Influence of Selection 199 



considered. It is a vital question for the theory of evolution 

 w^hether new forms, new species, can be created by the selection of 

 fluctuating or individual variations as the Darwinian school has 

 claimed for nearly fifty years. Experiment alone can decide 

 whether this claim is justified. That new forms have appeared 

 as a result of selection by man no one will deny ; for most of 

 our domesticated animals and cultivated plants bear direct testi- 

 mony in favor of this view; but the cardinal question remains 

 whether elementary varieties and species, or fluctuating varia- 

 tions, have been intentionally or unintentionally picked out in 

 the formation of new races. 



Fluctuating or Individual Differences 



Whatever systematic definition of species may prove most 

 satisfactory, the fact that no two individuals are alike is what 

 concerns us at present. I shall first give an account of the law 

 followed by these fluctuations, then an account of their inheri- 

 tance, and finally consider what man can accompHsh by their 

 selection and breeding. 



Quetelet first drew attention to the law followed by fluctuating 

 variations, and this law is spoken of as Quetelet's law. The 

 fluctuations of animals and plants appear as though they were 

 the outcome of chance, or, expressed differently, "the deviations 

 from the average obey the law of probability." Let us take 

 an example.^ If we examine a group of men as to their height, 

 we find by arranging them in a row that an almost continuous 

 straight line will connect the tops of their heads. The line 

 slopes from the tallest to the shortest man, but the slope is less 

 incHned in the middle than at the ends. This means that there 

 are in the middle region more men that are nearly the same 

 height. In another way this important fact can be brought out 

 more clearly. If we place in one column all the men between 

 64 and 65.9 inches; in another column to one side of the last all 

 the taller men between 66 and 67.9 inches; in another column 



^ This example is taken from Davenport's paper, Popular Science Monthly, 

 1902. 



