CHAPTER XIX 



THE INFLUENCE OF HABITS AND SURROUNDINGS 



i. The Influence .of Function 2. The Influence of Surroundings 



3. Our own Environment 



i. The Influence of Function. A skilled observer can 

 often discern a man's occupation from his physiognomy, 

 his shoulders, or his hands. In some unhealthy occupa- 

 tions the death-rate is three times that in others. Disuse 

 of such organs as muscles tends to their degeneration, for 

 the nerves which control them lose their tone and the 

 circulation of blood is affected ; while on the other hand 

 increased exercise is within certain limits associated with 

 increased development. A force de forger on devient 

 forgeron. 



If we knew more about animals we might be able to cite 

 many cases in which change of function produced change of 

 structure, but there are few careful observations bearing on 

 this question. 



Even if we could gather many illustrations of the 

 influence of use and disuse on individual animals, we should 

 still have to find out whether the precise characters thus 

 acquired by individuals were transmissible to the offspring, 

 or whether any secondary effects of the acquired characters 

 were transmissible, or whether these changes had no effect 

 upon succeeding generations. As there are few facts to argue 

 from, the answers given to these questions are not reliable. 



It is easy to find hundreds of cases in which the constant 



