XVIII 

 THE EVOLUTION OF MENTAL CHARACTERS 



1. When we originally asked how far changes in the quality 

 of the population accounted for the facts given in the sixth 

 chapter, it was at once obvious that the interest centred in 

 mental changes. Now that we have gained some idea as to 

 what is given in the germinal constitution and as to the influence 

 of the environment in general, we are in a position to come more 

 closely to the main problem. Three questions present themselves. 

 We have to inquire into the facts regarding the stage of mental 

 evolution reached at any one time. This involves making both 

 an estimate as to the extent of the gap between the pre-human 

 ancestor and Palaeolithic man and an examination of the differ- 

 ences in the mental characteristics of the chief living types of 

 man which may be taken roughly to represent stages reached in 

 the three chief periods. We have next to ask if we can account 

 for these facts, and this involves an inquiry into selection, 

 differential fertility, and such other factors as may assist to 

 explain changes in the germinal constitution. Lastly we have 

 to ask how far such changes as have taken place are correlated 

 with the main features of human history. 



To make an estimate of the stage of mental evolution reached 

 by one race as compared with that reached by other races is not an 

 easy matter. To begin with there is the difficulty of discounting 

 the direct influence of the environment. Temperament we found 

 to be peculiarly susceptible to environmental influence. Tempera- 

 ment affects the functioning of other mental characters in a very 

 important manner. ' Effective mental ability ', says Professor 

 Punnett, ' is largely a matter of temperament, and this in turn 

 is quite possibly dependent upon the various secretions produced 

 by the different tissues of the body. Similar nervous systems 

 associated with ' different livers might conceivably result in 

 different individuals upon whose mental ability the world would 

 pass a very different judgment.' ^ Apart, however, from this 



' Punnett, Menddisin, p. 208. 

 2498 U ]j 



