DATA FOE THE PEOBEEH OF EYOLUTIOX IX MAX. 
259 
sensible correlation between skull capacity and intellectual ability will tend to weaken 
current conceptions as to a relationship between brain weight and intellectual ability. 
The whole problem of the relation of size of head to intellectual distinction as judged 
by popular standards is under investigation from wider data ; meanwhile, I think we 
may conclude— 
(i.) That there is no marked correlation between skidl capacity and intellectual 
power in the case of either sex alone. 
(li.) That, brain weight must have a very considerable correlation with skull 
capacity, and, therefore, our data present nothing to encourage the belief that 
there is a relation between brain weight and brain power. 
(iii.) That arguments based on the relative brain weight of the two sexes as 
showing relative brain power require a more solid quantitative basis than they 
at present exhibit.^ 
(iv.) That such arguments as those of A. R. Wallace against the evf)lution of 
man’s intellectual powers by aid of natural selection turn wholly on the size of 
the brain. But it would not aj^pear from the above results that skull capacity 
at any rate is a character closely correlated with intellectual ability in the indi¬ 
vidual, and, therefore it is quite conceivably not correlated with racial ability. 
So soon as data are forthcoming connecting the skull capacity with brain weiglit^ 
or .still better, brain weight with head measurements, we sliall he in a position to 
reconstruct Ijrain weight from head measurements. I do not see that the error of 
the determination is likely to he much larger than that found in the case of skull 
capacity, hut if it reached 8 to 9 in.stead, say, of 3 to 4 per cent., it would .still he 
sufficiently approximate to give (piite reasonable results for large numbers of 
individuals classified into big groups according to their ability. It is, I hold, only by 
such methods that we can hope to reach any quantitative certainty of a relation 
between brain power and brain size. Personally I am inclined to hold with Professor 
Pearson that the complexity of the convolutions of the lu’ain, and the variety and 
efficiency of its commissures, rather than its actual size, are the characters we might 
expect to differentiate race from race and sex from sex, and to have developed with 
man’s civilisation.! 
I am not unaware that a correlation has often been asserted between brain weio-ht 
and ability on the ground of the actual measurement of the brain weights of a 
number of men of genius. But what is the average of such brains compared with ? 
The average brain weight of the bodies which reach the dissecting rooms of our 
hospitals, a large proportion of which belong to the emaciated and worn out. 
Probably on the .same basis a correlation between genius and body-weight could 
* Before questioning whether man or woman (relatively to stature, body weight, or other character) has 
the greater brain weight, it seems desirable to settle whether brain weight in either sex alone, absolute!}', 
or relatively to some other character, has anything to do with intellectual ability. 
t ‘Grammar of Science,’ 2nd ed., p. -539. 
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