A rather ‘interesting’ new paper in Biological Reviews claims that:

‘Hands evolved to punch faces. Faces evolved to take punches. That’s the hypothesis being bandied about by University of Utah researchers Michael Morgan and David Carrier, the pair proposing that the apparent “protective buttressing” of our skulls and hands is a sign of violent prehistoric fights where fists of fury dictated who would mate and who would exit the gene pool.’

Nice critique of the paper can be found here: http://phenomena.nationalgeographic.com/2014/06/10/our-skulls-didnt-evolve-to-be-punched/

And the original paper here: http://onlinelibrary.wiley.com/doi/10.1111/brv.12112/full