I. Haeckel and His Opponents

The human understanding has a tendency to imagine to itself that anything coming into existence was somehow already there, in some form or other, before its manifestation. The entire organism is supposed to be already hidden in the germ; the distinct organic classes, orders, families, species, and kinds are supposed to have existed as the thoughts of a creator before they actually came into existence. Now, however, the idea of evolution demands that we should conceive the arising of something new, of something later, from out of something already present, of something earlier. We are called upon to understand that which has become, out of the becoming. That we cannot do, if we regard all that has become as something which has always been there.