Nature of Variation 
in the expressions he used concerning it, he 
assumed that variations are indefinite in variety 
and occur indiscriminately in all directions, as 
the following quotations from the Origin of 
Species will show: “ But the number and diver- 
sity of inheritable deviations of structure . . 
are endless” (page 14, ed. 1902). ‘‘ The varia- 
tions are supposed to be extremely slight, but of 
the most diversified nature.” ‘I have hitherto 
sometimes spoken as if the variations so common 
and multiform with organic beings under domes- 
tication, and in a lesser degree to those under 
nature, were due to chance. This, of course, is 
a wholly incorrect expression, but it serves to 
acknowledge plainly our ignorance of the cause 
of each particular variation ” (page 164). 
Wallace is far less guarded in his expressions. 
On page 82 of his Darwznzsm he speaks of “the 
constant and large amount of variation of every 
part in all directions . . . which must afford an 
ample supply of favourable variations whenever 
required.” 
The double assumption that variations are for 
all practical purposes haphazard in origin and 
indefinite in direction is necessary if natural 
selection is to be the main factor in evolution. 
For if variations be not haphazard, if they are 
definite, if there be a directive force behind them, 
like fate behind the classical gods, then selection 
is not the fundamental cause of evolution. It 
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