AGGREGATIONS OF HIGHER ANIMALS 1 1 7 



which the species cannot go with safety, and that in 

 some instances this is considerably above the theo- 

 retical minimum of one pair. 



By way of the laboratory, the coastal regions of 

 Massachusetts, and South African grassland and for- 

 est, we are arriving at a general biological principle 

 regarding the importance of numbers present on the 

 growth, survival and, as we shall see, upon the evolu- 

 tion of species of animals. 



Lacking definitive information on this last phase 

 of the subject, we shall turn to mathematical explo- 

 rations of its possibilities, as made primarily by Pro- 

 fessor Sewall Wright. (127, 41) Although the ideas to 

 be presented are essentially simple in principle, they 

 are sufficiently novel and unfamiliar to challenge the 

 closest attention. 



I shall not indulge here in the details of the mathe- 

 matical analyses, for the very good reason that I do 

 not understand them. If I were not convinced, how- 

 ever, that Professor Wright does understand them I 

 should not present this outline. It is only fair to say 

 that, in my opinion, in dealing with these ideal popu- 

 lations Professor Wright cannot bring into sharp 

 focus at one time all the factors that may be acting 

 in nature. This is what he Has been courageous 

 enough to attempt; the more nearly he succeeds, the 

 more likely is the calculation to be too complex for 



