7 8 THE POPULAR SCIENCE MONTHLY. 



phrase into the error of arguing in a circle ; for, in the case of not 

 a few creatures which have survived, it is difficult to give any 

 good reason for their survival except upon the assumption of 

 their fitness as proved by the very fact of their survival. Thus 

 their fitness leads to their survival, and this survival leads to the 

 conclusion that they must have been the fittest. Which is argu- 

 ing in a circle. Still further, it is not difficult to suggest exam- 

 ples in which the expression, survival of the fittest, manifestly 

 breaks down. Sir Isaac Newton was, as is well known, a very 

 delicate child, difficult to rear. Suppose that Newton and a pow- 

 erful navvy, or coal porter, or grenadier, had been compelled to 

 rough it as children at Dotheboys Hall or some similar establish- 

 ment, which would have survived ? Not Newton ; and yet it may 

 be fairly argued that in many respects he would have been the 

 fittest. Nor is this imaginary case an altogether unfair test of the 

 propriety of the phrase ; for it is impossible to give any true defi- 

 nition of fitness which shall exclude all moral and intellectual 

 qualities, all qualities in fact which are of the highest value, and 

 which shall simply include those elements of toughness and wiri- 

 ness, and strength of sinew or stomach, which are chiefly calcu- 

 lated to prolong life in trying circumstances. 



Putting out of consideration, however, the propriety of the 

 language by which survival in the struggle for life, whether 

 among vegetables or animals, is expressed, it is to be admitted 

 that the principle indicated is a true one. That is to say, it may 

 be regarded as admitted by all persons whose studies and natural 

 powers render their opinion of any real value, that modification 

 by natural selection is an element in that evolution of living 

 forms of which the evidence appears to be irresistible. Natural 

 selection is a vera causa ; the question is, What is the extent of 

 its action ? how much can it do ? 



Darwin considered it necessary to supplement natural by that 

 which he termed sexual selection ; in doing which he was quite 

 consistent, because he speaks (as we have already seen) of natural 

 selection as " the most important, but not the exclusive, means of 

 modification " of species. This supplemental hypothesis, however, 

 does not commend itself to Mr. Wallace's judgment. 



Mr. Darwin (he writes), as is well known, imputed most of the colors and 

 varied paterns of butterflies' wings to sexual selection — that is, to a constant 

 preference, by female butterflies, for the more brilliant males ; the colors thus 

 produced being sometimes transmitted to the males alone, sometimes to both 

 sexes. This view has always seemed to me unsupported by evidence, while it is 

 also quite inadequate to account for the facts. 



Again, after explaining his own views on the subject of orna- 

 mental appendages of birds and other animals, he writes : 



The various. facts and arguments now briefly set forth afford an explanation 



