Is Arm Length a Sexually Selected Trait in Humans? Evidence from Mixed Martial Arts.

Growing evidence suggests that human males have been sexually selected for violent contest competition. I propose the hypothesis that increased arm length is an intrasexually selected adaptation for fighting in males. Longer arms may have provided several advantages to our male ancestors during conflict. However previous research on the effects of arm span on fighting success have shown mixed results and may not have fully accounted for allometric scaling of arm span with size. In a sample of 1,660 modern mixed martial arts fighters, I find that arm span is sexually dimorphic and associated with fighting success, even when controlling for body size. However, effects of arm span on fighting success were very small, suggesting that selection may have been weak. I review evidence for alternative explanations for men's longer arm span and propose future directions to further test this hypothesis.