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By THE GENEALOGY OF ANIMALS 115 
that the tendency to vary, in a given organism, may 
_ have nothing to do with the external conditions to 
which that individual organism is exposed, but 
may depend wholly upon internal conditions. No 
one, I imagine, would dream of seeking for the 
cause of the development of the sixth finger and 
toe in the famous Maltese, in the direct influence 
of the external conditions of his life. 
I conceive that both hereditary transmission 
and adaptation need to be analysed into their 
constituent conditions by the further application 
of the doctrine of the Struggle for Existence. It 
is a probable hypothesis, that what the world is to 
organisms in general, each organism is to the 
molecules of which it is composed. Multitudes of 
these, having diverse tendencies, are competing 
with one another for opportunity to exist and 
multiply ; and the organism, as a whole, is as 
much the product of the molecules which are 
victorious as the Fauna, or Flora, of a country is 
the product of the victorious organic beings in it. 
On this hypothesis, hereditary transmission is 
the result of the victory of particular molecules 
contained in the impregnated germ. Adaptation 
to conditions is the result of the favouring of the 
multiplication of those molecules whose organising 
tendencies are most in harmony with such 
conditions. In this view of the matter, conditions 
are not actively productive, but are passively 
permissive ; they do not cause variation in any 
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