20 FROM FISH TO PHILOSOPHER 



paleontologist technically calls preadaptation': the de- 

 velopment of characters that are apparently of no ad- 

 vantage under the circumstances in which they first 

 appear, but that prove to be highly advantageous under 

 new circumstances. In essence, it is simply putting old 

 (and sometimes not very useful) things to new uses un- 

 der new circumstances. 



Hence we cannot speak of those changes of climate 

 which have accompanied the geological revolutions of 

 the past as 'causing' the evolution of new and better- 

 adapted animals— the pressures of natural selection are 

 in no way recognized to be the causes of evolution. And 

 none of the vertebrate classes can certainly be shown 

 to have originated during a period of mountain build- 

 ing; with the possible exceptions of the reptiles and 

 mammals, new classes have appeared in the relatively 

 quiescent intervals separating mountain-building epi- 

 sodes. Nevertheless the pressure of natural selection 

 shapes evolution by turning its course here and there: 

 in the long view, evolution is adaptation, and if environ- 

 mental change did not occur coincidentally or subse- 

 quently, to foster or to give advantage to mutant forms, 

 variation would spend itself in vain and new and more 

 highly varied ways of life would have less probabihty 

 of coming into existence. 



Hence it is a vahd epitome to say that earth's turbulent 

 history has made us what we are. 



