96 ESSAYS OF A BIOLOGIST 



for thought about the thousand and one details of 

 daily conduct, he may be making himself and his 

 wife thoroughly unhappy, ruining his family's 

 chances, and, as a matter of fact, be thoroughly 

 immoral without once suspecting it. 



It is in a very similar way that the militarist, for 

 instance, fortifying himself in the doctrine of the 

 struggle for existence with what he regards as an 

 impregnable sanction for his theories, is in reality 

 acting immorally because not attempting to envisage 

 the whole problem. 



There is one very interesting evolutionary point 

 which well illustrates the difference between pure 

 biology and pure sociology, and yet emphasizes the 

 natural connection between the two. Once again 

 it has a connection with the greater flexibility of 

 human mind. As we have seen, in the lowest animals 

 behaviour is for the most part unvarying, hereditarily 

 determined : the organism is capable of a number 

 of definite reactions, and if these do not suffice to 

 extricate it from difficulties, it perishes. The first 

 step towards gaining flexibility is the power of learn- 

 ing. ' Once bitten, twice shy ' is applicable to all 

 higher vertebrates ; and it is not only the burnt 

 child who dreads the fire (although a study of moths 

 and candles will convince us that * Lepidopteran ' 

 cannot be substituted as subject of the proverb). 



When, as in the higher mammals, the power of 

 learning by experience is rapid, the individual organism 



