ABSTRACT
Every organism has a long "phylogeny," or evolutionary history, behind it and many of its characteristics can be explained and understood only if we know the course its evolution has taken. Today we are well informed about the development of animals" physical characters thanks to research in comparative anatomy and the interpretation of fossil finds. The fact of evolution is generally acknowledged. But we are still debating whether the principle of mutation and selection is in itself sufficient to explain rapid evolution, or if we ought not to assume other additional evolutionary factors. The question also arises of whether some kind of direction-giving factors lie behind phylogenetic development and furthermore whether, in the field of behavior, one can assume a continuous evolutionary process right up to man himself.
