(12) Earthquakes were caused by the air above striking on that beneath the earth; for the movement of the latter caused the earth which floats on it to rock.
All this confirms in the most striking way the statement of Theophrastos, that Anaxagoras had belonged to the school of Anaximenes. The flat earth floating on the air, the dark bodies below the moon, the explanation of the solstices and the “turnings” of the moon by the resistance of air, the explanations given of wind and of thunder and lightning, are all derived from the earlier inquirer.
Biology.
136. “There is a portion of everything in everything except Nous, and there are some things in which there is Nous also” (fr. [11]). In these words Anaxagoras laid down the distinction between animate and inanimate things. He tells us that it is the same Nous that “has power over,” that is, sets in motion, all things that have life, both the greater and the smaller (fr. [12]). The Nous in living creatures is the same in all (fr. [12]), and from this it followed that the different grades of intelligence which we observe in the animal and vegetable worlds depend entirely on the structure of the body. The Nous was the same, but it had more opportunities in one body than another. Man was the wisest of animals, not because he had a better sort of Nous, but simply because he had hands.[[718]] This view is quite in accordance with the previous development of thought upon the subject. Parmenides, in the Second Part of his poem (fr. [16]), had already made the thought of men depend upon the constitution of their limbs.
As all Nous is the same, we are not surprised to find that plants were regarded as living creatures. If we may trust the pseudo-Aristotelian Treatise on Plants[[719]] so far, Anaxagoras argued that they must feel pleasure and pain in connexion with their growth and with the fall of their leaves. Plutarch says[[720]] that he called plants “animals fixed in the earth.”
Both plants and animals originated in the first instance from the πανσπερμία. Plants first arose when the seeds of them which the air contained were brought down by the rain-water,[[721]] and animals originated in a similar way.[[722]] Like Anaximander, Anaxagoras held that animals first arose in the moist element.[[723]]
137. In these scanty notices we seem to see traces of a polemical attitude towards Empedokles, and the same may be observed in what we are told of the theory of perception adopted by Anaxagoras, especially in the view that perception is of contraries.[[724]] The account which Theophrastos gives of this[[725]] is as follows:—
But Anaxagoras says that perception is produced by opposites; for like things cannot be affected by like. He attempts to give a detailed enumeration of the particular senses. We see by means of the image in the pupil; but no image is cast upon what is of the same colour, but only on what is different. With most living creatures things are of a different colour to the pupil by day, though with some this is so by night, and these are accordingly keen-sighted at that time. Speaking generally, however, night is more of the same colour with the eyes than day. And an image is cast on the pupil by day, because light is a concomitant cause of the image, and because the prevailing colour casts an image more readily upon its opposite.[[726]]
It is in the same way that touch and taste discern their objects. That which is just as warm or just as cold as we are neither warms us nor cools us by its contact; and, in the same way, we do not apprehend the sweet and the sour by means of themselves. We know cold by warm, fresh by salt, and sweet by sour, in virtue of our deficiency in each; for all these are in us to begin with. And we smell and hear in the same manner; the former by means of the accompanying respiration, the latter by the sound penetrating to the brain, for the bone which surrounds this is hollow, and it is upon it that the sound falls.[[727]]
And all sensation implies pain, a view which would seem to be the consequence of the first assumption, for all unlike things produce pain by their contact. And this pain is made perceptible by the long continuance or by the excess of a sensation. Brilliant colours and excessive noises produce pain, and we cannot dwell long on the same things. The larger animals are the more sensitive, and, generally, sensation is proportionate to the size of the organs of sense. Those animals which have large, pure, and bright eyes, see large objects and from a great distance, and contrariwise.[[728]]