Bowland Lucyna A, Eason Lesley H, Delezene Lucas K, Plavcan J Michael
Department of Anatomy, Arkansas Colleges of Health Education, Fort Smith, Arkansas, USA.
Department of Anthropology, University of Arkansas, Fayetteville, Arkansas, USA.
Am J Biol Anthropol. 2025 Mar;186(3):e70018. doi: 10.1002/ajpa.70018.
Humans display species-wide right-hand preference across tasks, but this pattern has not been observed at comparable levels in nonhuman primates, suggesting the behavior arose after the panin-hominin split. Muscle attachment sites (entheses) are used to infer soft tissue anatomy and reconstruct behaviors within skeletal populations, but whether entheseal size asymmetry can reflect hand preference remains unclear. If entheseal asymmetry is linked to hand preference, we expect to see greater asymmetry in human hands, where hand preference is more pronounced, compared to nonhuman primates. We tested for bilateral asymmetry in the size of the opponens pollicis muscle flange using a sample of humans and catarrhine primates to determine if enthesis development can be a reliable indicator of hand preference.
We assess the asymmetry of the opponens pollicis enthesis between paired (left/right) first metacarpals using distance-based heat maps generated from three-dimensional models of Homo sapiens (n = 85 individuals), Macaca fascicularis (n = 58 individuals), Gorilla spp. (n = 8 individuals), and Hylobates lar (n = 44 individuals). Metacarpals were cropped to isolate the metacarpal shaft and capture the majority of the enthesis while eliminating variation from the metacarpal ends.
We found right-directional asymmetry for humans; no significant differences are observed for Hylobates, Macaca, and Gorilla.
The opponens pollicis enthesis shows right/left hand bias in humans. The lack of significant asymmetry in nonhuman primates suggests entheseal development in these species does not reflect the same level of hand preference observed in humans. Nonhuman primates can serve as a baseline for studying enthesis asymmetry based on the size of the opponens pollicis enthesis.
人类在各种任务中都表现出全物种的右手偏好，但在非人类灵长类动物中尚未观察到类似程度的这种模式，这表明这种行为是在泛猿 - 人亚科分化之后出现的。肌肉附着点（起止点）被用于推断软组织解剖结构并重建骨骼群体中的行为，但起止点大小不对称是否能反映手偏好仍不清楚。如果起止点不对称与手偏好相关，那么我们预期与非人类灵长类动物相比，在人类中手偏好更为明显的情况下，手部的不对称性会更大。我们使用人类和狭鼻猴类灵长类动物样本测试了拇对掌肌凸缘大小的双侧不对称性，以确定起止点发育是否可以作为手偏好的可靠指标。
我们使用基于距离的热图评估配对的（左/右）第一掌骨之间拇对掌肌起止点的不对称性，这些热图由智人（n = 85 个体）、食蟹猴（n = 58 个体）、大猩猩属（n = 8 个体）和白掌长臂猿（n = 44 个体）的三维模型生成。掌骨被裁剪以分离掌骨干并捕捉大部分起止点，同时消除掌骨末端的变异。
我们发现人类存在右向不对称；在白掌长臂猿、食蟹猴和大猩猩中未观察到显著差异。
拇对掌肌起止点在人类中显示出右手/左手偏向。非人类灵长类动物中缺乏显著的不对称性表明这些物种的起止点发育并未反映出在人类中观察到的相同程度的手偏好。基于拇对掌肌起止点的大小，非人类灵长类动物可作为研究起止点不对称性的基线。
