40 IOWA ACADEMY OF SCIENCES. 



the species and the individuals which, by reason of their 

 power of adaptation, have not made the effort necessary 

 to seek out an environment similar to that in which their 

 ancestors had been living, will give rise to a modified race 

 of the species; this race will in most cases probably soon 

 overshadow their less variable relatives because of the 

 rapid increase rendered possible to them by small compe- 

 tition with other forms in the new environment. In other 

 words we- here have a method of isolation based primarily 

 on the efforts of the individuals to seek a favorable envi- 

 ronment, the result being polyphyletic evolution. 



In conclusion, I wish to say that I have made no attempt 

 to give a history of the different theories of heredity and 

 evolution that have in the past been proposed, to be either 

 ultimately accepted or rejected, but merely to select for 

 discussion a few leading ideas upon which attention has 

 been recently concentrated, and which seem to me to be 

 in the direct line of probable further advances in our 

 knowledge. 



