In A Nutshell
While your hands developed to be better at manual dexterity, they also evolved, according to one study, to beat things down. When you clench your fist, you actually increase its density by around four times, which allows you to mete out damage without harming yourself too much. Why exactly our hands do this isn’t clearly understood, but researchers think it might have something to do with the fact that, unlike apes, we didn’t need bigger hands to climb trees any more, but still needed to strike things. Chimps hands, incidentally, don’t make a fist when they close but an “open donut shape.”
The Whole Bushel
Compare your thumb to that of the average chimp. Don’t have a chimp around? We pity you. And we can tell you your thumb is slightly longer. This added length is what gives humans the dexterity to create and use tools and is likely a product of the varied length of our toes, which gives you greater balance; hand and foot development depend on some of the same molecules. This only means that when evolution decides to change something about one, it’s likely to change the other.
Okay, so look at your hand again (and, if possible, your chimp companion’s). You’ll notice that your other fingers are shorter than the chimpanzee’s—they have long fingers and a short thumb. We have short fingers and a longer, stronger thumb. Why the disparity? Researchers at the University of Utah suspected it had something to do with the way we make a fist.
Michael Morgan, a student, and biologist David Carrier conducted an experiment involving a whole bunch of martial artists hitting things in various ways and recording the results. First, they discovered that an open slap versus a solid punch did not, in fact, deliver more force overall to a punching bag. However, the second round of experiments, which examined the stability of the fist with and without the thumb against the index and middle fingers, found that the knuckle joint of the index “was four times more rigid when supported by the thumb.” Because the measurement tool the researchers were using was only tracking the index knuckle joint, we can’t say for sure if the other knuckles were similarly strengthened, but it’s likely they were.
The researchers reexamined the thumb’s effect on force again, discovering that the added digit did in fact double the amount of power their martial artists could throw, if you considered how much of a smaller surface area was being struck, but not just because of greater rigidity. In fact, the really awesome power of the thumb, when it comes to punching, is the way it absorbs the impact of a blow and transfers the force through our palms and into our wrists, reducing the chances that we’ll hurt ourselves in a brawl.
So our hands, in short, are designed by nature to be both careful, articulate manipulators, capable of fine art and the wicked guitar solo. But they’re also a couple of staunch bludgeons, ready to go at a moment’s notice (like when your chimp gets you and the gang in a bind.).