THE GROWTH OF GROUPS 129 



be taken in order to prevent a mutant from growing into 

 a species. 



Tower states his objection to the origin of species from 

 mutants plainly. He does not believe that mutants 

 would get a start in nature, since wherever he looked the 

 commonest mutant, pattida, was not becoming established. 

 Hence he concluded that it was impossible for it and all 

 other mutants to become established. But it seems to 

 me that this conclusion is unjustifiable. It seems un- 

 generous to speak of Mr. Tower's observations as small, 

 since in comparison with other human observations they 

 are great indeed, but we cannot overlook the fact that 

 the species decemlineata, as it lies spread over more than 

 half of the United States, is an immense thing of which 

 a small fraction was seen. The area of distribution of 

 the species is certainly large, and the beetle is very common 

 in some places ; a fact that is illustrated by the following 

 quotation from the letter of a farmer in Kansas, written 

 in 1862, and quoted by Tower. "It is no exaggeration 

 when I tell you that we have often in a very short time 

 gathered as many as two bushels of them." If a cubic 

 inch contains ten beetles, a bushel will contain over 

 twenty thousand. It seems evident then that the popu- 

 lation of potato beetles in the United States, like the house 

 rats in India, must be recognized in thousands of millions. 

 But the actual number of beetles examined for sports 

 was less than a quarter of a million, that is a small fraction 

 of the whole. Is it then justifiable to conclude that a group 

 of pallida could not get a start either now or within the 

 next few hundred years ? is it a sound deduction from the 

 observations made in the particular case, let alone the living 

 kingdom in general ? The reader must form his own opinion. 



