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To date, differences in craniofacial robusticity among modern and fossil humans have been primarily addressed by analyzing adult individuals; thus, the developmental basis of such differentiation remains poorly understood. This article aims to analyze the ontogenetic development of craniofacial robusticity in human populations from South America. Geometric morphometric methods were used to describe cranial traits in lateral view by using landmarks and semilandmarks. We compare the patterns of variation among populations obtained with subadults and adults to determine whether population-specific differences are evident at early postnatal ontogeny, compare ontogenetic allometric trajectories to ascertain whether changes in the ontogeny of shape contribute to the differentiation of adult morphologies, and estimate the amount of size change that occurs during growth along each population-specific trajectory. The results obtained indicate that the pattern of interpopulation variation in shape and size is already established at the age of 5 years, meaning that processes acting early during ontogeny contribute to the adult variation. The ontogenetic allometric trajectories are not parallel among all samples, suggesting the divergence in the size-related shape changes. Finally, the extension of ontogenetic trajectories also seems to contribute to shape variation observed among adults.

Continuing periosteal apposition (CPA) of small amounts of new lamellar bone, leading to absolutely larger size, has been identified in a number of adult cranial and postcranial bones. This paper reviews 42 studies published since 1964 that have found both significant and nonsignificant age-related change in various skeletal size dimensions, e.g., length, diameter, width, and area. Also considered are four hypotheses that have, or may be, postulated for the occurrence of CPA. To date, however, these hypotheses (cohort effect, mechanical compensation, bone repair and/or mechanical response potential, and heterochrony) have not been rigorously tested, hence remain speculative. An important interpretive problem that befalls the investigation of CPA is its small effect size (i.e., the magnitude of change between observations), since most studies have restricted sample sizes. This problem is illustrated by power analysis of three reviewed studies that reported nonsignificant age-related change. The analysis indicates that these studies had very little likelihood of finding a statistically significant result, i.e., a low probability of rejecting the null hypothesis stipulating no size change with age. This finding has implications for interpreting CPA and for distinguishing between the statistical and biological significance of this phenomenon.

Skull base height increases significantly with better nutrition and health conditions, as seen in comparing 163 nineteenth to twentieth century dissecting-room skeletons (Terry Collection) with 237 modern American middle-class adults (forensic and willed skeletons). The increase parallels the change in pelvic inlet depth index, known to respond sensitively to nutrition, and in stature, and is over six times greater than the general skull size change. Skull base height (porion-basion) is easy to measure with depth gauge and sliding caliper, or by subtraction, and is in adults a sensitive indicator of childhood growth stress.