THE UNDERLYING IDEA 4S 
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 
and, 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 
