40 THE BIOCOSMOS GENERAL INTRODUCTION. 



tween the organisms containing the lowest 

 and highest human intelligence. Such is the 

 most significant turning point in the entire 

 stretch of animal evolution: the change from 

 a physical to a psychical plasticity, which al- 

 ready began to show itself decisively in the 

 era of the anthropoids. 



In order to get the bearing of this subject, 

 it is worth while to go back and mark the 

 most important nodes of the evolutionary as- 

 cent of living shapes. Very sharply is it rec- 

 ognized that man has a vertebral column in 

 common with a long ancestral line down to 

 the Fishes. We may start with that portion 

 of the animal kingdom now called the Chor- 

 dates, from their distinctive member known 

 as the notochord. Of these the vertebrates 

 are a division whose beginning is usually 

 placed far back in the Devonian age. But 

 when did that vertebrated fish begin, or how ? 

 Doubtless in the sea, and man still shows in 

 his organism traces of having once lived in 

 the water, where his backbone first started in 

 its primal simplicity. But the next great 

 node in the evolution of the vertebrate animal 

 was when it became a mammal, evolving the 

 mammary gland specially in the female 

 which probably took place in the Carbonif- 

 erous era, estimated variously from ten to 

 fifty millions of years ago. Again we have 



