The Great Physiologist of Heidelberg

Natural History, July, 1999 by Stephen Jay Gould

Tiedemann bases his argument entirely on the overlapping ranges of smallest to largest skulls in each race, and we can scarcely deny his correct conclusion that no difference exists between Ethiopians (32 to 54 ounces among 38 skulls) and Caucasians (28 to 57 ounces for a larger sample of 101 skulls). But as I scanned his charts of raw data, I suspected that I might find some interesting differences among the averages for each racial group--the obvious summary statistic (in Tiedemann's time as well as today).

Indeed, as my table and graphs show, Tiedemann's uncalculated mean values do differ--in the traditional order advocated by his opponents, with a gradation from a largest average, for Caucasians; through intermediary values for Malayans, Americans (Native Americans, not European immigrants), and Mongolians; to the lowest value, for his Ethiopian group. The situation becomes even more complicated when we recognize that these mean differences do not challenge Tiedemann's conclusion, even though an advocate for the other side could certainly present this information in just such a manner. (Did Tiedemann calculate these means and not publish them because he sensed the confusion that would then be generated--a procedure that I would have to label as indefensible, however understandable? Or did he never calculate them because he got what he wanted from the more obvious data on ranges and then never proceeded further--the more usual situation of failure to recognize potential interpretations as a consequence of unconscious bias? I rather suspect the second scenario as more consistent with Tiedemann's personal procedures and the actual norms--as opposed to the stated desirabilities--of scientific study in general. But I cannot disprove the first conjecture.)

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My appended graph of Tiedemann's uncalculated data (see "Tiedemann's Data and Ranges," below) does validate his position. The ranges are large and fully overlapping for the crucial comparison of Caucasians and Ethiopians (with the substantially larger Caucasian sample including the smallest and the largest single skull for the entire sample of both groups, as expected). The differences in mean values are tiny compared with the ranges and, for this reason, probably of no significance in the judgment of intelligence. Moreover, the small variation among means probably reflects differences in body size rather than any stable distinction among races. (As previously cited, Tiedemann had documented the positive correlation of brain and body size in asserting the equality of brains in men and women.) His own data indicate the probable correlation of mean differences in brain weight with body size. He divides his Caucasian category into two parts by geography--Europeans and Asians (mostly East Indians). He also states that Caucasian males from Asia tend to be quite small in body size. Note that on the chart of Tiedemann's raw data, which appears on the previous page, the mean brain size for these (presumably smallestbodied) Caucasians from Asia stands at 36.04 ounces, the lowest value of his entire chart, lying well below the Ethiopian mean of 37.84 ounces.