About the same time as we stopped hanging from trees and started walking upright, our hands become short and square, with opposable thumbs. These anatomical changes are thought to have evolved for tool manipulation, but David Carrier at the University of Utah in Salt Lake City has an alternative explanation.

He says there are several possible hand shapes that would have allowed greater dexterity, making it less clear why we ended up with the hands we have. But only one hand shape lets us make a fist with a thumb as buttress. …

The athletes could generate more than twice the force with a normal fist as with the thumb-stuck-out fist, because of thumb’s buttressing role. There was no difference in the force they could generate with a normal fist and with an open palm, but Carrier says it’s possible that a fist concentrates the force into a smaller area and so does more damage.