A systems-model for the morphological analysis of integration and modularity in human craniofacial evolution

Abstract

In spite of a long history of research in craniofacial biology the extent to which developmental cascades between the brain, the cranial base, and the face influences the evolution, development and variation of the skull, is not clear. This paper discusses aspects of these problems in terms a "systemsmodel" of morphological integration and modularity of human craniofacial morphology. This model proposes analysing morphological variation and evolution of the human skull by considering ontogenetic and evolutionary modifications of modules by local (cranial) as well as general (non-cranial) factors, which implies an organismal view on human skull evolution. For example, the size and shape of brain lobes have local effects on skull shape, moulding lateral basicranial morphology. These effects, which are relatively independent from midline cranial base variation, interact with the position and morphology of the mandible and the postero-superior limit of the ethmo-maxillary complex. Another local factor within the face includes changes of the size and shape of nasal cavity. However, this cranial module is functionally integrated with a more general body system, such as respiratory apparatus and functionally linked with non-cranial factors such as body energetics, size and allometry. This paper suggests that a joint consideration of local and general factors likely improves the development of holistic hypotheses about human craniofacial evolution.