232 INBEEEDING AND OUTBKEEDING 



gation and recombination of several factor pairs. This in 

 general is the interpretation given the inheritance of gen- 

 eral mental ability or inherent ability in music, literature, 

 art, or mathematics. We simply know that such abilities 

 are inherited in some complex way, which, it is logical to 

 assmne, is Mendelian. We know the fact from pedigrees 

 of families in which ability of a particular kind is very 

 marked; we make the assumption from such circumstan- 

 tial evidence of the generality of Mendelian phenomena 

 as has been presented in abstract in this volume. 



Having this basis, what shall be said of the effect of 

 inbreeding and crossing on the individual! It would be 

 easy to point to the conclusions reached when discussing 

 domestic animals and plants, and say: **The same line of 

 reasoning holds for man; draw your own conclusions. ' ' 

 But this is hardly satisfactory. It is true enough, as a 

 generality, to point to the desirability of some mating out- 

 side a particular line in order to assure physical vigor by 

 complementary hereditary factors meeting each other, or 

 to mention the possibility of undesirable characters being 

 brought to light in some strains and of desirable char- 

 acters being added in others by inbreeding. One would 

 hardly feel this to be an answer to the question. If 

 the study of heredity has resulted in an advance in knowl- 

 edge having some practical value, it ought to be possible 

 to make a more definite analysis of the facts as applied to 

 the human race. 



Let us ask first, What is ability in the human race, and 

 what the evidence that it is inherited ? A fair definition of 

 ability may be given in the phrase, * * skill in accomplish- 

 ment, ' ' and this puts considerable emphasis on mentality. 

 We all desire a healthy mind in a healthy body, but a 



