been offered of the structural similarities between species 

 within' the same group, is the hypothesis of a common de- 

 scent from a parent species. But he emphatically rejects 

 the notion — and this is the quintessence of Darwinism — 

 that the dissimilarities between species have been brought 

 about by the purely mechanical agency of natural selection. 



To find out what, precisely, Darwin meant by the 

 term "natural selection" let us turn for a moment, to his 

 great work. The Origin cf Species by Means of Natural Se- 

 lection. In the second chapter of that work, Darwin ob- 

 serves that small "fortuitous" variations in individual or- 

 ganisms, though of small interest to the systematist, are of 

 the "highest importance" for his theory, since these minute 

 variations often confer on the possessor of them, some ad- 

 vantage over his fellows in the quest for the necessaries of 

 life. Thus these chance individual variations become the 

 "first steps" towards sHght varieties, which, in turn, lead to 

 sub-species, and, finally, to species. Varieties, in fact, are 

 "incipient species." Hence, small "fortuitous" fluctuating, 

 individual variations — i. e., those which chance to occur 

 without predetermined direction — are the "first-steps" in 

 the origin of species. This is the first element in the Dar- 

 v/inian theory. 



In the third chapter of the same work we read : "It has 

 been seen in the last chapter that amongst organic beings 

 in a state of nature there is some individual variability. * * * 

 But the mere existence of individual variability and of 

 some few well-marked varieties, though necessary as a 

 foundation of the work, helps us but little in understanding 



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