Heredity and Natural Selection. 277 



thing to take its place. This has not prevented Darwin 

 himself from jierceiving the weight of the criticism, but 

 it has certainly caused the objections to be ignored or 

 overlooked by other less candid writers. 



Natural selection cannot act unless many individual 



vary together. 



One of the most serious objections to Darwin's theory is 

 based upon the fact that while natural selection requires 

 that great numbers of individuals shall vary iu essentially 

 the same way at nearly the same time, the chance against 

 this, if variations are fortuitous in Darwin's sense, is 

 great beyond all computation. 



In 1804 the writer of what Darwin terms "an able 

 and valuable article" in the North British Review, called 

 attention to the fact that, according to the law of 

 chances, slight variations, however useful, will tend 

 to bo obliterated, instead of perpetuated, by natural 

 selection, unless they simultaneously appear in a great 

 number of individuals. Unless we can show that 

 the causes of variability act in such a way as to affect 

 many individuals at the same time, and cause the 

 same part to vary in all of them, we must regard this as 

 a very serious objection to the theory of natural selec- 

 tion, and Darwin himself acknowledges {Origin of Spe- 

 cies, p. 72) that the justice of this objection cannot be 

 disputed. He admits in the later editions of the 

 Origin of Species, p. 71, that until reading the able and 

 valuable article in the North British Revieiu, he did not 

 appreciate how rarely single variations, whether slight 

 or strongly marked, would be perpetuated. 



The reviewer points out that it is difficult to see how 

 a species can be changed by the survival of the descend- 

 ants of a few individuals which possess some favorable 



