260 CAUSES OF DEGENERATIVE EVOLUTION 



of only secondary importance in the development of 

 animals and plants, is a dominating element in 

 sociology. Institutions are able to modify their 

 structure by assimilating new inventions and im- 

 provements, and by getting rid of the useless parts. 

 On the other hand, indirect adaptation spread over 

 a species plays no part whatever in sociology, for 

 societies seldom reproduce the structures of the 

 societies from which they sprang, when the latter 

 have ceased to exist ; whereas, in animals, when a 

 useless organ is reproduced by hereditary repetition, 

 variability and natural selection become agents in 

 its suppression. 



CHAPTER I 



ATROPHY OF ORGANS 



PART II 



Causes producing atrophy 



THE ultimate cause of the atrophy of organs is the 

 limitation in the quantity of nourishment. We 

 have shown that if there were an indefinite supply 

 of food there would be no struggle, and, as a result, 

 no degeneration. We have now to examine more 

 minutely the course of atrophy and the nature of 

 its immediate causes. 



The atrophy of an organ is a reduction in 



