THE MIND OF MAN 281 



deferred instincts which have been evolved by Natural 

 Selection by reason of their utility, and which therefore are 

 common to the whole species, the entire mental difference 

 between the infant and the adult is due to the acquirements 

 made by the latter. One man may have more of this or 

 that instinct; but, since instincts have been evolved, he 

 cannot have different instincts, at any rate if he has not 

 varied very greatly that is, if he is a sane person. On the 

 whole instinct makes the individuals of a species alike, not 

 different. The mental differences between adults, then, are 

 due, first to differences in innate capacity, in innate power of 

 making and utilizing acquirements, and secondly, and to a 

 much greater extent, to differences in the acquirements that 

 are made by virtue of this capacity. This is true also as 

 regards physical structures, but whereas, as we have just 

 seen, use causes physical structures to develop along lines 

 that are rigidly fixed and limited as regards direction and 

 extent, experience may cause the mind to develop to an 

 almost unlimited extent in any one of a million possible 

 directions. The nature of the mental acquirements depends 

 almost wholly on the individual's peculiar environment on 

 his experiences, his opportunities for learning. And, since a 

 difference in acquirement constitutes the main part of the 

 mental difference between the infant and the adult, since 

 the experiences of individuals are never alike and may differ 

 extremely, it is evident that the environment must be a very 

 potent factor in the causation of mental differences. This is 

 obviously true as regards knowledge, for no two men know 

 exactly the same things. It is less obvious, but probably no 

 less true, as regards more subtle mental differences. We 

 often say, when speaking of this or that man, that he is by 

 nature resolute or weak, proud or servile, brave or cowardly, 

 honest or knavish, moral or immoral, merciful or cruel, just 

 or unjust, gentle or violent, morose or genial, buoyant or 

 depressed, sanguine or despondent, intelligent or stupid, 

 broad-minded or bigoted, and so on. We are probably 

 mistaken. There is abundant evidence that characters such 

 as these are dependent mainly, not on germinal differences, 

 but on acquirements. 



450. Mental acquirements may be due to the individual's 

 physical condition. Good health tends to render him 

 buoyant, ill-health to depress him. Gout predisposes people 

 to irritability, chronic liver complaint to despondency. The 

 dyspeptic is often morose. An odd cheerfulness is often 

 shown by the consumptive. Exophthalmic goitre is a cause 



