70 THE GENESIS OF SPECIES. [CHAP. 



cle he did not " appreciate how rarely single variations, 

 whether slight or strongly marked, could be perpetuated." 



The North British Review (speaking of the supposition 

 that a species is changed by the survival of a few individu- 

 als in a century through a similar and favorable variation) 

 says : " It is very difficult to see how this can be accom- 

 plished, even when the variation is eminently favorable in- 

 deed ; and still more difficult when the advantage gained is 

 very slight, as must generally be the case. The advantage, 

 whatever it may be, is utterly out-balanced by numerical 

 inferiority. A million creatures are born' ten thousand 

 survive to produce offspring. One of the million has twice 

 as good a -chance as any other of surviving ; but the chances 

 are fifty to one against the gifted individuals being one of 

 the hundred survivors. No doubt the chances are twice as 

 great against any one other individual, but this does not 

 prevent their being enormously in favor of some average in- 

 dividual. However slight the advantage may be, if it is 

 shared by half the individuals produced, it will probably be 

 present in at least fifty-one of the survivors, and in a larger 

 proportion of their offspring ; but the chances are against 

 the preservation oi any one ' sport ' (i. e., sudden, marked 

 variation) in a numerous tribe. The vague use of an im- 

 perfectly-understood doctrine of chance has led Darwinian 

 supporters, first, to confuse the two cases above distin- 

 guished ; and, secondly, to imagine that a very slight bal- 

 ance in favor of some individual sport must lead to its per- 

 petuation. All that can be said is that in the above ex- 

 ample the favored sport would be preserved once in fifty 

 times. Let us consider what will be its influence on the 

 main stock when preserved. It will breed and have a pro- 

 geny of say 100 ; now this progeny will, on the whole, be 

 intermediate between the average individual and the sport. 

 The odds in favor of one of this generation of the new breed 

 will be, say one and a half to one, as compared with the 



