no THE TREND OF THE RACE 



While it is recognized by nearly all competent students that 

 mental ability is inherited, the precise method of its inheritance is 

 not thoroughly estabUshed. Heritable characteristics present 

 very different amounts of purely somatic or fluctuating varia- 

 bility and it would seem not improbable a priori that superior 

 mental endowments depending, as they do, upon the delicate and 

 intricate organization of the brain may be subject to such varia- 

 bility to an unusual degree. A child of good ancestry but exposed 

 while in utero to the influence of malnutrition, alcohol, or the 

 toxins of disease at the time when the delicate architecture of its 

 brain is being built up may fall considerably short of its normal 

 expectation in intellectual development. But notwithstanding its 

 intricate structure and the apparent ease with which the delicate 

 balance of its organization might be upset, the nervous system is 

 reproduced in successive generations with a remarkable degree 

 of fidelity, both as regards its external connections and its internal 

 mechanism. Possibly the fluctuating variations in the nervous 

 system may be in part responsible for the fact that the parent- 

 ofTspring and fraternal correlations in the inheritance of mental 

 traits are usually found to be somewhat below those observed 

 for various physical characters. But there are other reasons 

 which might plausibly be assigned also. Although fluctuating 

 variability may affect the basis of mentality somewhat more than 

 it affects eye color or cephalic index it is not sufficient gretv^ly to 

 obscure the facts of mental inheritance, or to reduce very mark- 

 edly the coefficients of mental resemblance between near relatives. 



Is the inheritance of mental traits in accordance with Men- 

 del's law? The question is one of peculiar difficulty since mental 

 traits, as a rule, do not present the sharply definable and discrete 

 features that often characterize the physical pecuHarities of the 

 body. Common observation, however, yields abundant evidence 

 of the alternative inheritance of mental characteristics. Almost 

 every family includes children with different aptitudes, disposi- 

 tions, and tastes that manifest themselves from early infancy. 

 In their mental characteristics children resemble now the father, 

 now the mother or some grandparent or other relative. Many 



