Genotype, phenotype, and developmental biology of molar tooth characters

Primate molar shapes reflect developmental and ecological processes. Develo pment may constrain as well as facilitate evolution of new tooth shapes, af fecting how reliable dental characters are in phylogenetic studies. Much of the genetic machinery of development uses the same genes among different o rgans, including teeth, limbs, and feathers. Furthermore, within a tooth, t he development of individual cusps repeatedly uses the same set of developm ental genes, forming a "developmental module." The repeated activation of t he developmental module can explain the cumulative variation in later-devel oping cusps. Therefore short, later-developing cusps may be evolvable but a lso more homoplastic. This patterning cascade mode of cusp development can be used to explain the variational properties of dental characters and char acter states related to cusp initiation. The developmental basis and variat ional properties of crown termination, cusp shape, and cusp configuration c haracters are currently less well understood. It is unlikely that there is a simple "gene to phenotype" map for dental characters. Rather, the whole c usp pattern is a product of a dynamic developmental program manifested in t he activation of the developmental modules. Yrbk Phys Anthropol 43:171-190, 2000. (C) 2000 Wiley-Liss, Inc.