Unsolved problems in comparing brain sizes in Homo sapiens

When brain size is compared across taxonomic levels, there is a clear relation between body parameters and brain size. It is generally stated that the correlation between brain size and body parameters becomes very small at the species level (Aboitiz, 1996), but this is not the case for Homo sapiens where there is a strong correlation between brain size and body size across racial groups that differ in body size. The control for body size across racial groups (and sexes) is rendered difficult because bodies do not just differ only in height and weight. Within groups different studies show weak and inconsistent brain size/body height correlations. A better understanding of brain size/body height relations must await better quality data and a better understanding of how exactly body parameters should be scaled between groups and sexes. We attribute the clear between-group and weak within-group correlations to the large variety of body sizes and body types in our species, a variety which is only equalled in selectively bred species of animals. At present, there is no meaningful basis for the comparison of brain sizes within and between racial groups and sexes.