CHAPTER IV 
DARWIN’S THEORIES OF ARTIFICIAL AND OF NATURAL 
SELECTION 
THE PRINCIPLE OF SELECTION 
Darwin’s theory of natural selection is preéminently a theory 
of adaptation. It appears, in fact, better suited to explain 
this phenomenon than that of the “origin of species.” Dar- 
win prepared his reader for the ideas contained in the theory 
of natural selection by a brief consideration of the results of 
artificial selection; and since the key to the situation is, I 
believe, to be found in just this supposed resemblance, we 
cannot do better than examine the theories in the order fol- 
lowed by Darwin himself. 
One of the means by which the artificial races of animals 
and plants have been formed by man is selection. The 
breeder picks out individuals having a certain peculiarity, and 
allows them to breed together. He hopes to find among 
the offspring, not only individuals like the parent forms, but 
also some that have the special peculiarity even more strongly 
developed. If such are found, they are isolated and allowed 
to breed, and in the next generation it is hoped to find one or 
more new individuals that show still more developed the 
special character that is sought. This process, repeated 
through a number of generations, is supposed to have led to 
the formation of many of our various forms of domesticated 
animals and plants. 
This heaping up as a result of the union of similar individ- 
uals cannot for a moment be supposed to be the outcome of 
the addition of the two variations to each other. Such an 
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