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

Abstract

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.

A Craniometric Perspective on the Transition to Agriculture in Europe

“…Hypotheses relating to the nature of the transition to agriculture must contend with two potentially confounding evolutionary processes: non-neutral dispersal (which disrupts neutral gene flow patterns) and potential non-neutral selection in response to changes in subsistence strategy and/or climate (either via phenotypic plasticity or natural selection). The substantial changes in food processing associated with the shift to farming were hypothesized to have a knock-on effect on the relative size and shape of the masticatory apparatus (e.g., Pinhasi et al 2008;Sardi et al 2004b), although most studies of this kind have focused on the foragerϪfarmer transitions in other regions of the world (e.g., Carlson and Van Gerven 1977;González-José et al 2005;Paschetta et al 2010;Sardi et al 2006). Employing craniometric data as a reliable proxy for neutral genetic data is reliant upon the assumption that cranial morphology is evolving neutrally (Brace et al 2006) and, therefore, is not likely to be confounded by selective factors relating to climate, diet, or other environmental forces.…”

“…While the cranium appears to be acting relatively neutrally, and therefore may be used as a proxy for modeling population history analogous to neutral genetic data (Roseman and Weaver 2007;von Cramon-Taubadel and Weaver 2009), global patterns of mandibular variation were shown to be non-neutral (Smith 2011;von Cramon-Taubadel 2011b), correlating instead with differences in subsistence economy between hunter gatherer and agriculturalist populations (see also Carlson et al 1977;González-José et al 2005;Holmes and Ruff 2011;Paschetta et al 2010;Pinhasi et al 2008;Sardi et al 2006). Therefore, the mandible is likely quite phenotypically plastic, remodeling during growth in response to differing dietary (biomechanical) stresses (e.g., Lieberman 2008).…”

The relative correspondence of cranial and genetic distances in papionin taxa and the impact of allometric adjustments

“…In humans, a number of studies have indicated that the morphology of the masticatory apparatus may be influenced by subsistence strategies (Larsen, 1997;González-José et al, 2005;Sardi et al, 2006;Lieberman, 2008;Pinhasi et al, 2008;Paschetta et al, 2010;Holmes and Ruff, 2011;Lieberman, 2011;von Cramon-Taubadel, 2011b). In particular, morphology of the mandible shows a weak correspondence with geographic distance (Nicholson and Harvati, 2006), and a lower correlation with neutral genetic distances than many other cranial regions (Smith, 2009).…”

Bite force estimates and its relationship with characteristics of diet

“…Molleson y colaboradores (1993) y Schmidt (2001), en estudios hechos sobre desgaste dental oclusal han demostrado que la introducción de la cerámica tiene un profundo efecto sobre la dureza de la dieta. Dicho en otras palabras, el incremento en el procesamiento de alimentos que posibilita la incorporación de ítems más blandos a la dieta, habría llevado a una reducción en la actividad masticatoria y como consecuencia, a una tendencia hacia el desarrollo de cráneos de menor tamaño y más gráciles (Carlson, 1976;Carlson y Van Gerven, 1977;Brace et al, 1987Brace et al, , 1991Hannam y Wood, 1989;van Spronsen et al, 1991;Kiliaridis, 1995;Larsen, 1995Larsen, , 1997Lieberman et al, 2004;Sardi et al, 2006;Pinhasi et al, 2008). Esta tendencia debe ser tomada en cuenta con precaución pues Paschetta et al (2010) y Paschetta (2012 demostraron que no siempre las estructuras de mayor tamaño caracterizan a los grupos de dieta dura o rígida y que en general las diferencias de forma son sutiles y se encuentran puntualmente localizadas.…”