Sampling Bias in the Trend of Post‐Pleistocene Gracilization: How Terrain Affects Lower Limb Robusticity

Abstract

Many studies have documented a decrease in modern human lower limb measures of cross‐sectional geometry (CSG) throughout the Pleistocene and Holocene. These decreases are often associated with subsistence changes and technology that allowed for a more sedentary lifestyle (e.g., rise of agriculture). Italian Neolithic samples (19‐4 ka) deviate from this trend, with measures similar to earlier, highly mobile populations (Marchi, 2008; Marchi et al., 2011) despite an overall trend for reduced robusticity through Holocene Europe as a whole (Holt et al., 2018). Active populations with a lifetime of mobility on rough terrain have been shown to have higher cortical thickness and CSG properties that resist bending and torsion in the anterior‐posterior plane – which would not fit within the traditional paradigm. Here, we evaluate changes in femoral and tibial midshaft CSG measures of robusticity. These include maximum and minimum second moments of area (Imax/Imin), second moments of area in the x and y plane (Ix/Iy), polar moment of area (J), and cortical area (CA) for populations in Europe, Africa, and Asia (N = 440) throughout the past 40,000 years (Early Upper Paleolithic, Late Upper Paleolithic, Holocene) using ANOVA and linear interaction models. Generally, Early and Late Upper Paleolithic groups show no significant differences, but Early Upper Paleolithic and Holocene groups were significantly different in all femoral measures, and Late Upper Paleolithic and Holocene groups were significantly different in all measures except Ix/Iy. Linear models showed no significant effect of elevation on CSP or any interaction effects except in femoral CA (Early Upper Paleolithic, p = 0.02; Late Upper Paleolithic, p = 0.03; Holocene, p = 0.01). A paradigm of gracilization throughout time is not supported in Asian populations when they are compared within regions. Reduced robusticity in Holocene Andaman Islanders as compared to Japanese/Vietnamese samples suggest that lower limb robusticity can increase because of activities on mountainous terrain, subverting the traditional paradigm. This suggests that we cannot assume that all populations experienced a reduction in robusticity into the Holocene and we must be aware of the danger of a sampling bias in our work.Support or Funding InformationThis research was supported by Sigma Xi, NSF BCS‐0314002, and the American Museum of Natural HistoryThis abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.