PRE-CAMBRIAN FAUNAS 123 



differentiation of all the main phyletic stocks. The 

 simple qualities shown by most Lower Cambrian 

 organisms imply that the phyla were but newly 

 specialized at that time. Perhaps some ancestral 

 Metazoan stock had branched, almost at a single node, 

 into the various phyla, at a stage not much more remote 

 than the upper pre-Cambrian. Prior to this episode, 

 comparable acceleration may have differentiated the 

 three great sections of the animal kingdom within a 

 relatively brief period. 



It may be objected that the foregoing hypothesis is 

 reactionary, in that it revives conceptions which, in 

 geological discussions, have been discarded as unsound. 

 Early schools of Geologists introduced ideas of the 

 acceleration of physical processes in remote periods, 

 largely under the (subconscious) pressure of theological 

 prejudice. According to their beliefs, rain fell more 

 heavily, rivers flowed more swiftly, and the sea (perhaps 

 "boiling-hot") was more rapacious then than now, so 

 that vast quantities of rock-matter were eroded and 

 deposited during short intervals of time. All of which 

 is not proven and difficult of belief. But arguments for 

 organic acceleration fall into a different category. All 

 available evidence points to the vigour and variability 

 of youth, whether individual or racial. It is not mere 

 speculation, but construction of a hypothesis based on 

 observed phenomena, to suggest that differentiation and 

 evolution of organisms may have proceeded rapidly 

 (measured by later standards) "when the world was 

 young." 



