THE UNDERLYING IDEA 45 



be unsuspected. But once discovered and expounded, 

 thereafter anyone may follow out its workings. So 

 it is with the Darwinian idea of selection. It waited 

 long for a discoverer, but, once found, we cannot 

 but wonder why men did not see it earlier, it is so 

 simple. 



Mr. Darwin's mind, while slow and cautious, had 

 a wonderful perseverance. When he had finished his 

 work he had not only given a clear account of the 

 process of evolution, but he had foreseen almost all the 

 valid objections that were afterward to be brought 

 against his theory. Some of them he had explained 

 quite fully; of others he indicated a possible explana- 

 tion; of still other questions he confessed that as yet 

 they were not plain. But the whole theory is so 

 simple in its fundamental ideas that it has completely 

 revolutionized the whole aspect of modern biology 

 an'd, indeed, of modern thinking in many lines. 



There are four underlying conceptions, each simple 

 in itself, which must be clearly perceived before one 

 can understand Mr. Darwin's theory of "Natural 

 Selection." The first of these is known under the 

 name of Heredity. It is a matter of common ob- 

 servation that every animal or plant produces offspring 

 after its own kind. Under no conditions would we 

 expect a duck to lay an egg from which could hatch 

 anything but a duck. No Plymouth Rock chicken 



