Department of Anatomy, Arizona College of Osteopathic Medicine, Midwestern University, 19555 N. 59th Ave., Glendale, AZ 85308, USA.
Department of Medical Sciences, Frank H. Netter MD School of Medicine, Quinnipiac University, 275 Mt. Carmel Ave., Hamden, CT 06518, USA.
J Hum Evol. 2018 Jun;119:64-82. doi: 10.1016/j.jhevol.2018.03.003. Epub 2018 Apr 11.
The systemic robusticity hypothesis links the thickness of cortical bone in both the cranium and limb bones. This hypothesis posits that thick cortical bone is in part a systemic response to circulating hormones, such as growth hormone and thyroid hormone, possibly related to physical activity or cold climates. Although this hypothesis has gained popular traction, only rarely has robusticity of the cranium and postcranial skeleton been considered jointly. We acquired computed tomographic scans from associated crania, femora and humeri from single individuals representing 11 populations in Africa and North America (n = 228). Cortical thickness in the parietal, frontal and occipital bones and cortical bone area in limb bone diaphyses were analyzed using correlation, multiple regression and general linear models to test the hypothesis. Absolute thickness values from the crania were not correlated with cortical bone area of the femur or humerus, which is at odds with the systemic robusticity hypothesis. However, measures of cortical bone scaled by total vault thickness and limb cross-sectional area were positively correlated between the cranium and postcranium. When accounting for a range of potential confounding variables, including sex, age and body mass, variation in relative postcranial cortical bone area explained ∼20% of variation in the proportion of cortical cranial bone thickness. While these findings provide limited support for the systemic robusticity hypothesis, cranial cortical thickness did not track climate or physical activity across populations. Thus, some of the variation in cranial cortical bone thickness in modern humans is attributable to systemic effects, but the driving force behind this effect remains obscure. Moreover, neither absolute nor proportional measures of cranial cortical bone thickness are positively correlated with total cranial bone thickness, complicating the extrapolation of these findings to extinct species where only cranial vault thickness has been measured.
系统强壮性假说将颅骨和肢骨的皮质骨厚度联系起来。该假说假设，厚皮质骨部分是对循环激素（如生长激素和甲状腺激素）的全身性反应，可能与身体活动或寒冷气候有关。尽管这一假说已广为人知，但颅骨和后躯骨骼的强壮性很少被同时考虑。我们从非洲和北美的 11 个人群中获得了来自单个个体的相关颅骨、股骨和肱骨的计算机断层扫描（n=228）。使用相关、多元回归和广义线性模型分析颅骨顶骨、额骨和枕骨的皮质厚度和肢骨骨干的皮质骨面积，以检验该假说。颅骨的绝对厚度值与股骨或肱骨的皮质骨面积没有相关性，这与系统强壮性假说不一致。然而，颅骨和后躯之间的颅顶总厚度和肢体横截面积标准化的皮质骨测量值呈正相关。在考虑了一系列潜在的混杂变量，包括性别、年龄和体重后，后躯相对皮质骨面积的变化解释了颅骨皮质骨厚度比例变化的约 20%。尽管这些发现为系统强壮性假说提供了有限的支持，但颅骨皮质厚度并未在人群中随气候或身体活动而变化。因此，现代人类颅骨皮质骨厚度的一些变化归因于系统性影响，但这种影响的驱动力仍不清楚。此外，颅骨皮质骨厚度的绝对和相对测量值均与总颅骨厚度没有正相关，这使得这些发现难以外推到仅测量了颅顶厚度的灭绝物种。
