188 



THEORY OF EVOLUTION 



that is neither advantageous nor disadvanta- 

 geous, but indifferent, the chance that it may 

 become established in the race is extremely 

 small, although by good luck such a thing may 

 occur rarely. It makes no difference whether 

 the character in question is a dominant or a 



Recent 



tamer Pliocene TETRABELODON 

 Upper Miocene 



Middlr Miocene TETRABELOOON 



(ANCUSTIOENS STACX) 

 Loner Miocene (Imyctiin) 



turoftr -Ana 



Otiyocene'} 

 rlacene \ 



PALAEOMASTODON 

 UpptrEoctne \ f'-J*""f *"/ 



FIG. 93. Evolution of elephant's skulls. (After Dendy.) 



