December 28, 1905] 



NA TURE 



Biometrika 1 published a few months ago are par- 

 ticularly welcome ; they lay a foundation for an exact 

 knowledge of this subject. 



For a hundred years and more anatomists have 

 sought to establish a formula by which the mental 

 ability of any individual could be predicted from an 

 examination of the head or brain. The problem was 

 found to be beset with difficulties and extremely com- 

 plex. How was mental ability to be standardised and 

 measured? Is the ability shown by any individual a 

 fair and full manifestation of his endowment, or may 

 it be presumed that much is latent and potential? 

 Are all the nerve structures within the cranial cavity 

 equally concerned in the manifestation of a simple 

 mental process, or is the organ* of the mind confined 

 to a part or parts of the brain ? At an early date it 

 was discovered that the size of the mammalian brain 

 depended to a considerable extent on the size of the 

 body; age and sex, too, were found to influence its 

 weight. The weight of the brain was found to vary 

 widely from individual to individual without any 

 evident relationship to mental ability, so that most 

 scientific men came to share the opinion of the un- 

 scientific, that neither the shape nor the size of the 

 head, the volume or weight of the brain, could provide 

 any but the most uncertain indication of mental 

 status. Those who sought a key in the arrange- 

 ment and complexity of the convolutions have not 

 been more successful. Yet the belief that there is a 

 close relationship between the relative size of the brain 

 and degree of intelligence cannot be abandoned, for 

 it is founded on a study of comparative anatomy. 

 Amongst primates, for instance, it is found that those 

 members which most nearly approach man in size and 

 complexity of brain also most closely resemble him 

 in their mental processes. It is probable, as suggested 

 by Prof. Ray Lankester (Nature, p. 624, April 26, 

 1900), that the increase in brain-weight is correlated 

 with the substitution of voluntary or conscious for 

 reflex, instinctive or automatic mental processes, or, 

 in other words, the increase of brain-weight which is 

 seen in the highest primates is the substratum of that 

 mental qualitv which he has named " educability "; 

 there is also the widespread belief that eminent men 

 have relatively large heads. An examination of the 

 heads of sixty distinguished men led Dr. Beddoe to 

 the conclusion that " Intellectual distinction is 

 generally the concomitant of largeness of brain, 

 though there are numerous exceptions " (Journ. of 

 the Anthropological Institute, p. 277, 1904). The 

 method by which Dr. Beddoe sought to establish a 

 correlationship between intelligence and skull capacity 

 is regarded by Lewenz and Pearson as " quite 

 fallacious. To begin with he selects a formula — 

 by guesswork — which is theoretically incorrect " 

 (Biometrika, p. 392, vol. iii., 1904). To sum up, 

 anthropologists have not been able to establish, by 

 the methods commonly in use, that there' is any direct 

 connection between the size of brain and special 

 manifestations of human intelligence. 



Turning now to the biometricians, their conclusions 

 have the advantage of being founded on extensive 

 collections of data, and reached by methods which are 

 mathematically sound. In the number of Biometrika 

 cited at the commencement of this article, Dr. Ray- 

 mond Pearl gives the results of a biometrical analysis 

 of 2100 adult male and 1034 adult female brain- 

 weights, belonging to five races, Swedish, Bavarian, 

 Hessian, Bohemian, and English. Although the 



1 Biometrika, vol. iv. , pans i . ii., Tune, 1905, (1) " Variation and Corre- 

 lation in Brain-weieht,'' by Dr. Raymond Pearl (with twenty-three 

 diagrams in the text); (2) " A Study of the Relations of the Brain to the 

 Size of the Head.' by Dr. Reginald J. Gladstone (with plates ii., iii., and 

 five figures in the text) 1(3) "On the Bionutric Constants of English 

 Brains-eights." by Mr T. l.'lakeman, assisted by Miss Alice Lee and 

 Prof. Karl Pearson, F.R.S. (with six figures in the text). 



NO. 1887, VOL. 73 J 



matter was only a side-issue in his investigation, he 

 sums up his conclusion as to the correlationship 

 between brain-weight and intelligence thus : — " There 

 is no evidence that brain-weight is sensibly correlated 

 with intellectual ability. The limits of this correlation^ 

 have been shown to be not closer than o and +o'6. ' r 

 Here are the conclusions of other biometricians : — 

 " There is no marked correlation between skull 

 capacity and intellectual power " (Dr. Alice Lee). 

 " We find the correlation sensible but so small that 

 it is impossible to base any prediction from the size 

 of the head as to general intelligence " (Lee, Lewenz, 

 and Pearson, quoted from Biometrika, p. 392, vol. 111., 

 1904). There are certain circumstances, too, which 

 must be taken into account. From about the age of 

 twenty onwards the weight of the brain gradually 

 decreases, a diminution which is not, as a rule, 

 accompanied by a decrease of intelligence. Nor does 

 the mean brain-weight of a race correspond to the 

 mean intelligence of that race. Of the five races in- 

 vestigated by biometricians, the English have the 

 smallest mean brain-weight. The mean of the adult 

 Englishman is 27 grams less than the Bavarian mean, 

 57 grams less than the Hessian mean, 65 grams less 

 than the Swedish mean, and 120 grams less than the 

 Bohemian mean. " The order of racial average 

 brain-weight is very far from the order of average 

 racial intelligence. Nor is the order bettered if we 

 allow in any manner for stature " (Blakeman). On 

 the data at present available, one must come to the 

 conclusion, apparently anomalous, that a big brain, so 

 far as the manifestation of intelligence is concerned, 

 has very little if any advantage over a small brain. 

 The explanation of that anomaly lies with the experi- 

 mental physiologist and psychologist. Meanwhile it 

 is well to remember that under the title of_ brain- 

 weight is grouped a complex of organs which are 

 diverse in structure and in function. 



If there is so little correspondence between brain- 

 weight and brain-function the apparent preponderance 

 of the man's over the woman's brain in weight and 

 size loses much of its significance. It is now possible, 

 thanks to the labours of the biometricians, to speak 

 with a degree of accuracy and assurance as to the 

 extent of that preponderance. The sexual difference 

 in mean brain-weight is least among the English 7 

 the preponderance of the male in England is 100 

 grams (Pearson, from combined data) or 103 grams- 

 (Blakeman, from Gladstone's data); in Hesse 132 

 grams, in Bavaria 142 grams, in Bohemia 144 grams, 

 in Sweden 147 grams, and in France 181 grams. In 

 round numbers, the male preponderance is from S per 

 cent, to 13 per cent. Amongst gorillas the male 

 preponderance is 17 per cent., amongst orangs 13 per 

 cent., amongst chimpanzees 6 per cent., and amongst 

 gibbons 8 per cent., so that the human sexual differ- 

 entiation is approximatelv an average amount for a 

 higher primate. How far is the male preponderance 

 due to greater bodv size? The conclusions reached 

 by biometricians are the following :— " Differences 

 iii stature and age account for less than one-third of 

 the observed sex-difference in brain-weight " (Ray- 

 mond Pearl). " On the whole, as far as present 

 evidence goes, we can safely conclude that there is 

 no sensible relative difference in the brain-weights 

 of man and woman, the absolute differences observed 

 are quite compatible with the differences which result 

 from the relative sizes of the two sexes. . . . While 

 our results thus apparently contradict those^ of Pearl 

 on p. ^1 of this Journal (Biometrika, vol. iv., 1905) 

 the contradiction is only on the surface, for we have 

 been able to use a far more complete system of 

 physical measurements " (Blakeman, Lee, and Pear- 

 son). Yet if the writer has rightly grasped the 



