Brain Size, Cranial Morphology, Climate, and Time Machines [and Comments and Reply]

Abstract

A bioclimatic model is evaluated as an explanation of variation in cranial capacity among 122 ethnic groups. Distribution of absolute and relative endocranial volume is mapped. Significant correlations occur with all nine climatic variables examined. Major foci of adaptation occur with solar radiation, vapor pressure, and winter temperature. Global mean trait increase is 2.5 cm per degree of equatorial distance. The interactive geometry between cranial size and shape is described, with encephalization and brachycephalization considered as functionally connected trends. Breadth is the most important structural component determining capacity. Relations between body size and brain size indicate that human populations under severe cold stress obtain large volumes more from rounder cranial shape than from differentiation by total body size. A computerized mapping program is developed and applied to anthropometric, climatic, and HRAF files. Its potential to produce clinal depictions through the Pleistocene ("time machine project") is discussed. Paleontological data are summarized for 147 hominids.