CHAPTER VL 
PURE DARWINISM (continued). 
(b) MORE METHODS OF SELECTION THAN ONE. 
“Ilya fagots et fagots.”—Moliere. 
There are, to say the least, three conceivable ways in 
which similar variations may be isolated for breeding pur 
poses in the world of nature, apart from Natural Selection. 
Physical separation, which is so effectual in artificial selec 
tion, might also operate in nature. Similar variants might 
segregate themselves with results similar to those of arti 
ficial selection ; similar variants might be physiologically 
differentiated so that either their period of sexual maturity 
differed from that of the rest of the race, or they might 
be fertile inter se and infertile with the rest of the race. 
And I see no reason whatever why these three principles 
should not prove as efficient in nature as the principle of 
Natural Selection is supposed to be, on the hypothesis that 
the tacit assumptions of that theory are to be relied on. 
Let us consider, for a moment, what these assumptions are. 
Those who believe that Natural Selection is the sole cause 
of the transmutation of species, argue on the ground of 
the necessity of “ selecting ”—that is, of isolating for breed 
ing purposes—those similar favourable variations which 
arise in connection with variations necessarily associated 
with sexual reproduction. They assert that the agent of