I. Haeckel and His Opponents

If we would explain organic forms after the same manner in which natural science deals with inorganic phenomena, we must demonstrate that the particular arrangement of the organisms—devoid of a purposeful object—comes into being by reason of what is practically natural necessity, even as one elastic ball after having been struck by another is fulfilling a law as it rolls along. This requirement has its fulfilment in Darwin's teachings regarding natural selection. Even in Nature organic forms must, in accordance with their capacity for assimilating modifications which have been brought about by artificial breeding, become transformed. Should there be nothing available for directly bringing about the change, so that none but the forms aimed at should come into existence, there will be, regardless of choice, useless, or less useful, forms called into being. Now, Nature is extremely wasteful in the bringing forth of her germs. So many germs are, indeed, produced upon our earth, that were they all to attain to development we should soon be able to fill several worlds with them.