General Conclusions. 147 



OF ANOTHER FORM IN ORDER TO CREATE AN 

 ADDITIONAL CASE OF ISOLATION, OR TO CAUSE 

 POLYTYPIC AS DISTINGUISHED FROM MONOTYPIC 

 EVOLUTION. 



II. Where common areas and polytypic evo- 

 lution ARE concerned, THE MOST GENERAL AND 

 MOST EFFICIENT FORM OF ISOLATION HAS BEEN 

 THE PHYSIOLOGICAL, AND THIS WHETHER THE 

 MUTUAL INFERTILITY HAS BEEN THE ANTECEDENT 

 OR THE CONSEQUENT OF MORPHOLOGICAL CHANGES 

 ON THE PART OF THE ORGANISMS CONCERNED, AND 

 WHETHER OR NOT THESE CHANGES ARE OF AN 

 ADAPTIVE CHARACTER. 



la. This form of isolation— which, in 

 regard to incipient species, i have called 

 Physiological Selection — may act either 

 alone or in conjunction with other forms of 



isolation on common AREAS : IN THE FORMER 

 CASE ITS AGENCY IS OF MOST IMPORTANCE AMONG 

 PLANTS AND THE LOWER CLASSES OF ANIMALS ; 

 IN THE LATTER CASE ITS IMPORTANCE CONSISTS 

 IN ITS GREATLY INTENSIFYING THE SEGREGATIVE 

 POWER OF WHATEVER OTHER FORM OF ISOLATION 

 IT MAY BE WITH WHICH IT IS ASSUCIAi ED. 



L I 



