26o THE POPULAR SCIENCE MONTHLY. 



consistently maintained tliroughout all orders of races, from the lowest 

 to the highest whether, say, the Australian differs in this respect 

 from the Hindoo, as much as the Hindoo does from the European. Of 

 secondary inquiries coming under this sub-head may be named several : 

 (a.) Is this more rapid evolution and earlier arrest always unequally 

 shown by the two sexes ; or, in other words, are there in lower types 

 proportional differences in rate and degree of development, such as 

 higher types show us ? (i.) Is there in many cases, as there appears 

 to be in some cases, a traceable relation between the period of arrest 

 and the period of puberty ? (c.) Is mental decay earlier in proportion 

 as mental evolution is rapid ? (d.) Can we in other respects assert 

 that, where the type is low, the entire cycle of mental changes be- 

 tween birth and death ascending, uniform, descending comes within 

 a shorter interval '? 



4. Relative Plasticity. Is there any relation between the degree 

 of mental modifiability which remains in adult life, and the character 

 of the mental evolution in respect of mass, complexity, and rapidity? 

 The animal kingdom at large yields us reasons for associating an in- 

 ferior and more rapidly-completed mental type with a relatively auto- 

 matic nature. Lowly-organized creatures, guided almost entirely by 

 reflex actions, are in but small degrees changeable by individual ex- 

 periences. As the nervous structure complicates, its actions become 

 less rigorously confined within preestablished limits ; and, as we ap- 

 proach the highest creatures, individual experiences take larger and 

 larger shares in moulding the conduct : there is an increasing ability 

 to take in new impressions and to profit by the acquisitions. Inferior 

 and superior human races are contrasted in this respect. Many trav- 

 elers comment on the unchangeable habits of savages. The semi- 

 civilized nations of the East, past and present, were, or are, charac- 

 terized by a greater rigidity of custom than characterizes the more 

 civilized nations of the West. The histories of the most civilized 

 nations show us that in their earlier times the modifiability of ideas 

 and habits was less than it is at present. And, if w^e contrast classes 

 or individuals around us, we see that the most developed in mind are 

 the most plastic. To inquiries respecting this trait of comparative 

 plasticity, in its relations to precocity and early completion of men- 

 tal development, may be fitly added inquiries respecting its relations 

 to the social state, which it helps to determine, and which reacts 

 upon it. 



5. Variahility. To say of a mental nature that its actions are ex- 

 tremely inconstant, and at the same time to say that it is a relatively 

 unchangeable nature, apparently implies a contradiction. When, 

 however, the inconstancy is understood as referring to the manifesta- 

 tions which follow one another from minute to minute, and the un- 

 changeableness to the average manifestations, extending over long 

 periods, the apparent contradiction disappears ; and it becomes com- 



