OTHER THEORIES OF SPECIES-FORMING. 263 



planation of adaptation and species-forming known as La- 

 marckism. Lamarck * proposed his theory at 



Lamarckism. J . . , , 



a time most inopportune ; it met with no gen- 

 eral acceptance, but in later years, post-Darwinian years, 

 fair-minded biologists have turned back to the books and 

 papers of this pioneer French exponent of the evolution 

 principle and have given his theory the careful attention and 

 scrutiny it deserves but which it failed to get from 

 Lamarck's contemporaries. This reexamination of the La- 

 marckian theory or theories has given rise to most radically 

 divergent opinion and belief concerning its worth : many 

 biologists account it of great value, others reject it prac- 

 tically in toio. But this acceptance or rejection depends 

 almost entirely on one's attitude toward a single funda- 

 mental part of it, namely, the assumption that variations, 

 modifications, or characteristics acquired during the life- 

 time of an individual, these modifications usually being due 

 to use, disuse, or other functional stimulation of organs and 

 parts, can be transmitted by this individual to its offspring. 

 If such newly-acquired, non-inherited characteristics can be 

 transmitted in full and in detail, or even approximately so, 

 from the parent to the young, then Lamarckism obviously 

 offers the simplest of all the explanations so far presented, 

 of nearly all active and of many passive adaptations. If 

 such characters cannot be so transmitted, then Lamarckism, 

 as plausible, as reasonable, as simple and effective as it 

 seems to be, is practically without validity. 



Now this matter of the inheritance of acquired charac- 

 ters, apparently easily susceptible of definite proof or refuta- 

 m , tion bv observation and experiment, has been 



The inheritance 



of acquired char- for years and is to-day one of the burning prob- 

 lems of biology. There is no general agree- 

 ment about it, no consensus of authority even. Just at pres- 

 ent the weight of evidence inclines strongly against such 

 an inheritance, chiefly because of Weismann's successfully 



