Department of Biology, Wofford College, 429 N Church Street, Spartanburg, SC 29303, USA
Department of Nutrition and Integrative Physiology, University of Utah, 250 S 1850 E, Salt Lake City, UT 84112, USA.
J Exp Biol. 2020 Jan 23;223(Pt 2):jeb212365. doi: 10.1242/jeb.212365.
Sexual dimorphism often arises from selection on specific musculoskeletal traits that improve male fighting performance. In humans, one common form of fighting includes using the fists as weapons. Here, we tested the hypothesis that selection on male fighting performance has led to the evolution of sexual dimorphism in the musculoskeletal system that powers striking with a fist. We compared male and female arm cranking power output, using it as a proxy for the power production component of striking with a fist. Using backward arm cranking as an unselected control, our results indicate the presence of pronounced male-biased sexual dimorphism in muscle performance for protracting the arm to propel the fist forward. We also compared overhead pulling force between males and females, to test the alternative hypothesis that sexual dimorphism in the upper body of humans is a result of selection on male overhead throwing ability. We found weaker support for this hypothesis, with less pronounced sexual dimorphism in overhead arm pulling force. The results of this study add to a set of recently identified characters indicating that sexual selection on male aggressive performance has played a role in the evolution of the human musculoskeletal system and the evolution of sexual dimorphism in hominins.
性二型性通常源于对特定肌肉骨骼特征的选择，这些特征可以提高雄性的战斗表现。在人类中，一种常见的战斗形式包括使用拳头作为武器。在这里，我们测试了这样一个假设，即对雄性战斗表现的选择导致了用于拳击的肌肉骨骼系统在力量上的性二型性进化。我们比较了男性和女性手臂曲柄的功率输出，将其作为用拳头击打力量产生的指标。使用向后的手臂曲柄作为未选择的控制，我们的结果表明，在将手臂伸展以推动拳头向前的过程中，肌肉性能存在明显的雄性偏性性二型性。我们还比较了男性和女性的头顶拉力，以测试另一个假设，即人类上半身的性二型性是对男性头顶投掷能力选择的结果。我们发现这个假设的支持力度较弱，头顶手臂拉力的性二型性不太明显。这项研究的结果增加了一组最近确定的特征，表明对雄性攻击性表现的性选择在人类肌肉骨骼系统的进化和人属的性二型性进化中发挥了作用。
