72 THE GENESIS OF SPECIES. [Chap. 



island will gradually acquire a Avliite, or even a yellow, pop- 

 ulation?" 



" Darwin says that in the struggle for life a grain may 

 turn the balance in favor of u given structure, which will tlien 

 be preserved. But one of the weiglits in the scale of Nature 

 is due to the number of a given tribe. Let there be 7,000 

 A's and 7,000 B's, representing two varieties of a given an- 

 imal, and let all the B's, in virtue of a slight diilcrence of 

 structure, have the better chance of life by y^Vo" part. We 

 must allow that tliere is a sligiit probability that the de- 

 scendants of B will supplant the descendants of A; but 

 let there be only 7,001 A's against 7,000 B's at first, and the 

 chances are once more equal, while if there be 7,002 A's to 

 start, the odds would be laid on the A's. True, they stand 

 a greater chance of being killed ; but then they can better 

 aflord to be killed. The grain will only turn the scales 

 when these are very nicely balanced, and an advantage in 

 numbers counts for weight, even as an advantage in struct- 

 ure. As the numbers of the favored variety diminish, so 

 must its relative advantages increase, if the chance of its 

 existence is to surpass the chance of its extinction, until 

 hardly any conceivable advantage would enable the de- 

 scendants of a single pair to exterminate the descendants 

 of many thousands if they and their descendants are su]> 

 posed to breed freely ^vith the inferior variety, and so grad- 

 ually lose their ascendency." 



Mr. Darwin himself says of the article quoted : " The 

 justice of these remarks cannot, I 'think, be disputed. If, 

 for instance, a bird of some kind could procure its food more 

 easily by having its beak curved, and if one were born Avith 

 its beak strongly cuived, and which consequently flourished, 

 nevertheless there would be a very poor chance of this one 

 individual perpetuating its kind to the exclusion of the com- 

 mon form." This admission seems almost to amount to a 

 change of front in the face of the enemy I 



