| Description |
Our study investigated selective mechanisms that influenced the evolution of facial hair in human males (Homo sapiens). Beards are often perceived as an indicator of masculinity and social dominance in men, suggesting that they may play a role in male contest competition. Some authors propose that the beard has a function similar to that of a lion's mane, serving to protect vital areas like the throat and jaw from lethal attacks. This is consistent with the observation that the mandible, which is superficially covered by the beard, is one of the most commonly fractured facial bones in interpersonal violence. We hypothesized that tissues covered by hair would disperse the force of a blunt impact more effectively than tissues without hair. We tested this hypothesis using a Drop Weight Impact Tester affixed with a load cell to collect force versus time data, and modeled human tissue using a short fiber epoxy composite as a bone analogue and skin from domestic sheep (Ovis aries). Tissue samples were prepared in three conditions: hairy (n=20), plucked (n=20), and sheared (n=20). Our analyses found significant differences between hairy and plucked samples for peak force (15.60%), peak energy (36.77%), time to peak force (61.17%), and time to peak energy (77.04%). The same was true of the hairy and the sheared samples for peak force (12.79%), peak energy (31.24%), time to peak force (47.10%), and time to peak energy (63.14%). Hairy samples were capable of absorbing more energy than hairless samples, by distributing the force of impact over a larger time frame, resulting in less instantaneous force applied to the sample at any given time. These data support our hypothesis, and may support the argument that human beards may have evolved to protect vulnerable regions of the facial skeleton from damaging strikes. |
