m 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 (b) 

 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 (5), 

 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 lie at the foundation of all Mr. Darwin's 

 reasoning ; that he should confound an irrefragable 



