188 



THEORY OF EVOLUTION 



that is neither advantageous nor disadvanta- 

 geous, but indifferent, the chance that it may 

 become estabhshed 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 

 Pleuloeenc- 

 Upper Pliocene 



tL£PMAS 



Loter Pliocene TETRABEI.ODON < 



lLOWCIROSTKrs ST««1 

 Upper Miocene ishariaun^chinj 



Middle Miocene TETRA3EL0D0N 



(ANCiJSTIOrNS STACCl 



LoferMioeene (long chin j 



UppcrOtiyocene f<'9^">" f-"^ Afi'o 



" ^ inio tAininr ' Asia 



HuldleEocem 

 Ltmer Eocene 



1 . 



}MOERITHERIU 

 {^mrt dun) 



later Ob^oce ne '] 



PALAEOMASTODON 



l^prriocene [ C'"}^"""? ^^1 



m 



Fig. 93. Evolution of elei^hant's skulls. (After Dendy.) 



