EVIDENCES OF ORGANIC EVOLUTION 35 
have no reason whatever for supposing that domesti- 
cated species are more mutable than wild species, and 
there is consequently every reason to believe that 
changes of a similar character take place in Nature. 
Mr. Alfred Russell Wallace has quoted with approval 
Sir W. Thistelton Dyer’s criticism that if there is an 
equal chance of the occurrence or origin of new forms 
in nature and under cultivation, then their appearance 
—t.e., their survival until a stage at which they can 
be readily recognized as distinct from the original type 
—should be more frequent in nature than in cultiva- 
tion, because the former has a larger population to 
work with. The reply to this argument is obvious. 
In the first place, the much greater facilities for obser- 
vation under cultivation may fairly be set against the 
greater numbers stated to exist in nature ; but, in the 
second place, Mr. Wallace may well be challenged to 
cite a natural species of which a larger number of 
individuals has passed under man’s observation than 
is the case with cultivated wheat, for example. Buta 
third line of argument is much more conclusive than 
either of these. The modifications which occur under 
cultivation are in most cases decidedly weakly as com- 
pared with the original forms, as every gardener knows 
to his cost. They are only enabled to survive to a 
recognizable stage, because cultivation consists in the 
removal of competition ; all are given an equal chance. 
This is not soin nature. There, competition (according 
to the exponents of the Wallacian doctrine) is so intense 
that even very slight variations may determine success 
or failure. According to the doctrine of natural selec- 
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