THE INHERITANCE OF FAMILY TRAITS 65 



17. General Bodily Strength 



-- Like other bodily traits general stren^tli is clearly in- 

 herited. This appears repeatedly in our records. An ex- 

 ample is given in Fig. 29. 



■jO DtO 



Fig. 29. — Inheritance of muscular strength. I, 1, of great physical strength. 

 His son II, 3, was likewise possessed of unusual strength. His elder son in 

 turn was athletic but became dissipated. F. R.; St. L 



18. General Mental Ability 



The general mental ability of a person is a vague concept 

 which is, however, in common use. We speak of a man as 

 weak minded, as of mediocre ability, as exceptionally able 

 without attempting a closer analysis of the subject. 



General mental ability, like stature and weight, under- 

 goes a progressive development so that in studying its 

 heredity we must compare it in adult persons or else measure 

 it by the deviation the person shows from the normal of his 

 age. Thus we may call "weak mindedness" such a defect 

 as would keep a child of 10 in a school grade where the other 

 children are 6 or 7; a child of ''mediocre" ability is not 

 more than two years behind the average grade for his age; 

 ''exceptionally able" would imply, say, two years in advance 

 of children of his age. A series of tests (the Binet-Simon 

 tests) have been devised to gauge mental abiUty by gauging 

 a variety of capacities such as general information, ability 

 to count and to repeat phrases, to recognize names and 

 describe common things and to make fine sense discrimina- 



