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A selectionist model of phylogenic behaviour is presented in which epigenetic canalization fulfills the pivotal rôle. It is shown that directional selection will result in stress induce creodal destabilization and in genetic unmasking. Both processes will in turn result in a rapid increase in phenotypic variance for natural selection to act on, and hence a sudden increase in the rate of phylogenic change. Acting on the epigenome via internal selection and on phenotypic peripherals via stabilizing selection, natural selection will also assure phenotypic stasis by means of increased genetic concealment, deepened canalization and developmental constraints. The latter two factors allow for the application of a minimax rule of phenotypic change: that part of an organism with the minimum potential for phenotypic change (hence the maximum canalization) will govern the direction of the maximum phenotypic change of the other parts. The hierarchialization of phenotypic change predicted by the minimax rule explains the coexistence of gradualistic and punctuational changes within lineages of the same species.

Fluctuating dental asymmetry was evaluated as an indicator of environmental stress in a group of 202 living Lengua Indians from the Paraguayan Chaco area. Older, less accultured individuals were shown to be significantly more asymmetric than younger individuals who had been increasingly exposed to western foodstuffs and medicine. Lengua Indians demonstrated similar levels of asymmetry to another preliterate group, the Ticuna Indians of Columbia, but were found to be significantly more asymmetric than contemporary caucasoids. Similar patterns of asymmetry in both arcades for males and females were confirmed by analyses of variance and by Spearman's rank-order correlation coefficients. Partitioning variation in the degree of asymmetry by arcade, dimension and tooth revealed significant differences in the effects of tooth and arcade only: asymmetry was greater in the maxilla and greater in the more distal teeth within each morphogenic class.

Static adult intraspecific allometry of jaws and teeth was investigated in a sample of 100 Negro crania. The relations between tooth area, postcanine surface, incisor surface, and four viscerocranial measures were examined separately for males and females. Our results indicate a marked lack of morphological integration between P-sets within the orofacial subregion and a similar lack of correspondence between jaw size and tooth size. Allometric analyses indicate that mandibular length scales negatively allometric to maxilloalveolar length and to bigonial width, that canine base area scales positively to upper and lower jaw length, and that all the other teeth scale negatively to jaw length. The postcanine surface area was found to be negatively allometric to the canine base area, which in turn scaled isometrically to incisor surface. Hence, any lengthening of the mandible will tend to be associated with a relative shortening of the maxilla, with relatively larger canines and a relative reduction of the cheek teeth.

Evaluation of dental casts of 202 living Lengua Indians from Paraguay finds progressive reduction in overjet with age, but no Class III or indication of altered relationship of mandible to cranial base.

The uneven distribution and pattern of staining, revealed on root-planed, periodontally-involved root surfaces by the application of a plaque-disclosing solution, precludes the use of conventional plaque scoring indices or other methods of assessment based on planimetric and gravimetric techniques. A method has been developed and evaluated to quantify stained areas using image analysis. The method is reproducible, with an error factor of 1.32%, and represents a comparatively simple, yet effective technique for quantifying plaque on irregular root surface areas.

The dental crown morphology of 27 Griqua skulls is described and these are compared for microevolutionary consideration. The early Griqua dentitions show a high Khoikhoi/San component and little evidence of Caucasoid or Negroid admixture.

Tooth shape potential resides in those ectomesenchymal cells that colonise the presumptive jaws prior to the commencement of odontogenesis. Support for Butler's field theory as applied to the human dentition hinges on the observation that distal teeth within each morphogenic class are the most variable. This variability, it has been argued, reflects a decrease in the concentration of field substance with increased distance from the polar teeth. In contrast to the above, it is suggested here that tooth size variability should be related to the length of time spent in the soft tissue stage prior to calcification. It is argued that a long soft tissue stage will result in a variable phenotype and vice versa. Odontometric variability of distal teeth is thus unrelated to morphogenetic field concentrations and hence fails to support Butler's field theory.