Evolutionary changes in the masticatory complex following the transition to farming in the southern Levant.

A post-Pleistocene reduction trend in the dimensions of the masticatory complex followed the transition to agricultural lifestyle in several world regions. A major limitation of previous studies is large temporal gaps between the analyzed skeletal populations, which do not allow the detection and analysis of a diachronic morphological transition. In this work, we analyze a large number of specimens from the southern Levant, where agriculture first emerged in situ and for which there is a good diachronic sequence of the shift from a hunting-gathering way of life to a food producing, farming economy (12,000-7,000 uncalibrated bp). Changes in the masticatory complex are examined in the context of three prevailing dental reduction models: the Probable Mutation Effect (Brace,1963; Brace and Mahler,1971), Increasing Population Density Effect (Macchiarelli and Bondioli,1986) and Selective Compromise Effect (SCE) (Calcagno,1989). A series of linear regressions of dimension vs. time and coefficients of variation for each dimension are analyzed. Our results indicate significant reduction in the buccolingual but not mesiodistal dental dimensions and in the ramus breadth and anterior height dimensions of the mandible but not in its overall size. These findings, taken together with low coefficients of variation for the buccolingual dimensions, suggest selective pressure resulting in reduction of specific dimensions. The observed trend is in partial accordance with the SCE but differs from the trends observed in other regions, and is therefore best explained as a region-specific variant of the SCE.