Speech and the retardation of the human mandible: A Bolkian view

Abstract

Louis Bolk (1866–1930) considered animal evolution as an orthogenetic process, with the human gestalt as a central directing factor. He developed this view to explain the pronounced retardation of human ontogeny. I have argued that retardation leads to proportionally stronger development of ontological latecomers (“hypermorphosis”). This principle is illustrated in this article by the example of the human mandible, the development of which is dominated by a distoproximal gradient. With respect to this gradient three main subsystems can be distinguished: the dental arch (distal), the mandibular base (intermediate) and the ramus (proximal). The dental arch is preponderant in the young mandible. In a later stage, the mandibular base grows beyond the dental system, and the chin appears. The growth of the ramus is belated even with respect to the mandibular base. Therefore the adult human mandible has a small tooth row, a protruding mandibular base (chin), and a high ramus. The main particularities of the human mandible thus follow from its being a retarded structure. Further, the retardation effects shaping the human mandible are embedded within a cluster of comparable effects molding the human body as a whole and culminating in the appearance of the faculty of speech. This observation seems to corroborate the orthogenetic views of Bolk.