“Factors of Organic Evolution” 107 
got plants and animals as embodiments of the two great 
fundamental principles on which it is alone possible that 
life can be conducted,* and species of plants and animals as 
embodiments of the details involved in carrying out these 
two main principles. 
If the earliest organism could have only varied favourably 
in one direction, the one possible favourable accidental 
variation would have accumulated so long as the organism 
continued to exist at all, inasmuch as this would be pre- 
served whenever it happened to occur, while every other 
would be lost in the struggle of competitive forms; but 
even in the lowest forms of life there is more than one 
condition in respect of which the organism must be supposed 
sensitive, and there are as many directions in which varia- 
tions may be favourable as there are conditions of the 
environment that affect the organism. We cannot con- 
ceive of a living form as having a power of adaptation 
limited to one direction only ; the elasticity which admits 
of a not being “‘ extreme to mark that which is done amiss ” 
in one direction will commonly admit of it in as many 
directions as there are possible favourable modes of varia- 
tion ; the number of these, as has been just said, depends 
upon the number of the conditions of the environment that 
affect the organism, and these last, though in the long run 
and over considerable intervals of time tolerably constant, 
are over shorter intervals liable to frequent and great 
changes ; so that there is nothing in Mr. Charles Darwin’s 
system of modification through the natural survival of the 
lucky, to prevent gain in one direction one year from being 
lost irretrievably in the next, through the greater success 
of some in no way correlated variation, the fortunate 
possessors of which alone survive. This, in its turn, is as 
likely as not to disappear shortly through the arising of 
some difficulty in some entirely new direction, and so on ; 
nor, if function be regarded as of small effect in determining 
* See concluding chapter. 
