CHAPTER IV 



INHERITANCE OF MENTAL CHARACTERS 



IN MAN 



When we consider mental and moral traits, the 



evidence of inheritance in many cases appears sound 



and beyond dispute, although in the matter of human 



character it is less certain how far the accidents of 



early environment ma}^ suppress or seriously modif\' 



the expression of various inherited traits. Here 



we are in a region where the structural basis of the 



developed inheritance is so tenuous, and the contact 



with the environment so intimate — character and 



environment becoming so mutually involved and 



interpenetrating — that it is conceivable that the laws 



applying to structural characters are not applicable 



with the same rigidit}- to the elements or methods 



of reaction that go to make what we call human 



character. Nevertheless, critical students of the 



subject speak with one voice, and it is quite certain 



that heredity plays an equally important role here 



also. Indeed, the statistical results of Pearson (1904) 



indicate that for siblings the intensit}' of resemblance 



is as great for mental as for physical traits. He chose 



eight physical characters — namel}^ health, e3'e colour, 



hair colour, curliness of hair, cephalic index, head 



length, auricular height, and athletic power — and 



eight " mental " characters: vivacity, assertiveness, 



introspection, popularity, conscientiousness, temper, 



ability, and handwriting. While many of these 



characters are not definite enough for anything 



like accurate measurement, and therefore have no 



decisive value, yet the coefficient of correlation 



145 10 



