In a previous post, I had assumed Ashkenazi Jews had larger brains than white gentiles, given that they average 10 IQ points higher, and given that brain size has a direct causal effect on IQ.  But an HBD blogger named “n/a” has just showed us a source saying otherwise:

The Jews: A Study of Race and Environment
By Maurice Fishberg

One of the methods of determining the volume of the brain case, and approximately the weight of the brain, is the determination of the cranial capacity. Very few direct measurements of this kind have been taken, because only few Jewish skulls have found their way into anthropological museums, where they could be studied carefully. But from the few studies of this character that have been made, it appears that the Jews are somewhat at a disadvantage. Lombroso’s studies of the Jews in Turin, Italy, which were made in an indirect fashion, showed that the Jews have a smaller cranial capacity than the Catholics of that city.2 Weinberg collected measurements of seventeen Jewish skulls in various museums of Europe, which were made properly, and are not approximations. The average cranial capacity was 1421, which is about thirty to forty below the average cranial capacity of the population of Europe. Of course the small number of skulls thus measured is not sufficient to draw positive conclusions.

As to the weight of the brain, there are also very few observations on record. The author knows only of twentythree Jewish brains reported by Giltchenko,3 four by Weisbach,4 and three by Weinberg.5 The average weight of these brains, as calculated by Weinberg, was 1320.4 gm. Since the average weight of the brain of the European is 1350 gms., the brain of Jews is rather lighter by 30
gms. , or nearly one ounce. Considering that the Jews are shorter of stature than the average Europeans, it would be expected that their brain should also be smaller. But, as Weinberg points out, the average for Germans was found to be 8.22 gm. of brain tissue for each centimetre of stature, while for the Jews it is only 8.05 gms. This shows the Jewish brain lighter not only absolutely, but also relatively.

It seems strange that Ashkenazi Jews could have evolved such high IQ so quickly, yet not seen a rise in brain size given its direct independent causal effect on IQ.  Is this evidence that the high Jewish IQ is cultural, not biological?  On the other hand, as The New York Times reported, Ashkenazis do have certain genetic diseases indicative of high IQ, so perhaps that was enough?