182 HABIT AND INTELLIGENCE. [chap. 



This is not assign any sucli merely physical reason for the fact that 

 physically ^^^ European race of man is unable to perpetuate itself in 

 explicable, the climate of Bengal. I believe such facts are to be 

 referred to the laws of habit. We have seen that every 

 organism has a certain power of becoming habituated to 

 impressions. This it does in two different ways : if the 

 impression demands a response, such as to close on its 

 prey or to run away from its enemy, the organism acquires 

 the habit of making the right response ; if it does not 

 demand nor admit of any response, the organism acquires 

 the habit of disregarding it. Now, exposure to a different 

 climate from that to which an organism has been accus- 

 tomed, in some cases, no doubt, produces a response in the 

 vegetative life — as, for instance, in those animals which 

 acquire a coat of hair better suited to their new abode ; 

 and sometimes it produces a response in the motor life, as 

 when it determines a species to acquire the liabit of peri- 

 odical migration. But in many cases — probably in the vast 

 majority — no appropriate response is possible. To use 

 familiar language, nothing can be done, and the change — 

 the unaccustomed heat or cold^must be endured. The 

 organism must become habituated to the climate — that is 

 to say, must acquire the habit of disregarding the change ; 

 Organisms and if it Cannot do this, the change will destroy its health, 

 stroved ^"^^ ultimately its life. It may not be sufficient to kill the 

 by changes individual ; but if its health is at all injured, and this is 

 cannot ^^ not recovered in future generations, the race will die out of 

 become its new abode. This kind of adaptability is very different 

 ated to. in different species : thus the horse has been successfully 

 introduced by man into every climate, from the equator 

 to Iceland and Siberia : the ass would perish in a very 

 cold climate. 



The reasoning in the foregoing paragraph may seem 

 Great and "^^S^^- ^ ^™' however, convinced that there must be 

 sudden some profound connexion between the two facts, that 

 ciicufiJ ° great and sudden changes in the circumstances of their 

 stances are Kyes are destructive to organisms, and that organisms 



nsstmC" 



tive. are unable to effect great changes in their habits, except 



very gradually. The proof that there is such a connexion 



