Variation and Heredity 299 
will be kept from crossing with the parent form, and since this 
new character will be present from the beginning, the new form 
will have much better chances of surviving than if a difference 
in time of reaching maturity had to be gradually acquired. 
4. The new species that appear may be in some cases 
already adapted to live, in a different environment from that 
occupied by the parent form; and if so, it will be isolated 
from the beginning, which will be an advantage in avoiding 
the bad effects of intercrossing. 
5. It is well known that the differences between related 
species consists largely in differences of unimportant organs, 
and this is in harmony with the mutation theory, but one of 
the real difficulties of the selection theory. 
6. Useless or even slightly injurious characters may appear 
as mutations, and if they do not seriously affect the perpetua- 
tion of the race, they may persist. 
In Chapters X and XI, an attempt will be made to point 
out in detail the advantages which the mutation theory has 
over the Darwinian theory. 
