Before the theory of evolution by natural selection was well-known, it seems that the usefulness of our organs was explained in two major ways. Either (a) they were designed for the purpose or fulfilling the ends that we achieve with them, or (b) they arose through mindless means and, after this, we discovered that they were useful for certain purposes and began to use them for those purposes.
The latter was argued by Lucretius in the following passage:
Herein you must eagerly desire to shun this fault, and with foresighted fear to avoid this error; do not think that the bright light of the eyes was created in order that we may be able to look before us, or that, in order that we may have power to plant long paces, therefore the tops of shanks and thighs, based upon the feet, are able to bend; or again, that the forearms are jointed to the strong upper arms and hands given us to serve us on either side, in order that we might be able to do what was needful for life. All other ideas of this sort, which men proclaim, by distorted reasoning set effect for cause, since nothing at all was born in the body that we might be able to use it, but what is born creates its own use. Nor did sight exist before the light of the eyes was born, nor pleading in words before the tongue was created, but rather the birth of the tongue came long before discourse, and the ears were created much before sound was heard, and in short all the limbs, I trow, existed before their use came about: they cannot then have grown for the purpose of using them. But, on the other side, to join hands in the strife of battle, to mangle limbs and befoul the body with gore; these things were known long before gleaming darts flew abroad, and nature constrained men to avoid a wounding blow, before the left arm, trained by art, held up the defence of a shield. And of a surety to trust the tired body to rest was a habit far older than the soft-spread bed, and the slaking of the thirst was born before cups. These things, then, which are invented to suit the needs of life, might well be thought to have been discovered for the purpose of using them. But all those other things lie apart, which were first born themselves, and thereafter revealed the concept of their usefulness. In this class first of all we see the senses and the limbs; wherefore, again and again, it cannot be that you should believe that they could have been created for the purpose of useful service.
This, likewise, is no cause for wonder, that the nature of the body of every living thing of itself seeks food. For verily I have shownn that many bodies ebb and pass away from things in many ways, but most are bound to pass from living creatures. For because they are sorely tried by motion and many bodies by sweating are squeezed and pass out from deep beneath, many are breathed out through their mouths, when they pant in weariness; by these means then the body grows rare, and all the nature is undermined; and on this follows pain. Therefore food is taken to support the limbs and renew strength when it passes within, and to muzzle the gaping desire for eating through all the limbs and veins. Likewise, moisture spreads into all the spots which demand moisture; and the many gathered bodies of heat, which furnish the fires to our stomach, are scattered by the incoming moisture, and quenched like a flame, that the dry heat may no longer be able to burn our body. Thus then the panting thirst is washed away from our body, thus the hungry yearning is satisfied.
— On the Nature of Things, book IV, 823–76
William Paley took the time to argue against this opinion in the following section:
To the marks of contrivance discoverable in animal bodies, and to the argument deduced from them, in proof of design, and of a designing Creator, this turn is sometimes attempted to be given, viz. that the parts were not intended for the use, but that the use arose out of the parts. This distinction is intelligible. A cabinet-maker rubs his mahogany with fish-skin;* yet it would be too much to assert that the skin of the dog fish was made rough and granulated on purpose for the polishing of wood, and the use of cabinet-makers. Therefore the distinction is intelligible. But I think that there is very little place for it in the works of nature. When roundly and generally affirmed of them, as it hath sometimes been, it amounts to such another stretch of assertion, as it would be to say, that all the implements of the cabinet-maker’s workshop, as well as his fish-skin, were substances accidentally configurated, which he had picked up, and converted to his use; that his adzes, saws, planes, and gimlets, were not made, as we suppose, to hew, cut, smooth, shape out, or bore wood with; but that, these things being made, no matter with what design, or whether with any, the cabinet-maker perceived that they were applicable to his purpose, and turned them to account.
But, again; so far as this solution is attempted to be applied to those parts of animals the action of which does not depend upon the will of the animal, it is fraught with still more evident absurdity. Is it possible to believe that the eye was formed without any regard to vision; that it was the animal itself which found out, that, though formed with no such intention, it would serve to see with; and that the use of the eye, as an organ of sight, resulted from this discovery, and the animal’s application of it? The same question may be asked of the ear; the same of all the senses. None of the senses fundamentally depend upon the election of the animal: consequently neither upon his sagacity, nor his experience. It is the impression which objects make upon them that constitutes their use. Under that impression he is passive. He may bring objects to the sense, or within its reach; he may select these objects; but over the impression itself he has no power, or very little; and that properly is the sense.
Secondly, there are many parts of animal bodies which seem to depend upon the will of the animal in a greater degree than the senses do, and yet with respect to which this solution is equally unsatisfactory. If we apply the solution to the human body, for instance, it forms itself into questions upon which no reasonable mind can doubt; such as, whether the teeth were made expressly for the mastication of food, the feet for walking, the hands for holding; or whether, these things being as they are, being in fact in the animal’s possession, his own ingenuity taught him that they were convertible to these purposes, though no such purposes were contemplated in their formation.
All that there is of the appearance of reason in this way of considering the subject is, that, in some cases, the organization seems to determine the habits of the animal, and its choice, to a particular mode of life; which, in a certain sense, may be called ‘the use arising out of the part.’ Now to all the instances, in which there is any place for this suggestion, it may be replied, that the organization determines the animal to habits beneficial and salutary to itself; and that this effect would not be seen so regularly to follow, if the several organizations did not bear a concerted and contrived relation to the substances by which the animal was surrounded. They would, otherwise, be capacities without objects; powers without employment. The web foot determines, you say, the duck to swim: but what would that avail, if there were no water to swim in? The strong, hooked bill, and sharp talons, of one species of bird, determine it to prey upon animals; the soft straight bill, and weak claws, of another species, determine it to pick up seeds: but neither determination could take effect in providing for the sustenance of the birds, if animal bodies and vegetable seeds did not lie within their reach. The peculiar conformation of the bill, and tongue, and claws of the woodpecker, determines that bird to search for his food amongst the insects lodged behind the bark, or in the wood, of decayed trees; but what would this profit him if there were no trees, no decayed trees, no insects lodged under their bark, or in their trunk? The proboscis with which the bee is furnished, determines him to seek for honey; but what would that signify, if flowers supplied none? Faculties thrown down upon animals at random, and without reference to the objects amidst which they are placed, would not produce to them the services and benefits which we see: and if there be that reference, then there is intention.
Lastly, the solution fails entirely when applied to plants. The parts of plants answer their uses, without any concurrence from the will or choice of the plant.
It is interesting to me to see how entirely the state of this question was changed by the introduction of natural selection. I don’t know if there had been more sophisticated arguments on either side back then, but it seems to me that the Lucretian side was clearly disadvantaged in that state of human knowledge. Our organs are just too convenient; it seems clearly motivated to simply dismiss their obvious “appearance of having been designed for a purpose” in this way; and coming from an Epicurean, we might easily think that the motivation was to excuse for his impiety and hedonism.
Update 2021-07-05: To add another reference that I just saw, the same two alternatives are presented in the introduction to William Ogle’s 1882 edition of Aristotle’s Parts of Animals.
No comments:
Post a Comment