82 
Variation and Correlation in Brain-Weight 
14. Summary. 
Some of the more important general conclusions of a study of five series of 
brain-weighings, representing Swedish, Hessian, Bavarian, Bohemian, and English 
sub-races of man and including altogether the weights of 2100 adult male and 
1034 adult female brains, may be summarised as follows: 
1. There are definite racial types in brain- weight. The differences between 
racial groups in this character are only in part to be accounted for by differences 
in other characters of the body. 
2. The series studied exhibit a very fair degree of homogeneity. 
3. In respect to variability the characters, brain-weight and skull capacity are 
sensibly equal. The coefficients of variation for brain-weight are intermediate in 
value between those which have been determined for skeletal characters in man 
on the one hand, and those for the weights of the viscera and for various physio- 
logical characters on the other hand. 
4. Having regard to the size of the present series we conclude that variation 
in weight of the bi'ain m-Ay for practical purposes be considered to follow the 
" normal " law of the distribution of errors. If the mean and the mode do not 
exactly coincide the mean will be slightly greater than the mode in brain-weight 
frequency distributions. 
5. The correlation of brain-weight with age, stature and body- weight, is in all 
cases low. 
6. The correlation of brain- weight with skull length and skull breadth is, in 
comparison with the other characters studied, fairly high, and is for both skull 
length and breadth positive. 
7. The sexual differences in mean brain- weight are practically constant in all 
the races studied, whether considered absolutely or relatively. 
8. Only a part of the sexual difference is to be accounted for by differences 
between the sexes in other bodily characters. 
9. The sexes are equally variable in respect to brain-weight. 
10. The weight of the brain tends to be more highly correlated with other 
characters in the female than in the male. 
11. The correlation of bi'ain- weight with age is negative. The regression of 
brain-weight on age is, so far as can be determined fi'om our present series, linear 
throughout the period of life comprised between the ages 20 to 80. In other 
words, there is a steady decline in the weight of the brain with advancing age, 
beginning at about the twentieth year and continuing throughout adult life. 
