Among the substantial beings constituted by nature, some are ungenerated and imperishable throughout all eternity [stuff in the heavens, the stars and planets, the celestial], while others partake of generation and perishing [stuff on earth, the terrestrial]. Yet it has turned out that our studies of the former, though they are valuable and divine, are fewer (for as regards both those things on the basis of which one would examine them and those things about them which we long to know, the perceptual phenomena are all together few). We are, however, much better provided in relation to knowledge about the perishable plants and animals, because we live among them. For anyone wishing to labour sufficiently can grasp many things about each kind. Each study has its attractions. Even if our contact with eternal [celestial] beings is slight, none the less because of it surpassing value this knowledge is a greater pleasure than our knowledge of everything around us, even as a chance, brief glimpse of the ones we love is a greater pleasure than seeing accurately many other and great things. Perishable [terrestrial] beings, however, take the prize in respect of understanding because we know more of them and we know them more fully. Further, because they are nearer to us and more of our own nature, they provide a certain compensation compared with the philosophy concerned with divine things.
Since we have completed stating the way things appear to us about the divine things, it remains to speak about animal nature, omitting nothing in our power, whether of lesser or greater esteem. For even in the study of animals disagreeable to perception, the nature that crafted them likewise provides extraordinary pleasures to those who were able to know their causes and are by nature philosophers. Surely it would be unreasonable, even absurd, for us to enjoy studying likenesses of animals – – on the ground that we are at the same time studying the art, such as painting or sculpture, that made them – – while not prizing even more the study of things constituted by nature, at least when we can behold the causes.
For this reason we should not be childishly disgusted at the examination of the less valuable animals. For in all natural things there is something marvelous. Even as Heraclitus is said to have spoken to those strangers who wished to meet him but stopped as they were approaching when they saw him warming himself by the oven – – he bade them enter without fear, ‘for there are gods here too’ – – so too one should approach research about each of the animals without disgust, since in every one there is something natural and good. For what is not haphazard but rather for the sake of something is in fact present most of all in the works of nature; the end for the sake of which each animal has been constituted or comes to be takes the place of the good. If someone has considered the study of the other animals to lack value, he ought to think the same thing about himself as well; for it is impossible to look at that from which mankind has been constituted – – blood, flesh, bones, blood vessels, and other such parts – – without considerable disgust. Just as one who discusses the parts or equipment of anything should not be thought of as doing so in order to draw attention to the matter, nor for the sake of the matter, but rather in order to draw attention to the overall shape (e.g. to a house rather than bricks, mortar, and timbers); likewise one should consider the discussion of nature to be referring to the composite and the overall substantial being rather than to those things which do not exist when separated from their substantial being.
–Aristotle, Parts of Animals, Chapter 5, Book 1 (translator Jim Lennox)