CHAPTER VII 



THE INHERITANCE OF ACQUIRED CHARACTERS AS 

 A FACTOR IN EVOLUTION 



Lamarck's Theory 



One of the most striking and peculiar characteristics of 

 living things is that through use a part is able to carry out 

 a particular function better than before, and in some cases 

 the use of the part leads to its increase in size. Conversely, 

 disuse leads to the decrease of a part in size. We are per- 

 fectly familiar with this process in ourselves as applied to our 

 nervous system and muscles. 



It is not surprising that the idea should have arisen that, 

 if the results of the use of a part are inherited by the next 

 generation, the adaptation of organisms might be explained 

 in this way. The presence of the organs of touch, in those 

 parts of the body that are more likely to come into contact 

 with foreign bodies, offers a striking parallel to the perfecting 

 of the sensation of touch that can be brought about through 

 the use of any part. The development of eyes only on the 

 exposed parts of the body, as on the tentacles of the seden- 

 tary annelids, or along the margin of the mantle of a bivalve 

 mollusk, suggests that there may be some direct connection 

 between their presence in these regions and the effect of 

 light on the parts. In fact, ever since the time of Lamarck, 

 there have been many zoologists who have claimed that many 

 of the adaptations of organisms have arisen in this way, that 

 is, through the inheritance of the characters acquired through 

 use. In general this theory is summed up in the phrase, 

 "the inheritance of acquired characters." 



