Middle Cambrian Time Research Articles

Research Items

A Novel Theory of Animal Evolution. The problem presented by the inter-relationships between the major groups of animals has been the chief stumbling-block in the path of all theories of evolution. The enormous differences between these groups as they exist to-day make a linear evolution difficult to understand, and the difficulty is increased when it is realised that, so long ago as Middle Cambrian times, the inter-relation- ships between the different invertebrate phyla were just the same as they are to-day. Austin H. Clark therefore suggests that at the very outset all the numerous phyla came into being not successively but simultaneously by following different paths of develop- ment from the single cell and to this theory he gives the name primagenesis (Jour. Washington Acad. i., vol. 10, June 1929). The abrupt discontinuities suggest that each of the phyla represents a re-combination of characters inherent in animals as a whole in a form capable of meeting the requirements of animal exist- ence, both in internal balance and in external contacts. Apparently the focal points at which a balanced con- dition capable of survival and of meeting competition is attainable are rather few and are well separated from each other, for each of the phyla is widely different from the rest. The flat picture of animal life presented as a result of primagenesis serves as the ground from which various evolutionary trees, one for each phylum, rise upwards through geological time.