14 
Variation and Correlatioii in Brain-Weight 
or indices of brain power. It became evident after a time, however, that there 
was not the close and definite relationship between brain-weight and intellectual 
capacity which had been supposed to exist. Individuals of marked intellectual 
power were found in not a few instances to have brain-weights below the average, 
while on the other hand it was not at all difficult to find individuals of very 
mediocre intellectual attainment who possessed brains of unusually large size and 
weight. These results still held even after rough corrections were made for bodily 
size, age, etc. While it is thus evident that brain-weight cannot be taken as 
a close index of intellectual power, holding for individual instances, yet it is clear 
that, considered from the phylogenetic standpoint, increase in brain-weight and in 
psychic capacity have in general gone hand in hand, and the weight of the brain 
increases quite regularly as we go up the taxonomic scale*. 
The present trend of investigation in this subject, is rather from the point of 
view of anthropology than of psychology. Evidently brain-weight is an important 
and interesting anthropological character, and in this field we may expect 
significant results. 
The method of investigation which has been almost universally followed in 
brain-weight work has been to tabulate large masses of statistics of weighings, 
compute means for various groupings, and draw the conclusions which appeared to 
follow from the tabulations and averages. In other words the only statistical 
methods which in most cases have been applied to the data have been those of the 
sociological statistician. Such methods serve fairly well, of course, when only the 
" types " are wanted, but they are quite inadequate for some of the work which 
many neurologists have wished to do in this field. Practically all students of the 
subject have attempted to determine in one way or another the degree of correlation 
which exists between brain-weight and other physical characters and also age. 
Knowledge of these correlations is of course much to be desired. The human 
brain is justly to be regarded as the highest product of organic evolution. Any 
contribution to a knowledge of the laws governing its variation and correlation 
cannot fail to be of the greatest interest. Again, only through a knowledge of the 
degree of the correlation of brain-weight with other characters of the body is it 
possible to make scientifically such suitable corrections for bodily differences 
as will make fair any comparison of the brain- weights of different races, or 
of different groups of the same race. Now, as everyone knows who has 
even an elementary knowledge of statistics, it is possible to make the same 
statistical material lead to quite different conclusions, by grouping it in different 
ways, when the tabulations and averages are the only sources from which 
conclusions may be drawn. As a matter of fact this has happened in work on 
brain-weights. Different investigators, working in different ways, have arrived at 
* Cf. Ziehen, Tb.: "Das Gehirn, Massverhaltnisse," Bardelebeu's Handhuch der Anatomie des 
Menschen, Bd. iv. 1 — 3 Abtheilutig, pp. 353—386, 1899, p. 362 et seq.; and more recently Spitzka, E. A.: 
" Brain-weight of Animals with special reference to the Weight of the Brain in the Macaque Monkey," 
Jour. Comp. Neurvl. Vol. xiii. pp. 9 — 17, 1903. 
