ARISTOTLE VS. EMPEDOCLES ON EVOLUTION
EMPEDOCLES' THEORY OF EVOLUTION (Aristotle, Physics II.8)
  • Why should not nature work as the sky rains, not in order to make the corn grow, but of necessity? Similarly if the crop is spoiled on the threshing-floor, the rain did not fall for the sake of this--in order that the crop might be spoiled--but that result just followed. Why should it not be the same with the parts in nature, e.g. that teeth should come up of necessity--the front teeth sharp, fitted for tearing, the molars broad and useful for grinding down the food--since they did not arise for this end, but it was merely a coincidental result; and so with all other parts in which we suppose there is purpose? Wherever then all the parts came about just what they would have been if they had come be for an end, such things survived, being organized spontaneously in a fitting way; whereas those which grew otherwise perished and continue to perish, as Empedocles says his 'man-faced ox-progeny' did.
    • Notice that Empedocles included both of the key elements of evolution in his theory:
  • The concept of random mutation, i.e. that 'parts' came about by chance: they did not arise for this end, but it was merely a coincident result.
  • The concept of natural selection, i.e. that some of the evolving things which came about by chance were better fitted to survive in their environment, and these and their progeny survived, while the unfit and their kind perished: Wherever then all the parts came about just what they would have been if they had come be for an end, such things survived, being organized spontaneously in a fitting way; whereas those which grew otherwise perished and continue to perish, as Empedocles says his 'man-faced ox-progeny' did.
    • ARISTOTLE'S ARGUMENTS AGAINST EMPEDOCLEAN EVOLUTION
    1. The argument from normalcy
            Aristotle argues that teleological structures, such as teeth, cannot have evolved, because they invariably or normally come about a given way; but the results of chance do not come about in that regular manner.
  • If then, things are either (a) the result of coincidence or (b) for an end, and these cannot be the result of coincidence or spontaneity, it follows that they must be for an end.
    • 2. The argument from goal-directed behavior
            Aristotle argues that telelogical behavior, such as spiders weaving webs or plants sending out roots, do not come about by chance, because the preceding steps are for the sake of the end.
  • If then it is by nature and for an end that the swallow makes its nest and the spider its web and plants grow leaves for the sake of the fruit and send out roots for nourishment, it is plain this kind of cause is operative in things which come to be and are by nature.
    • 3. The argument from mistakes or monstrosities
            Aristotle argues that in nature, as in art, where mistakes occur there was a purpose in what was attempted, only it was not attained, so monstrosities are failures in the purposive effort.
  • Thus in the original combinations the 'ox-progeny' if they failed to reach a determinate end must have arisen through the corruption of some principle corresponding to what is now the seed.

    • Evaluate Aristotle's arguments vs. Empedoclean proto-evolutionary theory.