WHAT WE OWE TO DARWIN 15 



Darwin recognised the occurrence of structural 

 changes directly due to changed surroundings 

 and changed habits, which he called " definite 

 variations," which are now usually called modi- 

 fications, or "acquired characters"; and he believed 

 that these were, in some cases, transmitted. This 

 is the characteristic Lamarckian position. But the 

 raw materials of progress which Darwin chiefly 

 relied on were what he called the " numerous, suc- 

 cessive, shght, favourable variations " (" Origin of 

 Species," p. 421). He also took account of " sudden 

 and considerable deviations of structure " — " single 

 or occasional variations," as he called them ; but 

 he very deliberately refrained from attaching 

 importance to such leaps and bounds, thinking 

 that they had no staying power in inheritance. 

 As to the causes of the inborn variations in Hving 

 creatures, Darwin had no Kght, and, with his 

 characteristic candour, said so. 



(IV) Natural Selection. — What do we owe 

 to Darwin ? The theory of Natural Selection, 

 which his magnanimous fellow-worker, Alfred 

 Russel Wallace, independently stated at the same 

 time (1858), and of which there had been a few 

 previous suggestions of a more or less vague de- 

 scription. It was here that Darwin's originahty 

 was greatest, for he revealed the many different 

 forms — often very subtle — which Natural Selection 

 takes, and, with the insight of a disciplined scientific 

 imagination, he realised what a mighty engine of 

 progress it has been and is. His theory is simple 

 and admits of brief statement. We can under- 

 stand Huxley's remark : " How extremely stupid 

 not to have thought of that ! " 



(1) Variabihty is a fact of life. The members of 



