Stages in HMman Rvohition 



perature of the body rose. This Increased the 

 vigor of every function, but Its effect Is most 

 marked In the sensitive unstable material of the 

 brain. The warm-blooded animal, moving 

 swiftly through changing surroundings, began 

 to think. I suspect that the dawn of Intelligence 

 came far earlier, but In birds and mammals It Is 

 evident and unmistakable. 



Our history of the contributions made by 

 lower and earlier vertebrates to human structure 

 has been far too brief. Its brevity must not 

 blind us to the Importance and value of their 

 attainments. A tough, vigorous, flexible, com- 

 plex, and adaptable body was being framed, a 

 body which could endure rigorous hardships and 

 severe wounds, and which with a few modifica- 

 tions and additions could respond to all the de- 

 mands and execute the orders of a thinking 

 brain. 



Such changes and attainments could not be 

 made In a day. They lasted through the earlier 

 geological periods, when time was reckoned by 

 mlllenia or ages rather than by years. 



Protozoa were microscopic, worms were small, 

 the ancestral amphibians and reptiles were prob- 

 ably smaller than the average of their descend- 



