In hominid evolution, the shape of the inner frontal bone in the median sagittal plane has, in contrast to the outer vault, not changed since at least the Plio-Pleistocene (Bookstein et al., 1999). Nonetheless, inner vault size increased significantly (by ∼ 11%) while the size of the outer frontal profile did not. Thus, two of the more interesting questions to pose are: ‘At which other positions of the skull have major shape and size changes taken place?’ and ‘Could it be that the exocranium is involved in shape changes while the endocranium is involved in size changes?’. We approach these questions by analyzing general shape and size of both the exo- and endocranium in the median sagittal plane. Importantly, because the inner surface of the braincase provides information concerning brain evolution (Jerison, 1973) and because of the synevolution of cerebellar and frontal lobes (Seidler et al., 1997), our investigation also includes the occipital bone.

Geometric relations in the median-sagittal plane

Our sample includes 21 crania of modern humans of both sexes (10 females, 11 males): 15 from Central Europe, two San and two Bantu, and two Papuans. To these we added the stereolithographs of three mid- Pleistocene fossil hominid crania (Seidler et al., 1997): Kabwe (Broken Hill 1; Woodward, 1921), Petralona (Kokkoros & Kanellis, 1960), both of uncertain age – but probably in excess of 200 000 years old; and Atapuerca SH5 cranium (Arsuaga et al., 1993), about 300 000 years old.