22 Comparative Conceptions 



at which what may be called ' comparative ' questions 

 arise. By this I mean points at which the interpreta- 

 tion of a series of facts has been fairly made out, or the 

 facts at least formulated, on one side of the two parallel 

 series, and we may properly ask how far the same or 

 an analogous interpretation or formulation is possible on 

 the other side. For example, the law of natural selection 

 from spontaneous variations, which makes use of the 

 criterion of fitness or utility only what can we say of 

 mental evolution from this point of view ? We have 

 here to apply a biological conception directly to the 

 mental. Again, in development the mind seems to pro- 

 gress by a certain function of selection by which it brings 

 itself into better accommodation to a complex mental and 

 physical environment. Here is a certain formulation on 

 the mental side, a function so well recognized that the 

 criterion of consciousness in an organism is often said to 

 be the exhibition of a ' selective ' reaction. What now 

 can the biologist do with this in his theory of organic 

 development ? 



Both of these instances are enlightening for the deri- 

 vation of what I am calling * comparative conceptions.' 

 The union of the two seems to require that the brain 

 variations by which evolution proceeds be of such a sort 

 that their very utility that for which they are se- 

 lected is in the line which mental development by a 

 selective function in each generation acquires. Now, in 

 fact, we find this requirement fulfilled in the evolution, 

 by variation and natural selection, of increasing plasticity 

 of nervous structure. By this, not only does it appear 

 that mental evolution progresses by variation, keeping 

 pace with organic (a correlation in evolution), but also 



