CHAPTER IV 



THE LAMABCKIAN HYPOTHESIS OF THE INHERITANCE OP 

 ACQUIREB CHARACTERS 



The theory of evolution as expounded by Weismann stands in 

 direct contradiction to the older theory which has been in the 

 field since the days of its originator, Lamarck. The service 

 rendered by Lamarck to biological science by his proclamation 

 of the fundamental truth that the world of organisms as we 

 know it is not the result of a number of specific creations, but 

 of a long and complicated process of evolution from the simple 

 to the complex, from the homogeneous to the heterogeneous, 

 was a great and lasting service. The same cannot be said of his 

 explanation of the mechanism of the evolutionary process by 

 the hereditary transmission of bodily and mental modifications 

 resulting from functional use or disuse ; though this view has 

 until lately held a foremost place among the theories advanced 

 to explain the process of evolution. The LamarcMan theory is 

 founded entirely on the assumption that somatic characters, 

 whether physiological or psychological, are capable of being 

 modified by functional use or disuse or by surrounding condi- 

 tions, and that the modifications are capable of hereditary trans- 

 mission. A modification of an organ A, brought about by use 

 or disuse of this organ, is transmissible by heredity, and thus 

 the modification is definitely acquired for the race. The chief 

 origin of organic changes, according to Lamarck, is to be found 

 in the functional use or disuse of organs or parts of organs, and 

 the hereditary transmission of the modifications thus acquired. 



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