Decrease of Human Skull Size in the Holocene

Increase in the size of the braincase, so characteristic for human evolution, stopped by the end of Pleistocene. Several authors have noticed a decrease since then, while others at least agree there has been no further increase. Craniometric data collected in a uniform way on 241 series of male crania (approx. 9,500 individuals) and on 101 series of female ones (approx. 3,300 indiv.) originating from the NW quadrant of the Old World (Europe, N. Africa, etc.) and dated from Upper Paleolithic to modem times were used to evaluate the trend. Vault thickness and skull shape were accounted for when calculating cranial capacity (CC) from craniometric data. Among male samples the peak CC occurred in Mesolithic (1593 cc), the lowest value falls in modern times (1436 cc); in female samples timing is the same: Mesolithic maximum of 1502 ccm and modem minimum of 1241 cc. For both males and females the decrease through time is smooth, statistically significant and inversely exponential. A decrease of 157 cc (9.9% of the larger value) in males and of 261 cc (17.4%) in females is a considerable one, of the order of magnitude comparable to the difference between averages for H. erectus and H. sapiens sapiens. Holocene decrease in CC occurs throughout the period of the most significant intellectual achievements. Thus change in brain size can hardly be considered a reliable indicator of cultural change. Since brain size in humans, as in other mammals, is strongly correlated with body size through shared growth regulators, the hypothesis is advanced that the decrease in CC during Holocene is a by-product of a generalized structural reduction known as gracilization of the skeleton. Therefore, the observed decrease in CC may not be a result of the direct operation of selection upon brain morphology