Protective buttressing of the human hand

From 2012-2014 I worked with Dr. David Carrier investigating the idea that human hand proportions were sculpted at least in part to render our hands as effective weapons. Once hominins became bipedal, our hands were freed from locomotive constraints and were able to evolve in new directions. Our fingers became shorter and our thumbs became longer and more muscular. These hand proportions afforded us great increases in manual dexterity but also allowed our hands to form into buttressed fists, a trait unique among great apes.
We tested this idea by measuring the strain in the metacarpals of cadaver arms when striking a weight in different hand positions. We sutured fishing line to each muscle group of the forearm which then ran to guitar tuners mounted on a plywood board. By turning the tuners, we were able to contract different muscles and shape the hand into any posture desired. The hand then rested on a pendulum which swung forward causing the hand to strike a weight outfitted with an accelerometer. By attaching a strain gauge to the metacarpals, we were able to measure strain and force simultaneously.
We discovered that strain in the bones of the hand was significantly reduced in buttressed punches when compared to an unbuttressed posture (the closest posture to a fist that apes can make) or an open-handed slap. This suggests that our hand proportions do provide some protection when striking with force thereby presenting less risk to the aggressor.
To read more about this study, click here