Analysis of Heterogeneity in the Population 323 



The methods here employed, with the information of the constitution of the 

 character and the experimental analysis of it have given the opportunity to 

 understand rather well the meaning of the conditions in the natural populations 

 that the censuses have revealed, and this is of value in the analysis of some of 

 the problems of the production and origin of species and minor groups in nature 

 and in experiment. 



I have been especially interested in the constant presence in the population of 

 " definite variation," which is true not only in the single population, but in each 

 location there is an unmistakable place response in which the population 

 " varied " in the same direction as the result of the conditions generally present 

 in the population and in the medium. I do not recall at present anyone who 

 has attempted continuous analyses of these responses in any population in 

 nature; rather most of the instances that are in the literature are the plausi- 

 bilities of records from few specimens or from determinations made at one time. 

 Nor do I recall that the use and recognition of the principle that Darwin so 

 clearly saw and believed might be of so much importance in the evolution of 

 organisms has been often mentioned or considered. There is an abundance of 

 argument concerning the production of the " directed " conditions which are 

 supposed to exist by " selection," but almost no attempts at the analysis of the 

 situation. Some few, as in the crab Carcinus, investigated by Weldon, gave 

 information that is at once suggestive and at the same time too incomplete to be 

 of much service in the analysis of the problem, and the results can be interpreted 

 on any basis one wishes. The incomplete facts as determined show only that 

 changes of some sort were in progress, either permanent in character or tem- 

 porary, ontogenetic or germinal, due to selection, environment, or any other 

 cause one wishes to introduce. The unquestioned fact of change existed, but 

 was not analyzed. 



There is no question but that the conditions as presented in the populations 

 represented here show this definite place " variation " in the population as a 

 whole in this complex character, and the census methods employed leave no 

 doubt of the reality of the conditions revealed. If these responses in the popu- 

 lation of a place as a whole to the conditions of the habitat have any meaning 

 with respect to the production of heterogeneity in nature, this set of materials 

 provides at least one opportunity to test it out. The populations as found in 

 the determinations and the general place tendencies in the population may be 

 produced by one of two general conditions ; either the place response may be due 

 to a real germinal difference in the race, or it may be due to the ever-present 

 action of the conditions, influencing the soma in a definite direction in its 

 " fluctuating variations," or it may be due to the presence in the location of 

 influences that eliminate a proportion of the population possessing certain char- 

 acters, so that the maturing population presents only the aspects of the portion 

 thereof that was able to escape the eliminating agents. A further possibility 

 is that the conditions seen in the population are the product of the combined 

 interaction of the character of the combining materials and the conditions of 

 the medium in the habitat. 



If the condition in the population at any location is a permanent one, then 

 the difi'erences that are presented may well be the basis of further differentia- 

 tion and in the end result in the production of a distinct localized race and 



