Pre-Darwinian Evolutionists-Causes which led to the speedy triumph of the theory of Natural Selection-Nature of the opposition which Darwin had to overcome-Post-Darwinian biology-Usually accepted classification of present-day biologists as Neo-Lamarckians and Neo-Darwinians is faulty-Biologists fall into three classes rather than two-Neo-Lamarckism: its defects-Wallaceism: its defects-Neo-Darwinism distinguished from Neo-Lamarckism and Wallaceism-Neo-Darwinism realises the strength and weakness of the theory of Natural Selection, recognises the complexity of the problems which biologists are endeavouring to solve. Darwinism and evolution are not interchangeable terms. On this fact it is impossible to lay too much emphasis. Charles Darwin was not the originator of the theory of evolution, nor even the first to advocate it in modern times. The idea that all existing things have been produced by natural causes from some primordial material is as old as Aristotle. It was lost sight of in the mental stagnation of the Middle Ages. In that dark period zoological science was completely submerged. It was not until men shook off the mental lethargy that had held them for many generations that serious attention was paid to biology. From the moment when men began to apply scientific methods to that branch of knowledge the idea of evolution found supporters.