50 
Vm'iation and Correlation in Brain-Weight 
The mean of the two differences is 74'910, while the observed difference between 
male and female mean brain-weights in the Bohemian " skull " series is 142*014, or 
in other words by selecting from either sex individuals with mean skull length and 
skull breadth equal to those found in the opposite sex, we are able to reduce the 
sex difference in mean brain-weight by about 67 grams, or 47 This result is of 
considerable interest. We can come nearer to the brain-weight of one sex by 
selecting skull length and breadth to the means of that sex than we can by 
selecting stature and age, but still not a great deal nearer. We should on general 
grounds expect that aside from skull capacity, skull length and skull breadth 
would be the two characters whose selection would indirectly modify brain-weight 
the most. Admitting this to be the case there still remains a considerable 
difference to be accounted for. It is interestino' to note that the sexes are brought 
nearer together in brain-weight when males are selected than when the selection 
is from the females. This is explained by the fact that the brain-weight is some- 
what more highly correlated with the skull characters in the males in our series. 
Finally, we may examine the effect of a selection of stature and body-weight on 
the sex difference in brain- weight. The material here comes from the Bavarian 
series, and the prediction is made in the same way as in the other cases ; viz., by 
selecting males with mean stature and body-weight equal to the female means 
and vice versa, and determining the mean brain-weight of the selected groups. 
The results are shown in Table XIII. 
TABLE XIII. 
Probable Male Brain-tueight with Mean Stature and Body-weight 
equal to the Observed Female. 
Eace 
Predicted male 
brain-weight 
Observed female 
braiu-weight 
Difference 
Equation 
Bavarian . . . 
1321 -496 
1218-776 
102-720 
29 
Probable Female Brain-iveight with Mean Stature and Body-weight 
equal to the Observed Male. 
Eace 
Predicted female 
brain-weight 
Observed male 
brain-weight 
Difference 
Equation 
Bavarian ... 
1261-298 
1357-466 
96-168 
30 
Here the better result is obtained by selecting from the females on account of 
the higher correlation between brain-weight and body-weight and brain-weight 
and stature in this sex. The mean of the two differences is 99-444, and the 
observed sex difference in the case is 138-690 gr. So then the differences between 
