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a CRITICISMS ON “ THE ORIGIN OF SPECIES” 101 
than M. Flourens; but they are logical deductions 
from the assertion just quoted, and from the 
further statement that natural selection means 
only that “organisation chooses and _ selects 
organisation.” 
For if it be once admitted (what no sane man 
_ denies) that the chances of life of any given 
organism are increased by certain conditions (A) 
and diminished by their opposites (B), then it is 
mathematically certain that any change of con- 
ditions in the direction of (A) will exercise a 
selective influence in favour of that organism, 
tending to its increase and multiplication, while 
any change in the direction of (B) will exercise a 
selective influence against that organism, tending 
to its decrease and extinction. 
Or, on the other hand, conditions remaining the 
same, let a given organism vary (and no one 
doubts that they do vary) in two directions: into 
one form (a) better fitted to cope with these con- 
ditions than the original stock, and a second (d) 
less well adapted to them, Then it is no less certain 
that the conditions in question must exercise a 
selective influence in favour of (a) and against (6), 
so that (a) will tend to predominance, and ()) to 
extirpation. 
That M. Flourens should be unable to perceive 
the logical necessity of these simple arguments, 
which le at the foundation of all Mr. Darwin’s 
reasoning ; that he should confound an irrefragable 
