Neandertal Craniofacial Growth: An Ontogenetic Model

This research seeks to develop a model, using modern fetal crania, of Neandertal craniofacial growth. An argument is made that the developmental approach offers greater insight into Neandertal adaptive morphology than the standard functional models. Discussion of the relation between allometry and heterochrony is followed by a general genetic overview and a description of modern fetal craniofacial growth. These patterns are then extrapolated to the Neandertal condition.

Samples for this work consist of modern fetal crania, three modern adult samples, one sample of early modern humans and a sample of Neandertal adults. Principle components analysis was utilized, as was least squares and reduced major axis regressions. A technique was devised where derivatives were taken from polynomials generated from multiple regression.

The results would indicate that the posterior cranial base, and not the anterior base, has the neural like growth pattern. The anterior base has a growth pattern similar to that of facial length and facial height. Using pattern of morphogenesis and known principles of cartilage kinetics, a model of Neandertal craniofacial growth was created. Emphasis was placed upon the effects of global growth acceleration on synchrondrosal cartilage dynamics and the resulting relation of base flexure to facial projection. It was concluded that many features of the Neandertal cranium and face are the byproduct of selection for rapid growth rate. It is also concluded that these effects need not imply species level genetic differences. In fact, tests using least squares and reduced major axis regression imply that early modern Europeans had growth rates intermediate between Neandertals and modern blacks. This result is consistent with Assimilation models and inconsistent with the Total Replacement models.