626 



SCIENCE. 



[N. S. Vol. IV. No. 96. 



— a difl&culty which is equally obvious and 

 of equal moment to the highly-trained in- 

 vestigator and the man who is keenly in- 

 terested in the results obtained by others, 

 but cannot himself lay claim to the posi- 

 tion and authority of a skilled observer; to 

 the naturalist, and to the one who follows 

 some other branch of knowledge but is in- 

 terested in the progress of a sister science. 



Two such difficulties were alluded to by 

 Lord Salisbury in his interesting presiden- 

 tial address to the British Association at 

 Oxford in 1894, when he spoke of ' two of 

 the strongest objections to the Darwinian 

 explanation ' of evolution — viz, the theory 

 of natural selection — as appearing ' still to 

 retain all their force.' The first of these 

 objections was the insufficiency of the time 

 during which the earth has been in a habit- 

 able state, as calculated by Lord Kelvin 

 and Prof. Tait, 100 million years being con- 

 ceded by the former, but only 10 million by 

 the latter. Lord Salisbury quite rightly 

 stated that for the evolution of the organic 

 world as we know it by the slow process of 

 natural selection at least many hundred 

 million years are required; whereas, " if the 

 mathematicians are right, the biologists 

 cannot have what they demand. ^ * >i^ The 

 jelly-fish would have been dissipated in 

 steam long before he had had a chance 

 of displaying the advantageous variation 

 which was to make him the ancestor of the 

 human race." 



The second objection was that " we can- 

 not demonstrate the process of natural 

 selection in detail; we cannot even, with 

 more or less ease, imagine it." "In natural 

 selection who is to supply the breeder's 

 place ?" " There would be nothing but mere 

 chance to secure that the advantageously 

 varied bridegroom at one end of the wood 

 should meet the bride, who by a happy con- 

 tingency had been advantageously varied 

 in the same direction at the same time at 

 the other end of the wood. It would be a 



mere chance if they ever knew of each 

 other's existence; a still more unlikely 

 chance that they should resist on both sides 

 all temptations to a less advantageous alli- 

 ance. But unless they did so the new breed 

 would never even begin, let alone the ques- 

 tion of its perpetuation after it had begun." 



Prof. Huxley, in seconding the vote of 

 thanks to the President, said that he could 

 imagine that certain parts of the address 

 might raise a very good discussion in one 

 of the Sections, and I have little doubt that 

 he referred to these criticisms and to this 

 Section. When I had to face the duty of 

 preparing this address I could find no sub- 

 jects better than those provided by Lord 

 Salisbury. 



At first the second objection seemed to 

 ofier the more attractive subject. It was 

 clear that the theory of natural selection as 

 held by Darwin was misconceived by the 

 speaker, and that the criticism was ill- 

 aimed. Darwin and Wallace, from the very 

 first, considered that the minute differences 

 which separate individuals were of far more 

 importance than the large single variations 

 which occasionally arise — Lord Salisbury's 

 advantageously varied bride and bride- 

 groom at opposite ends of the wood. In 

 fact, after Fleeming Jenkins' criticisms in 

 the North British Review for June 1867, Dar- 

 win abandoned these large single variations 

 altogether. Thus he wrote in a letter to 

 Wallace (February 2, 1869): "I always 

 thought individual difi"erences more impor- 

 tant ; but I was blind, and thought single 

 variations might be preserved much oftener 

 than I now see is possible or probable. I 

 mentioned this in my former note merely 

 because I believed that you had come to a 

 similar conclusion, and I like much to be 

 in accord with you."^ Hence we may infer 

 that the other great discoverer of natural 

 selection had come to the same conclusion 

 at an even earlier date. But this fact re- 



* Life and Letters^ Vol. III. 



