Chap. XIY. 
RECAPITULATION. 
469 
nature. But, besides such differences, all naturalists 
have admitted the existence of varieties, which they 
think sufficiently distinct to be worthy of record in sys¬ 
tematic works. No one can draw any clear distinction 
between individual differences and slight varieties; or 
between more plainly marked varieties and sub-species, 
and species. Let it be observed how naturalists differ 
in the rank which they assign to the many representative 
forms in Europe and North America. 
If then we have under nature variability and a power¬ 
ful agent always ready to act and select, why should we 
doubt that variations in any way useful to beings, under 
their excessively complex relations of life, would be pre¬ 
served, accumulated, and inherited ? Why, if man can 
by patience select variations most useful to himself, 
should nature fail in selecting variations useful, under 
changing conditions of life, to her living products? 
What limit can be put to this power, acting during long 
ages and rigidly scrutinising the whole constitution, 
structure, and habits of each creature,—favouring the 
good and rejecting the bad ? I can see no limit to this 
power, in slowly and beautifully adapting each form 
to the most complex relations of life. The theory of 
natural selection, even if we looked no further than this, 
seems to me to be in itself probable. I have already 
recapitulated, as fairly as I could, the opposed difficulties 
and objections: now let us turn to the special facts and 
arguments in favour of the theory. 
On the view that species are only strongly marked 
and permanent varieties, and that each species first 
existed as a variety, we can see why it is that no line 
of demarcation can be drawn between species, com¬ 
monly supposed to have been produced by special acts 
of creation, and varieties which are acknowledged to 
have been produced by secondary laws. On this same 
