Analysis of Heterogeneity in the Population 



305 



sight so soon ? The Tlalnepantla colony also shows the same definite response 

 in the population as a whole to the complex, and the Chapultepec and Puebla 

 colonies each shows its characteristic difference in the population at the loca- 

 tion. Thus each of the population masses varies in its location in differing 

 degrees in several directions, and all may well he present at one time, producing 

 a well-defined condition of " indefinite variation " in the population, which in 

 turn may be followed by decided " definite variation " in Darwin's sense as the 

 result of some minor change in the direction of incidence or intensity of some of 

 the factors in the medium, of which instances are fairly frequent in the data 

 presented. 



19C)4- 



I90S_ 



1906 



1907 



1908 



1909 



_iL 



.M. 



^m ^vr jv ^Y[ 



ivn gvm gix gx 



sxi 



am gun ^yiv 



Fig. 111. — Composite figure representing results observed at five colonies de- 

 scribed in preceding pages and change in the appearance of the population in suc- 

 cessive generations through a period of years. Corresponding determinations are 

 arranged one above the other, so that conditions prevailing in the population at a 

 given time in the colonies are comparable. This figure shows graphically the 

 behavior in the population which the different colonies presented and which are 

 apparently constant conditions in the habitats studied. 



The condition presented in a complex character of this kind, as a type of 

 what one might expect to find in more complicated forms or in organisms as a 

 whole were it possible to analyze the relations fully, is suggestive, and is one 

 that may well have played a role in the production of the heterogeneity that 

 exists in the organized world. Darwin certainly saw the conditions in nature 

 in this respect and tried to estimate them on the basis of their value in species 

 formation, on the basis of a working hypothesis that he was not able to put to an 

 exhaustive experimental test. With Darwin, as since, it has been entirely a 

 matter of opinion as to how conditions like these operated in nature to produce 

 heterogeneity and stable permanent groups under natural conditions. This is 

 still too much a matter of opinion and plausibilities, but should be a matter 



