142 On the hiheritance of the Mental and Moral Characters in Man 
Now what are we to understand hy "believing" or "not believing" in the 
value for anthropological purposes of any character ? Surely the main point for 
such purposes is the question of whether or no it be inherited and have small 
variability within the group ? I don't think if we look at Table II. we shall find 
the cephalic index worse than other head measurements, especially if we stick to 
one sex. It has an inheritance coefficient of about "5, just what for practical 
purposes we have found for other physical characters. 
So far we have seen surprising uniformity in the inheritance of the measurable 
physical characters. How are we to extend our results to physical characters not 
capable of accurate measurement, and to psychical characters ? Clearly the whole 
problem turns on this : Can we find the steepness or slope of this regression line 
without all the paraphernalia of the correlation table and the means of arrays ? 
The answer is : Yes ; providing we assume a certain distribution of frequency for 
the character in human populations. This distribution of frequency is given by 
the Gauss-Laplacian normal curve of deviations from the mean. Grant this 
distribution, and by very simple classifications indeed we can determine the 
steepness of the regression line. Now the problem before us is the following 
one : — Is this assumption legitimate ? It is certainly not true for organs and 
characters in all types of life. But it really does describe in a remarkable manner 
the distribution of most characters in mankind. We have shown that within the 
limits of random sampling, it is very true for a great variety of characters in the 
human skull*. Dr Macdouell has demonstrated it also for measurements on 
criminals, and you can be fairly convinced of its suitability by looking at one or 
two diagrams. Diagram VI. gives the distribution of nearly 2000 boys in cephalic 
Diagram VI. Bistrihution of Cephalic Index in 1982 
300 
280 
260 
240 
220 
^200 
S 180 
0 160 
£ 140 
<S 120 
UJ 100 
1 
— 1 
! 
1 
J\ 
-f 
69 70 7i 72 73 74 75 76 77 78 79 80 81 82 83 84 85 
CEPHALIC INDEX 
87 88 89 90 91 37 93 
Biometriha, Vol. i. p. 443. 
