You evolved to get punched in the face, especially if you are a man.

A punch in the face is a universal and direct way of expressing disagreement. It probably precedes any other form of communication, since the proportion of the hand that makes it possible to effectively flex the fingers into a fist already appears in the earliest known hominids, almost coinciding with the onset of bipedalism.

Nowadays, in non-professional fights, the fist as a channel to transmit a message usually impacts on the face of the receiver. In fact, although the bones of the hand can be fractured by a punch, they are strong enough to fracture the bones of the face more frequently. This was probably similar in prehistoric times. In this regard, we know that the genus Australopithecus was already distinguished from chimpanzees, orangutans and gorillas by its wide jaws, which would have provided resistance to twisting and shearing. This robustness was also present in the zygomatic cheek bone and in its frontal process at the outer edge of the eye. Their nasal bones, being less prominent than in modern humans, were also less vulnerable. Subsequently, the development of a flatter face reduced the moment of force of blows to the chin and the new shape of the jaw made it easier for the neck muscles and jaw adductors to limit damage.

Although the mandible and other bones of the skull were developed to counteract the load and stresses during mastication, they seem to be prepared for a much greater load than this. In addition, there are areas that suffer little stress during chewing but are thicker, especially if we take into account sexual dimorphism. In the case of male primates, these thicker areas are the orbital margins, the zygomatic bone and the mandible. On the other hand, the masseter and temporalis muscles can produce more force than necessary in mastication, so it is likely that they protect the jaw during punches, preventing it from dislocating and fracturing. Without going back to another era, we know that the jaw and neck muscles are activated on impact to reduce the risk of a concussion. Even the adductor muscles of the jaw can protect, albeit on a smaller scale. This muscle activity would have allowed the mouth to be kept closed so that the molars, which in Australopithecus had more enamel than in other primates, transferred force from the jaw to the rest of the skull. In contrast, members of the genus Homo had fewer, smaller teeth, weaker muscles and a narrower jaw and cheeks, but also less upper body strength.

In general, although in humans there does not seem to be as marked a sexual dimorphism as in other animal species, males seem to be prepared to hit and be hit, which is in line with their greater presence in violent acts. It is not only size and overall strength that count, but the neck muscles, which can protect bruises, have the greatest difference in strength compared to females. Furthermore, the beard may absorb the force of impact on these vulnerable areas, and it may also reduce friction, although its evaluation in mixed martial arts reveals that it does not appear to be an advantage.

Therefore, it could be assumed that sexual selection has favored those characteristics that allow to withstand a blow to the face. To this we add that the face also became the main area of the body to identify an individual and its characteristics, replacing the buttocks which had a more important role in primates. In this way, it would become clear who could or could not withstand blows to the face.

Sources

• Carrier, D. R., & Morgan, M. H. (2015). Protective buttressing of the hominin face. Biological Reviews, 90(1), 330-346.
• Beseris, E. A., Naleway, S. E., & Carrier, D. R. (2020). Impact protection potential of mammalian hair: Testing the pugilism hypothesis for the evolution of human facial hair. Integrative Organismal Biology, 2(1), obaa005.