OTHER THEORIES OF SPECIES-FORMING.. 265- 



immature life can effect very considerable changes in some 

 Theconcep- of its body-parts by special use or disuse of 



tion of evolution thege t Qr that certa j n parts may be modi- 

 accordmg to ... 



Lamarck, fied through the influence of external stimuli, is 



familiar knowledge. Let one recall the increase of the 

 blacksmith's biceps and inversely the degeneration of un- 

 used muscles, and the thickening or callousing of palms or 

 other parts of the skin exposed to repeated rough contact- 

 Bones have ridges developed on them by repeated muscle- 

 pulls, the hands and eyes can be trained to special functional 

 skill which involves important although perhaps slight physi- 

 cal changes, the heart and lungs can be enlarged by special 

 use ; in short, almost any of the organs of the body, which 

 are actively used, can be modified either by unusual or extra 

 use, or by unusual lack of use. Now this use is, in Nature, 

 almost always of the character of a better aiding in success- 

 ful living ; that is, it is adaptive use. Animals often chased 

 by enemies become fleeter by practice; animals that must 

 dig for roots or climb trees for leaves and fruits, or dive for 

 fishes, or leap over obstacles, come by repeated digging, climb- 

 ing, diving, or leaping to do these things better ; the muscles 

 and tendons and bones work together better and better,. 

 become physically modified in accordance with these endeav- 

 ours. If such betterment of organs and their functions 

 acquired by individuals could be inherited by their young, 

 it is obvious that general adaptations of this sort could be 

 rapidly developed in the course of generations, and new 

 species, new, that is, because of the adaptive changes thus 

 effected, be formed. This is the essential thought in 

 Lamarck's theory of the method of adaptation and species- 

 forming. In almost all criticisms of Lamarckism one reads 

 much contemptuous reference to the expected results of the 

 organism's "willing" to vary or change in this or that direc- 

 tion. As a matter of fact the critics of Lamarckism give 

 that rather absurd feature of alleged Lamarckism much 



