Finally, this error did not «demote» blacks: the rank ordering of groups by
average cranial capacity remains «White / Indian / Black» whether «Indians» are 80 in3 or 82 in3.
In Morton's initial seed - based 1839 study, «Caucasians» had the largest
average cranial capacity (87 in3) followed by «Mongolians [Asians]» (83 in3), «Malays [Island Southeast Asia]» (81 in3), «[Native] Americans» (80 in3), and «Ethiopians [Africans]» (78 in3)[8].
Gould's claim that Morton had mismeasured crania based on race derived from his comparison of Morton's seed - based and lead shot — based measurements, with different races experiencing different changes in
their average cranial capacity between the two methods [1].
The changes in
average cranial capacity from Morton's seed - based measurements to shot - based measurements can not be reconstructed with any certainty, incorporate erroneous seed measurements made by Morton's assistant, yielded a broad range of changes (− 10 to +12 in3) hidden by Gould's mean, and are confounded by the shifts in sample composition (circa 50 %) between the two rounds of measurement.
For example, Gould published an erroneously low Caucasian
average cranial capacity, and an erroneously high Native American average, due to mistakes in how he used Morton's data.
Not exact matches
Morton did not consider the influence of sex or stature on
cranial capacity, but it would have been impossible for him to use those parameters to bias the
averages he reported (see Box 3).
In this regard, it is essentially impossible for Morton to have exploited sexual differences in
cranial capacity to alter population
averages.
It is doubtful that Morton equated
cranial capacity and intelligence [6], [13], calling into question his motivation for manipulating
capacity averages.
In particular,
cranial capacity variation in human populations appears to be largely a function of climate, so, for example, the full range of
average capacities is seen in Native American groups, as they historically occupied the full range of latitudes [18].