Humans naturally walk heel-to-toe, just like apes. But lots of mammals—even apex predators, like wolves and lions—don't.

Ever wonder why? A team of researchers from the University of Utah has a new theory: When it comes to brawling, having heels hit the ground gives primates a leg up.

Of course, this is no surprise to anyone who's trained as a boxer, or even spent a little time listening to a boxing coach. Throwing a punch with your feet planted helps you, well, punch harder. But the Utah researchers wanted to understand just how big a role those punches played over thousands and thousands of years as humans evolved.

The theory goes like this: Animals evolve over time to reflect the anatomy they'll need to survive. Smaller primates, like monkeys, walk on their heels to make them faster, more efficient runners. Their limbs are longer, and their tendons and ligaments quickly recover energy. On the other hand, apes and other large animals, like bears, that don't need to be especially fast runners walk heel-down. This is either because it's anatomically beneficial to their fighting success, or their ability to climb and search for food in trees, researchers believe. 

For the sake of comparison, compare an elite boxer (heels planted when he strikes), to an elite long-distance runner (landing on the balls of his feet). "The folks who line up for the Olympic marathon are not built the way the fighters are," said David Carrie, biologist and lead study author, in a press release.

In the study, which was published in Biology Open, researchers set up a force plate for 12 volunteers to stand on while they hit and pushed a large weighted pendulum (think of a heavy punching bag). The volunteers either planted their heels or raised them off the ground, and either stood on one foot or two. Using the force plate, the researchers calculated how much force the participants generated as they hit, pushed, and pulled the bag in different directions.

Their findings? By standing with heels planted on the ground, participants could generate more torque, and therefore hit with more force.

Then, to further prove how that rotational force makes a big difference, volunteers were asked to push the pendulum while standing on a sheet of slippery Teflon while wearing a fuzzy sock. They simply spun in place, unable to generate much force, if any. Hence the scientists' theory: As humans needed to evolve to generate more force with their fists than with their teeth, they learned to sit back on their heels to throw a punch.

Just don't try to fight any bears, okay? No kangaroos, either, except when necessary.