212 Factors in Man's Evolution 



Twice I have moulded an image, 

 And thrice outstretched my hand, 

 Made one of day, and one of night, 

 And one of the salt sea-sand. 



It will be understood that the same sort of trying and 

 testing can be discerned in the story of the evolution 

 of other types, but the persistent pressing-on past 

 side-tracks and blind alleys touches us more when the 

 result is Man. 



§7. Factors in Man's Evolution. 



The not unfriendly criticism is sometimes made that 

 while the evidence undoubtedly suggests man's deri- 

 vation from a pre-human stock, the picture of what 

 may actually have occurred is very vague. This is 

 true in regard to most of the important big lifts in 

 evolution. We know very little about the factors that 

 were operative. 



It is not illegitimate to suppose that Homo arose 

 as a mutation, especially in the direction of a great 

 increase in the cerebral cortex. We do not know the 

 causes of mutations, but we know that they frequently 

 occur, and that when they appear they usually come 

 to stay. It is quite likely that the humanoid mutation 

 was associated with some great change in one or more 

 of the ductless or endocrinal glands, such as the 

 thyroid. 



There seems good sense in the idea that arboreal 

 apprenticeship on the part of Man's ancestors would 

 lead to very important changes. It led to the emanci- 

 pation of the hand, a new pose of body, a recession 



