Frontal grooves in African populations: a non-metrical cranial trait analysis

Frontal grooves, first described by Dixon (1904) and later by Ossenberg (1969), are grooves occurring in various number, bilaterally or unilaterally, on the frontal bone of the human skull. All previously published studies have agreed that they are caused by the lack of growth of the supraorbital nerve in relation to the growth and curvature of the frontal bone, whereby the nerve acts as a constricting cord and makes its imprint on the underlying bone. This study attempted to find an alternate explanation for the grooves, arguing that they are too flexible in their growth to make such a mark. This study analyzed over five hundred different skulls, from fourteen geographical areas. Their sex, age, cephalic index, and the number and depth of any frontal grooves was recorded. Frontal grooves occurred significantly more frequently, and in greater depth, on South and West African skulls than on those of any other population (Chinese, East African, Italian, Peruvian, etc.). There was no significant relationship found between cephalic index and the presence or depth of frontal grooves. Previously published data indicate frontal grooves to be an age-stable trait that is more prevalent in females. This study found the opposite of both of these conclusions. Several hypotheses are offered for the significantly higher frequencies of this trait among South and West Africans, including higher incidences of frontal bossing and the production of osteoclasts, and lower cephalic indices.