human facial features the result of being used as a punching bag? somehow I don’t think so

I saw this story in the newspaper yesterday, & again today on one of the science feeds:

Researchers in the US have studied the skulls of ancient human ancestors and concluded that fist-fighting may have played a role in shaping the male face.

You can read the paper itself here (Carrier & Morgan, 2014). I’m sorry, but to me it reads like a just-so story. Just because modern humans take a swing at each other from time to time, doesn’t mean that this was the case for earlier hominins. The authors of the paper argue that the facial features of robust australopithecines are the result of natural selection acting through bare-fist fighting. However, they don’t offer any actual evidence that this might have happened: nothing on whether paranthropine skulls show the sort of facial damage that you might expect if fighting in this way was sufficiently widespread to act as a selective force. And similarly, no real discussion of whether Paranthropus could form a fist capable of doing such damage. (The paper on Australopithecus sediba to which they refer actually describes sediba‘s hand as a mosaic of features.) In other words, they’re making a sweeping assumption – that paranthropines routinely beat the heck out of each other – to support the a priori assumption that our own facial evolution was shaped by this.

There’s also the question of whether modern human faces show much evidence of having evolved in this way; they actually seem quite prone to damage. Noses & cheekbones are rather susceptible to damage, and the bones of the cranium – thinner than those of Paranthropus – are dangerously easy to break. At the same time, according to the authors’ speculative view, our hands are particularly well adapted to deliver blunt-force trauma.

This quote from the paper (emphasis mine) says it for me; we really are dealing with conjecture & imagination:

Starting with the hand of an arboreal great ape ancestor, it is possible to imagine a number of evolutionary transformations that would have resulted in a club-like structure adapted for fighting.

Rudyard Kipling might have appreciated it – a point also made by Brian Switek in his excellent commentary over at National Geographic.

Carrier, D. & Morgan, M. (2014) Protective buttressing of the hominin face. Biological Reviews doi: 10/1111/brv.12112


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