ox.

Taking the heart then for the centre of the animal machine, we find in that and other adjacent parts, there is a perfect resemblance between man and other animals: but the more we remove from this centre, the more they become different; and when in the centre itself there is found any difference, then the animal is infinitely more distant from man, and possesses nothing in common with those animals we are now considering. In most insects, for example, there is a peculiar organization of this principal part of the animal economy. Instead of heart and lungs, they have parts which, being subservient to the vital functions, have been considered as analogous to those viscera, but which in reality widely differ from them, both in structure and result of action, and therefore are insects to the last degree different from man and other animals. A minute difference in the centrical parts is always accompanied with an infinitely greater in the exterior parts. The tortoise, whose heart is of a peculiar structure, is a very extraordinary animal, and has not the smallest resemblance to any other animated being.

In considering men, quadrupeds, birds, cetaceous animals, fishes, reptiles, &c. what prodigious variety do we find in the figure and proportion of their bodies, in the number and position of their members, in the substance of their flesh and bones? Quadrupeds have generally tails and horns; cetaceous animals live in another element, and though their mode of generation is similar to that of quadrupeds, yet they differ greatly from them in form, having no inferior extremities; birds differ still more by their beaks, feathers, wings, and their propagation by eggs; fishes and amphibious animals are yet farther removed from the human form, and reptiles have no members. In the whole exterior covering there is the greatest diversity, the interior conformation being nearly the same; they have all a heart, a liver, a stomach, intestines, and organs for generation; these ought to be considered as parts the most essential to the animal economy, since they are the most fixed, and least subjected to variation.

But it is to be observed that, even in the cover, there are some parts more fixed than others. Of all the senses none of these animals are divested. We have already explained what may be their sensation of feeling. What may be the nature of their smelling and taste we know not, but we are assured they all enjoy the sense of seeing, and perhaps that of hearing also. The senses may be considered, then, as another essential part of the animal economy, as well as the brain, from which sensation derives its origin. Even insects, which differ so much in the centre of the animal economy, have a part analogous to the brain, and its functions resemble those of other animals; and such as the oyster, which seems to be deprived of a brain, ought to be considered as only half-animated, and as filling up an intermediate space between the animal and the vegetable kingdoms.

As the heart is the centre of the interior part of the animal, so is the brain the centre of the cover. In like manner as the heart, and all the interior parts, communicate with the brain and exterior cover, by means of the blood-vessels, the brain communicates with the heart, and with all the interior parts, by means of the nerves. This union appears to be intimate and reciprocal, and though of these two organs the functions are absolutely different, yet they can never be separated without the instant death of the animal.

The heart and the whole interior part acts continually without interruption, and independent of any exterior cause; but the senses and exterior part act only by alternate intervals, when affected by external causes. Objects act upon the senses, the senses modify this action, and carry the impression modified into the brain, where it becomes what we term sensation. In consequence of this impression the brain acts on the nerves, and communicates the vibration it has received; and this vibration it is which produces progression, and all the other exterior actions of the body. Whenever a cause acts upon a body, we know that the body also acts upon the cause. Thus objects act upon animals by means of the senses, and animals act upon the object by its exterior movements. In general action is the cause, and re-action the effect.

It may be said, that in solid bodies, which follow the laws of mechanism, the re-action is always equal to the action; but that in the animal body it appears that the re-action is greater than the action, and that the other exterior movements ought not to be considered as simple effects of the impression of objects upon the senses. To this objection I reply, that though in certain cases effects appear proportioned to their causes, there is in Nature an infinite number of cases where the effects bear no kind of proportion to their apparent causes. By a single spark of fire a magazine of powder may be set in flame, and a citadel be blown up. By electricity a slight friction produces a violent shock, which is communicated to great distances, and if a thousand persons touch each other, they would all be almost as much affected by it as if the shock had been confined to each of them individually. It is not, then, extraordinary that a slight impression on the senses should produce in the animal body a violent re-action, and should manifest itself by exterior movements.

The causes we are qualified to ascertain, and the quantity of whose effects we can precisely estimate, are less numerous than those whose mode of action is unknown, and of whose proportional relation with their effects, we are entirely ignorant. Now most effects in Nature depend on a number of causes differently combined, whose actions vary, and seem to be determined by no established law, consequently we can only form a conjectural estimate by endeavouring to approximate the truth by the means of probabilities.

I pretend not, then, to assert as a demonstrative fact, that progressive and other exterior movements of animals, are caused solely by the impression of objects upon the senses. I mention it merely as likely, and founded on principles of analogy, since all organized beings, which are destitute of sense, are likewise destitute of progressive motion, and that all those which possess the one have also the other.