Caton Neil R, Lewis David M G
School of Psychology, University of Queensland, Brisbane, Queensland, Australia.
Division of Psychology, Murdoch University, Melbourne, Western Australia, Australia.
Am J Hum Biol. 2025 Feb;37(2):e70010. doi: 10.1002/ajhb.70010.
Sexual selection via contest competition has equipped countless organisms with weaponry in their appendages to overpower their opponents. Here, we tested (1) whether greater upper limb length-measured as span controlling for biacromial width-confers an advantage in contest competition among adult humans, (2) several possible means by which upper limb length might increase success in intrasexual contest competition, and (3) whether, consistent with male-male contest competition creating stronger selection pressures than female-female contest competition, male Homo sapiens have greater upper limb length.
We collected fight statistics and facial and body photographs from professional combatants (N = 715) in the Ultimate Fighting Championship (UFC; Study 1). Sexual dimorphism in upper limb length was then examined via diverse and demographically representative samples from four studies (total N = 6915), from Croatian adolescents and older Singaporean adults to United States Army personnel born across all major world regions (Studies 2a-2d).
First, we found that greater upper limb length is associated with increased success in intrasexual contest competition, an effect driven by both the capacity to grapple opponents to submission and to knock opponents unconscious (Study 1). Second, we found unequivocal, cross-cultural evidence of unique sexual dimorphism in upper limb length after controlling for allometry: across four studies, men exhibited longer upper limbs than women (Studies 2a-2d).
Upper limb length may have been shaped by intrasexual selection, with implications across the biological, anthropological, and psychological sciences.
通过竞争对抗进行的性选择使无数生物体在其附肢上装备了武器，以战胜对手。在此，我们测试了：（1）以肩峰间宽度校正后的臂展来衡量的上肢长度增加是否会在成年人类的竞争对抗中带来优势；（2）上肢长度可能增加同性竞争对抗成功率的几种可能方式；（3）与雄性间竞争对抗比雌性间竞争对抗产生更强的选择压力一致，男性智人的上肢长度是否更长。
我们收集了终极格斗冠军赛（UFC；研究1）中职业格斗选手（N = 715）的比赛统计数据以及面部和身体照片。然后，通过来自四项研究（总N = 6915）的不同且具有人口统计学代表性的样本，从克罗地亚青少年和新加坡成年老年人到出生于世界所有主要地区的美国陆军人员，研究上肢长度的性别二态性（研究2a - 2d）。
首先，我们发现上肢长度增加与同性竞争对抗成功率的提高相关，这种效应是由将对手缠斗至屈服以及将对手击昏的能力共同驱动的（研究1）。其次，在控制异速生长后，我们发现了明确的、跨文化的上肢长度独特性别二态性证据：在四项研究中，男性的上肢比女性更长（研究2a - 2d）。
上肢长度可能是由同性选择塑造的，这对生物学、人类学和心理学等学科都有影响。
