50 THE MEANING OF EVOLUTION 
Still others will be differently colored. They might be 
arranged to show a considerable gradation between 
the lightest and the darkest of the group, though 
there may not be anywhere in the row a considerable 
gap. It is variation in animals of the same parentage 
and same surroundings which in the mind of Mr. 
Darwin made evolution possible. He always favored 
the idea that it was the continuous accumulation of 
these small variations that finally produced the pro- 
found changes which mark the new species. He ad- 
mitted the possibility of the occasional appearance of 
“those more distinct leaps in variation on which the 
present school of mutationists so strongly insists; but 
_ he believed them to be less influential, in the general 
trend of evolution, than the slower but much more fre- 
quent variations. 
One of the most complicated and perplexing prob- 
lems in the biology of to-day is the question of the 
origin of these variations. It is quite as hard to 
understand as is the method by which animals pro- 
duce their own kind. No problem is being more 
earnestly studied. Suppositions we have in consider- 
able number, and two of these at least may reasonably 
be mentioned. We will consider first the less certain 
theory. There is nothing in the egg that in the re- 
motest degree resembles its parent. The old idea that 
every acorn had in it a miniature oak which only 
