178 SCIENCE PROGRESS 



inheritance must be a vera causa. Nor does it seem impossible 

 that memory should rule the plasmic link which connects suc- 

 cessive generations — the true miracle of the camel passing 

 through the eye of a needle — since, as I have tried to show, the 

 reactions of living things to their surroundings exhibit in the 

 plainest way the universal presence of a mnemonic factor. 



We may fix our eyes on phylogeny and regard the living 

 world as a great chain of forms, each of which has learned some- 

 thing of which its predecessors were ignorant ; or we may attend 

 rather to ontogeny, where the lessons learned become in part 

 automatic. But we must remember that the distinction between 

 phylogeny and ontogeny is an artificial one, and that routine and 

 acquisition are blended in life. 



This is at any rate a plain challenge to Weissmann, and 

 what follows is an equally plain defence of natural selection. 



The great engine of natural selection is taunted nowadays, as 

 it was fifty years ago, with being merely a negative power. I 

 venture to think that the mnemonic hypothesis of evolution makes 

 a positive value of natural selection more obvious. If evolution 

 is a process of drilling organisms into habits, the elimination of 

 those that cannot learn is an integral part of the process, and is 

 no less real because it is carried out by a self-acting system. It 

 is surely a positive gain to the harmony of the universe that the 

 discordant strings should break. 



*&' 



As I listened to the slow and unemotional delivery of this 

 interesting and unorthodox address, it occurred to me how 

 differently it would have impressed the audience if they could 

 have been reminded of a delightful passage in Charles Darwin's 

 autobiography, edited by the speaker. The simplicity of it 

 makes it one of the great documents of the world, and this said 

 address appears in the light of it as an incomparably Darwinian 

 product. The passage is this : 



In 1880 I published, with Frank's assistance, our Power of 

 Movement in Plants. This was a tough bit of work. The 

 book bears much the same relation to my little book on 

 climbing plants which Cross Fertilisation did to the Fertilisation 

 of Orchids ; for in accordance with the principle of evolution 

 it was impossible to account for climbing plants having been 

 developed in so many widely different groups unless all kinds 

 of plants possess some power of movement of an analogous kind. 

 This I proved to be the case ; and I was further led to a rather 

 wide generalisation — namely, that the great and important classes 

 of movements, excited by light, the attraction of gravity, etc., are 

 all modified forms of the fundamental movement of circumnuta- 



