Animal Postcranial Evolution (APE) Lab, Skeletal Biology Research Centre, School of Anthropology and Conservation, University of Kent, Canterbury CT2 7NR, UK.
Laboratory for Functional Morphology, Department of Biology, University of Antwerp, Universiteitsplein 1, 2610 Wilrijk, Belgium.
J Exp Biol. 2018 Apr 19;221(Pt 8):jeb170910. doi: 10.1242/jeb.170910.
Evolution of the human hand has undergone a transition from use during locomotion to use primarily for manipulation. Previous comparative morphological and biomechanical studies have focused on potential changes in manipulative abilities during human hand evolution, but few have focused on functional signals for arboreal locomotion. Here, we provide this comparative context though the first analysis of hand loading in captive bonobos during arboreal locomotion. We quantify pressure experienced by the fingers, palm and thumb in bonobos during vertical locomotion, suspension and arboreal knuckle-walking. The results show that pressure experienced by the fingers is significantly higher during knuckle-walking compared with similar pressures experienced by the fingers and palm during suspensory and vertical locomotion. Peak pressure is most often experienced at or around the third digit in all locomotor modes. Pressure quantified for the thumb is either very low or absent, despite the thumb making contact with the substrate during all suspensory and vertical locomotor trials. Unlike chimpanzees, bonobos do not show a rolling pattern of digit contact with the substrate during arboreal knuckle-walking - instead, we found that digits 3 and 4 typically touch down first and digit 5 almost always made contact with the substrate. These results have implications for interpreting extant and fossilized hand morphology; we expect bonobo (and chimpanzee) bony morphology to primarily reflect the biomechanical loading of knuckle-walking, while functional signals for arboreal locomotion in fossil hominins are most likely to appear in the fingers, particularly digit 3, and least likely to appear in the morphology of the thumb.
人类手部的进化经历了从运动中使用到主要用于操作的转变。以前的比较形态学和生物力学研究主要集中在人类手部进化过程中操作能力的潜在变化上，但很少关注用于树栖运动的功能信号。在这里，我们通过对圈养倭黑猩猩在树栖运动中手部受力的首次分析提供了这种比较背景。我们量化了倭黑猩猩在垂直运动、悬挂和树栖指节行走中手指、手掌和拇指所承受的压力。结果表明，与悬挂和垂直运动中手指和手掌所承受的压力相比，指节行走时手指所承受的压力明显更高。在所有运动模式中，压力峰值通常出现在第三指或其附近。尽管拇指在所有悬挂和垂直运动试验中都与基质接触，但拇指所承受的压力要么非常低，要么不存在。与黑猩猩不同，倭黑猩猩在树栖指节行走中不会出现与基质接触的滚动指模式；相反，我们发现第三和第四指通常先着地，而第五指几乎总是与基质接触。这些结果对解释现存和已灭绝的手部形态学具有重要意义；我们预计倭黑猩猩（和黑猩猩）的骨骼形态将主要反映指节行走的生物力学负荷，而树栖运动的功能信号在化石人类中最有可能出现在手指上，特别是第三指，而最不可能出现在拇指形态上。
