Human hands evolved the way they did not so we could use tools but so we could punch each other better, says a new study out of the University of Utah. The lead researcher argues that we could have ended up with any of several different shapes if it were just about holding tools, explains New Scientist. But only one variation would allow us to make a fist and beat the snot out of each other. And that's the one we got. Our fingers are short enough to curl into our palms, unlike other primates, and our glorious opposable thumbs can reach across the fingers to buttress the fist itself for maximum punching power.
The researcher says his theory might explain why high testosterone levels make men's ring fingers longer than their index fingers. That particular combo of finger lengths translates into a better fist, meaning dominant, high-testosterone men would be better fighters. Interesting, says another scientist, but the ability to make a fist was probably a useful secondary effect of hand evolution.