The human species

by A. de Quatrefages

Seven Negro brains weighed by M. Broca gave a mean of 1316 grm. (46·42 oz.). Upon uniting the weights of European brains I find, however, a mean of only 1248 grm. (44·02 oz.), that is almost exactly the average of the White woman. The average weight of adult European brains is 1405·88 grm. (49·59 oz.). But in both races, individual oscillations are very considerable. One of the skulls of the Black race examined by M. Broca weighed 1500 grm. (52·91 oz.); Mascagni had one of 1587 grm. (55·94 oz.), and another of only 738 grm. (26·03 oz.).

The truth is that the European White alone has been seriously examined from the point of view of the estimation of cerebral development by weight. The merit of having furnished the elements of this study belongs incontestably to Rud. Wagner. Uniting the far more important results of his own researches with those of Tiedmann, Sims, Parchappe, Lélut, Huschke and Bergmann, this savant drew up a table containing the weight of 964 brains, which had been directly obtained after removing the coverings; he arranged them in order, commencing with the heaviest and finishing with the lightest. But he had not taken circumstances of sex, age, health, disease, etc., into consideration. The results which he obtained were, therefore, subject to alterations and corrections. M. Broca has accomplished this task. He took 347 cases of healthy brains from Wagner’s table, and carried out his investigations entirely upon them.

A certain number of general propositions rise from all these researches, which may be formulated in the following manner:

1. Under similar circumstances, in other respects, the weight of the brain varies proportionately, or almost proportionately, to the height. According to Parchappe, the average weight of the brains of two groups of men with an average height of 1·74 metre (5·7 feet) and 1·63 metre (5·2 feet), was 1330 grm. (46·91 oz.), and 1254 grm. (44·23 oz.). In this example the differential relation, 6 per cent., is exactly the same for the height of the body and the weight of the brain. This influence of stature enables us to interpret and comprehend the facts brought forward by Mr. Sandford Hunt. From the calculations of this anatomist it would appear that the average weight of the brain of Anglo-American soldiers exceeds the average weight of European brains as deduced from Wagner’s tables; by from 19 to 14 grms. (·67 to ·49 oz.), or from 1·33 to ·99 per cent. But the American anatomist did not take into consideration the difference in stature, which he nevertheless notices. Now, from his calculations, it appears that American soldiers have, in this respect, the advantage over French and English soldiers to an extent of 3 per cent. The increase is, therefore, only apparent, and, indeed, rather points to a relative diminution.

2. Under similar circumstances in other respects, the female brain weighs a little less than the male. M. Broca has shown that this is the case at all periods of life. This difference appears to me, however, to arise almost exclusively from that of the stature of the body. Upon taking the woman as the term of comparison, and representing her height and the weight of her brain by 100, we find 109·43 and 109·34 as the result for the man. The latter relation is that given by Parchappe. M. Broca found 109·63; thus the relative heights are intermediary.

3. The maximum average of the European is observed between the thirtieth and fortieth years. It is then 1262 grms. (44·48 oz.) in the female, and 1410·36 grms. (49·74 oz.) in the male, or, in percentages, 100 and 111·7. The average for the entire period of maturity, between 30 and 50, is 1405·88 grms. (49·59 oz.) in the male, and 1261·5 grms. (44·5 oz.) in the female.

4. Beyond this maximum the weight of the brain appears to decrease continually, and in a more or less constant manner. Such, at least, is the result arising from calculations bearing upon decennial intervals, which show a constantly decreasing average in the male, as well as in the female. There is probably some relation between this diminution and that of the horizontal circumference of the cranium and the development of the frontal sinuses, observed long ago by Camper.

5. In the European White, a brain, to be capable of performing its functions, must weigh at least 975 grms. (34·39 oz.) in the female, and 1133 grms. (39·96 oz.) in the male. These figures are the result of the discussion upon Wagner’s table; they are, however, too high, to judge from some of Hunt’s calculations. In the Bosjesman and Australian, and probably in many other races, the weight of the brain may descend as low as 907 grms. (31·99 oz.), without the intellectual faculties being destroyed.

Let us add that this organ may, moreover, fall much below this weight without causing cessation of life, or even the absolute disappearance of the intelligence, as in some microcephali. The smallest brains which have ever been weighed are those of Teite, quoted by Wagner, 300 grms. (10·58 oz.), and that of the woman who formed the subject of a memoir by Gore, 283·75 grms. (10 oz.). These brains are appreciably inferior in weight to those of the gorilla and orang.

6. In the European White, the maximum weight of a healthy brain perhaps reaches 2231 grms. (78·69 oz.) (Cromwell), or even 2238 grms. (78·94 oz.) (Byron). But there is not the certainty we should wish for about these figures. The weight of Cuvier’s brain is, however, attested by the post-mortem examination conducted by Professor Bérard; it is 1829·96 grms. (68·43 oz.). Mr. Sandford Hunt quotes another at 1842 grms. (65·32 oz.). We may regard these figures as indicating the superior limit which can be attained by the brain in the White race without the general health appearing to be affected.