DESCENT WITH CHANGE 373 



appreciate the overwhelming impressiveness of all the concordant 

 evidence for organic evolution. 



B. Factors of Organic Evolution 



Taking for granted the fact of evolution, what are the factors 

 which have brought about evolution? That is quite a different 

 question, but one which has often brought confusion to the popular 

 mind. Although biologists are in general agreement on the basic 

 factors involved, there is much debate in regard to their relative 

 importance and method of operation. And the layman has mis- 

 taken the questioning of one factor or another for a questioning 

 of the fact. 



No purpose will be served by a long historical account of the 

 origin of the present-day point of view. Suffice it to say that the 

 evolution idea is a generalization which has crept from science to 

 science — from astronomy to geology, from geology to biology, 

 thereupon becoming organic evolution. The idea in one form or 

 another is as old as history, but for all practical purposes the biol- 

 ogist Lamarck, during the early part of the nineteenth century, 

 formulated the first consistently worked out theory of organic 

 evolution. (Fig. 293.) 



1. Lamarckism 



The evidence for organic evolution offered by Lamarck was 

 necessarily limited in amount, and in some cases neither happily 

 selected nor convincingly presented, so it was laughed out of court 

 by biologists and laymen alike. His evolution factor was essentially 

 the change of the organism through the use and disuse of parts; 

 the physiological response of the organism to new needs offered by 

 new conditions of life. And these changes, somatic in origin, he 

 believed were transmitted to the progeny. His first statement in 

 1809, freely translated, is as follows: 



'First Law: In every animal which has not exceeded the term 

 of its development, the more frequent and sustained use of any 

 organ gradually strengthens this organ, develops, and enlarges it, 

 and gives it a strength proportioned to the length of time of such 

 use, while the constant lack of use of such an organ imperceptibly 

 weakens it, causing it to become reduced, progressively diminishes 

 its faculties, and ends in its disappearance. 



"Second Law: Everything which nature has caused individuals 



