1 66 MENDELISM CHAP. 



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 ot 

 mental ability may depend for its manifestation, not 

 so much upon an essential difference in the structure 

 of the nervous system, as upon the production by 

 another tissue of some specific poison which causes 

 the nervous system to react in a definite way. We 

 have mentioned these possibilities merely to indicate 

 how complex the problem may turn out to be. 

 Though there is no doubt that mental ability is 

 inherited, what it is that is transmitted, whether 

 factors involving the quality and structure of the 

 nervous system itself, or factors involving the pro- 

 duction of specific poisons by other tissues, or both 

 together, is at present uncertain. 



Little as is known to-day of heredity in man, 

 that little is of extraordinary significance. The 

 qualities of men and women, physical and mental, 

 depend primarily upon the inherent properties of the 

 gametes which went to their making. Within limits 

 these qualities are elastic, and can be modified to a 

 greater or lesser extent by influences brought to bear 

 upon the growing zygote, provided always that the 

 necessary basis is present upon which these influences 

 can work. If the mathematical faculty has been 

 carried in by the gamete, the education of the zygote 

 will enable him to make the most of it. But if the 

 basis is not there, no amount of education can trans- 

 form that zygote into a mathematician. This is a 

 matter of common experience. Neither is there any 



