THEORIES OF LAMARCK AND DARWIN 383 



arise in animals niainly through use and disuse, and new 

 organs have their origin in a physiological need. A new need 

 feltby the animal impressesitself on the organism, stimulating 

 growth and adaptations in a particular direction. This part 

 of Lamarck's theory has been subjected to much ridicule. 

 The sense in which he employs the word hesoin has been 

 much misunderstood; when, however, we take into ac- 

 count that he uses it, not merely as expressing a wish or 

 desire on the part of the animal, but as the reflex action 

 arising from new conditions, his statement loses its alleged 

 grotesqueness and seems to be founded on sound physiology. 



Inheritance. — Lamarck's view of heredity was uncritical; 

 according to his conception, inheritance was a simple, direct 

 transmission of those superficial changes that arise in organs 

 within the lifetime of an individual owing to use and disuse. 

 It is on this question of the direct inheritance of variations 

 acquired in the lifetime of an individual that his theory has 

 been the most assailed. The belief in the inheritance of 

 acquired characteristics has been so undermined by experi- 

 mental evidence that at the present time we can not point 

 to a single unchallenged instance of such inheritance. But, 

 while Lamarck's theory has shown weakness on that side, 

 his ideas regarding the production of variations have been 

 revived and extended. 



Variation. — The more commendable part of his theory 

 is the attempt to account for variation. Darwin assumed 

 variation, but Lamarck attempted to account for it, and in 

 this feature many discerning students maintain that the 

 theory of Lamarck is more philosophical in its foundation 

 than that of Darwin. 



In any theory of evolution we must deal with the variation 

 of organisms and heredity, and thus we observe that the two 

 factors discussed by Lamarck are basal. Although it must 

 be admitted that even to-day we know little about either 



