170 MENDELISM chap. 



this due to the inheritance of a particular mental apti- 

 tude, or is it an instance of general mental ability 

 displayed in a field rendered attractive by early 

 association ? We have at present very little definite 

 evidence for supposing that what appear to be 

 special forms of ability may be due to specific 

 factors. Hurst, indeed, has brought forward some 

 facts which suggest that musical sense sometimes 

 behaves as a recessive character, and it is likely 

 that the study of some clean-cut faculty such as the 

 mathematical one would yield interesting results. 



The analysis of mental characters will no doubt 

 be very difficult, and possibly the best line of attack 

 is to search for cases where they are associated with 

 some physical feature such as pigmentation. If an 

 association of this kind be found, and the pigmenta- 

 tion factors be determined, it is evident that we 

 should thereby obtain an insight into the nature of 

 the units upon which mental conditions depend. 

 Nor must it be forgotten that mental qualities, such 

 as quickness, generosity, instability, etc. — qualities 

 which we are accustomed to regard as convenient 

 units in classifying the different minds with which 

 we are daily brought into contact — are not neces- 

 sarily qualities that correspond to heritable units. 

 Effective mental ability is largely a matter of tem- 

 perament, and this in turn is quite possibly dependent 

 upon the various secretions produced by the different 

 tissues of the body. Similar nervous systems associ- 

 ated with different livers might conceivably result in 

 individuals upon whose mental ability the world 

 would pass a very different judgment. Indeed, it is 

 not at all impossible that a particular form of 



