140 THE DOCTRINE OF DESCENT. 
that doubtful species are not exceptional, as the old 
school was wont to imagine, but that it is merely owing 
to an inadequate knowledge of the material out of which 
species are constructed, that all species are not looked 
upon as doubtful and artificial. 
Let us here again call to mind that in many thou- 
sand cases the most rigid systematizers are unable 
to state where their species begin and end; of which 
Darwin, as an instance, cites a communication by 
H. C. Watson, that 182 British plants, usually regarded 
as varieties, have each been claimed as independent 
species by individual botanists.** Darwin’s immortal 
service consists in having shown what is the power 
which operates upon the existing variable individuals 
and species, and what results this operation must pro- 
duce. He found the key in the word which has become 
a badge and common property of our age, “the struggle 
for life,’* and has thus given the foundation and theory 
of a doctrine of which the truth had long before been 
taanifest to an intellect such as that of Lamarck. He 
founded the doctrine of Descent on the theory of selec- 
tion, when he proved that in nature the struggle for 
existence occasions a selection of the best and fittest, 
comparable to artificial breeding, and giving rise to new 
races and new species. 
“The struggle for life, this Jdellum omnium contra 
ouines, is, moreover, an undisputed and undeniable fact, 
which we here accept in its widest relations. Not only 
does the beast of prey war against the graminivorous 
animals, which again strive to keep their balance by 
superior multiplication, speed, and cunning; the gradual 
* For Wallace's share in this honour, ste the end of this chapter, 
