The delicate human hand with its 27 bones folds up into an effective blunt weapon—and that is probably not a coincidence, say researchers who studied the difference between blows from a clenched fist, an unclenched fist, and an open hand. University of Utah researcher David Carrier and his colleagues used fishing line and guitar tuners to string up the arms of nine cadavers for their experiments. The upshot? They say the shape of our hands evolved to make it possible to best punch with a closed fist without damaging bones, especially those in the palm, the Los Angeles Times reports. Most researchers think our hands evolved the way they did entirely because of the more dexterous tasks early humans started performing, but "we suggest that the hand proportions that allow the formation of a fist may tell us something important about our evolutionary history and who we are as a species," Carrier says in a press release.
Carrier, whose earlier research claimed that male faces evolved to take punches, says no other primate can form a "buttressed" fist with the thumb outside the fingers. He admits that his findings are controversial, and notes that a National Geographic science blogger declared his work to be "bro science—dudes pummeling each other driving human evolution." He tells the Washington Post that the idea for the research came during an argument with an old friend about biology, during which his friend held up a fist, and said: "I can hit you in the face with this, but that’s not why it evolved!" (Other researchers claim that people who suffer chronic back pain have less evolved spines.)