no THEORIES OF EVOLUTION 



who are remarkable for any intellectual or structural 

 feature, their descendants, although some of them may 

 partake of their parents' peculiarities, sometimes even to 

 an increased extent, will ultimately return to the pattern 

 of the race. There is always a ' recession towards 

 mediocrity'. Hence, unguided variation can never 

 explain the ' origin of the fittest '. [Since these last words 

 were written De Vries and others have brought forward 

 many facts which, as they believe, support the hypothesis 

 that sudden large variations lead to a fresh position of 

 organic stability and the origin of a new species by 

 ' Mutation '. Natural Selection is, however, still invoked 

 in order to arbitrate between different mutations, as well 

 as between these and the parent species. A final decision 

 as to whether the course of evolutionary history has been 

 interrupted or continuous will probably be reached by the 

 study of Palaeontology.] 



I have briefly touched on some of the chief difficulties 

 which are advanced against Natural Selection. I now 

 propose to devote the remaining part of my time to the 

 difficulties which seem to me to apply to the Lamarckian 

 Theory. 



Lamarckian Evolution, as I have mentioned before, 

 depends upon acquired characters. A good deal of mis- 

 conception has arisen from this use of the word ' acquired'. 

 An acquired character has sometimes been interpreted to 

 mean any character that an animal has come to possess ; 

 hence, inherent and acquired characters have been con- 

 fused. The word ' acquired ', as used by biologists, must 

 be understood to have a limited and special application, 

 meaning only those characters which have been produced 

 in the organism by the incidence of external forces, or by 

 the action of its own forces, use and disuse of parts, and 

 so on, during its life. Weismann has suggested the term 

 ' Blastogenic ' for characters potentially present in the 

 germ at the very beginning of life, and 'Somatogenic' 

 for those which appear afterwards and are not potentially 

 present in the germ. Here blastogenic is the equivalent 

 of inherent, and somatogenic of acquired. 



Some years ago I suggested that the terms ' Centri- 



