Influence of Selection 199 
considered. It is a vital question for the theory of’ evolution 
whether 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 accomplish 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: 
inclined 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 
1 This example is taken from Davenport’s paper, Popular Science Monthly, 
1902. 
