Knuckle sandwich: Did fistfights drive evolution of human face?

Jaws became tough to survive fights, not to eat hard food


Current theory about the shape of the human face just got a big punch in the mouth.

Two University of Utah researchers proposed Monday that the face of the ancestors of modern humans evolved millions of years ago in a way that would limit injuries from punches during fistfights between males.

Their theory, published in the journal Biological Reviews, is presented as an alternative to a long-standing notion that changes in the shape of the face were driven more by diet — the need for a jaw that could chew hard-to-crush foods such as nuts.

“Studies of injuries resulting from fights show that when modern humans fight, the face is the primary target,” biologist David Carrier said. “The bones of the face that suffer the highest rates of fracture from fights are the bones that show the greatest increase in robusticity during the evolution of early bipedal apes, the australopiths.”

These are also the bones that show the greatest difference between women and men in early human ancestors and modern humans, Carrier added.

In both apes and humans, males are much more violent than females, and most male violence is directed at other males, Carrier said. The violence underpinning the need for a more robust facial structure may have involved fistfights over females, resources and other disputes.

Australopithecus was a lineage that preceded our genus, Homo, and it emerged more than 4 million years ago in Africa. Australopithecus was bipedal, smaller than modern people and possessed a combination of ape and human characteristics.

“Comparing great apes such as chimps and gorillas to australopiths, what changed in the face was a reduction in the length of the jaws, a great increase in the robustness and strength of the jaws, molar teeth and jaw muscles, a substantial increase in the size and strength of the cheek bones, and an increase in the part of the face that surrounds the eyes,” Carrier said.

The proportions of the hand that allowed for the formation of a fist and the great increases in the robustness of the face occurred early in our lineage, 4 million to 5 million years ago, at about the same time bipedal posture appeared, Carrier added.

Carrier said anthropologists have thought the new facial traits in the first bipedal apes were the result of a diet that included very hard objects, and the biomechanics of eating such food can explain many of these features. But he said recent analyses of wear patterns in teeth suggest most of these creatures did not eat hard objects.

The study by Carrier and Michael Morgan, a University of Utah physician, builds on their previous research highlighting the role they contend violence played in human evolution.

“I think our science is sound and fills some long-standing gaps in the existing theories of why the musculoskeletal structures of our faces developed the way they did,” Morgan added.

  • safetynet2razorwire

    Many hypotheses try to mate with scientific queries – few leave genes behind.

    Those that fail (as review and consideration of the principals’ previous musings suggest these conjectures will do) still contribute by challenging all the other postulates to defend their interpretation of the data amassed to date.

    It’s vital evolutionary scientists erase from their world-view concepts antithetical to the realities of evolution by natural selection. Concepts corrupted by mythic ideas related to ‘meaning’, ‘purpose’, ‘intent’ as in evidence in this our physical universe.

    In other words they must expunge the illusory sense that what has come to be has arrived here and now by any sort of path. The trail behind us – the dotted line our footsteps sketch between ‘origins’ and the current state of evolutionary process – was not there when we set out. We (life) did not follow a marked path but cut our own in our dogged determination to put distance between ourselves and danger/ predation; and to draw nearer to succor/nurture.

    The authors’ attempt to reverse-engineer several traits and features common to many modern humans (but so far from general as to be of questionable validity) and ascribe a single element of the behavioral environment a causative role in shaping of anatomy (hand and lower front quadrant of the skull) and of behavior (intra-species male violence). The hypothesis devolves to mere conjecture soon after arriving at what should have been its starting point: the beings who lived in the time and place when and where hominines became distinct from hominoids.

    This would have required the authors to build a detailed evolutionary context – and should have given them pause about offering their work for peer review. It would have had them striving to dismiss their premise and explore the facts in evidence – beginning with those pre-hominids – and with the modern primates most physiologically (anatomically and functionally) like them. Beginning before we parted company in the woods – with the last direct common ancestor of both hominins (Austalopithecus to us) and the other hominines (pan paniscus, pan troglodytes, and gorillas). From there exploration would proceed to comparison of early hominid anatomy and behavior with the behavior of pan p., pan t., and gorillas. While hominid study relies entirely on the fossil record, primate study possesses a respectable and growing body of understandings among a mass of accumulated raw data – drawn from both in situ (natural setting) study as well as captive (laboratory) study.

    DNA data confirms that the only reason human beings class ourselves (homo) apart from bonobos and chimpanzees is ego. We are genetically so close were we any other animal we’d automatically class ourselves together with the pans.
    We are, genetically, pan sapiens – or they homo paniscus or homo troglodytes.

    Intriguingly, separated by the 2 million year wide raging Congo River, pan p. and pan t., while evolving with typical physiological evolutionary slowness have, like ourselves become culturally distinct. Bonobos are inherently hedonic and live a remarkably egalitarian existence; chimpanzees agonic and (pathologically so) hierarchical; and humans appear to, in general, bifurcate along gender lines – with strongly hedonic ‘feminine’ and a strongly agonic ‘masculine’ sub-cultures.

    Knowing what we already do about the role of sexual politics in the societies of relatives so close there’s no physiological/genetic reason we can’t cross-breed we can reasonably consider their cultural evolution relevant when studying our own. And the relationship between their physiological profiles and ours when we seek to understand who we are and how we arrived here (and even where we’ll go from here).

    Chimpanzees are, apparently, adrenaline ‘junkies’ – adrenaline, testosterone, and their impact on serotonin levels shaping the character, attitudes and the behavior of chimpanzee individuals and their communities (‘alpha’ males have the highest serotonin levels – as long as they remain in charge of the troupe).
    Their social order is hierarchic – the hierarchy requiring continual maintenance
    – in the form of combativeness.

    Bonobos are, apparently, dopamine ‘junkies’ – oxytocin, estrogen, and their relationship with serotonin levels shaping the character, attitudes, and behavior of bonobo individuals and communities (‘alpha’ females have the highest levels of oxytocin – but, unlike the influence of the psychoneuroendocrine variants on the non- alpha chimpanzee community, the entire community shares enhanced empowerment through elevated immunoreactive serum oxytocin.

    To put it bluntly: chimps determine and maintain social order via pain and fear; and bonobos determine and maintain social order via pleasure.

    Chimpanzees are ‘fighters’. Bonobos are ‘lovers’. Most humans appear to be lovers rather than fighters (despite the horrific impact of those pathologically predisposed to conflict on cultural homeostasis.

    Which brings us to a beginning – one with living exemplars against which to test our premises about both physiological and social evolution.

    Just a suggestion.