The four roots

It is customary to regard the Sicilian Empedocles as a particularly archaic and reactionary thinker, but I believe that is a mistake. Like Parmenides, he wrote in hexameter verse, and he chose the language of myth. He adopted the Pythagorean idea of metempsychosis, and wrote of himself as a fallen daimon, one who had been ‘a bird, a bush, and a dumb sea-fish.’ Historians of science find it hard to take someone like that seriously. Nevertheless, he was responsible for three innovations of great importance to the history of science: the invention of elements, the postulation of two physical forces, qualitatively different from each other, and the first statement, so far as we know, of the concept of natural selection by survival of the fittest.

His theory of elements claimed that there are just four substances in the physical world: earth, water, air, and fire. There is a finite and unvarying quantity of each of them, and between them they make up all the material objects that there are, by mixing in different proportions. Empedocles gives an idea of how the theory works by offering a comparison with fourcolor painting: