Chances are you've never even given a second thought as to exactly why it is we, say, cover our mouth when we yawn, or shake hands when we meet someone new. You do it because some grownup told you to, before you were able to comprehend how random and pointless it all is.
Well, it turns out that the origins of the traditions you think of as mundane run the gamut from freaking odd to downright sinister. For example ...
The Tradition You Know:
Somewhere around the time that we outgrow Indian burns and wedgies as our standard social interactions of choice, shaking hands takes over as the common courtesy shown when greeting friends and strangers alike. It's an action so ingrained that we do it with nary a second thought as to where the somewhat moist, unnaturally warm hand that we're reflexively fondling has been. Except for next time. Next time, you're going to think about where that hand's been. You're welcome.
"I just spanked a cow directly in the asshole."
Where It Actually Comes From:
Handshakes are a relic of an era when everyone was a paranoid wreck expecting to be murdered to death by anyone and everyone they saw ... maybe even more so than nowadays.
You see, in the distant past, extending an empty hand was more than a friendly gesture -- it was an indication that a person wasn't holding some sort of sharp rock/knife/wrist-mounted miniature catapult about to be used against you. As history progressed, the practice became more and more complicated to address increasing fears: When ancient Romans got together, for example, they latched onto each other's arms clear up to the elbow to feel for daggers hidden up sleeves.
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It's like Wolverine, but way, way weirder and more inconvenient.
And have you ever noticed that handshakes always involve the right hand? Obviously that's because it's the one most likely to be brandishing a surprise abdomen aerator. At least, that's why some cultures favored the right over the left -- others used the right hand because, in those pre-toilet paper days, your left hand was your ass-wipin' hand.
Medieval Europeans built on the tradition passed down by the Romans, following up the simple arm clasp with a vigorous shake intended to dislodge any particularly well-tucked armaments, which presumably often resulted in a cartoonish pile of impossibly large weapons around the feet of the shakee. Thus what we today know as the handshake was truly born, to remain pretty much unimproved upon until the 20th century invention of hand sanitizer.
"Shit, that was the last of it. Don't introduce anyone to me until after I get back from the store."
The Tradition You Know:
Unless you're British, Australian, or a free-wheeling, high-spirited maniac, you probably drive on the right-hand side of the road. It's one of those things we never really question because it just works, but the truth is that traffic didn't always follow this rule of the road -- in fact, it used to be the exact opposite.
Where It Actually Comes From:
Going all the way back to ancient Rome, inventor of everything, traffic generally stayed to the left. The reason? You never knew what type of sketchy passersby you might run into along the way, and since people lacking mutant superpowers tend to be right-handed, traveling to the left allowed them ample head-cleaving room.
Think about it: If you were passing on the right and went to swing your sword at your newly made acquaintance/enemy on your left, you'd end up stranded in the breakdown lane with a headless horse. So instead you'd stay to the left in order to be better prepared should a fight ensue or if, conversely, friendly fist bumps were offered. The habit of traveling to the left eventually became so ensconced that it was officially codified into law in 1300 by Pope Boniface.
That's an interesting fashion choice for a guy whose name sounds like "boner face."
So how did we end up switching sides? Well, popular legend has it that Napoleon mandated the change because ... he was short, or something? But while it's true that Napoleon (and, um, Hitler) helped spread right-hand road travel, the switch had already in large part taken place before the 19th century -- and once again, it was directly linked to our species' nascent road rage tendencies.
You see, with the introduction of firearms, it no longer made sense for right-handed people to stay to the left, because you'd have to pull some seriously sexy contortions to aim your even sexier arquebus at someone passing you. So instead, travelers kept their guns tucked into their left arms and traveled to the right, thereby being better prepared to fire at someone passing on their left. Take into account that another reason was the poorly designed Conestoga wagon, which forced the driver to sit on the left-rear horse in order to properly yield his whip in his right hand, and it turns out that our tradition of driving on the right came about through a combination of our desires to more easily cap some asses and more efficiently beat our animals.
"When I evolve thumbs, you're all going to pay."
The Traditions You Know:
At some point in human history, it became important for us to be overly concerned with the air intake of other humans. Think about it: When you yawn (which, having just read the word "yawn," you have an overwhelming urge to do right now), you feel irresistibly compelled to cover your mouth, because ever since you were a kid your mom told you that fully exposing your taco tunnel to everyone around you was just not a proper thing to do. And when the goo-flecked air is traveling in the opposite direction in the form of a sneeze, our instinctual reaction is to utter the phrase "God bless you" -- unless said sneeze happens to be aimed directly at your face, to which the societally accepted reaction is to administer a severe beating with the nearest rusty pipe.
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Good girl. You get to live another day. Now, let's work on your farting problem.
Where They Actually Come From:
Early Islamic cultures viewed yawning as an open invitation for Satan to slither his scaly way into your body, presumably to do really evil stuff like use your uvula as a punching bag while tickling your pancreas with his bifurcated tail. Meanwhile, in India, yawning was more of a two-way street: Not only did it allow bhuts (spirits) to enter your body and run amok with their spiritual shenanigans, but it also allowed a little bit of your own soul to escape. Luckily, we humans come equipped with a handy Satan/spirit/soul blocker at the end of each arm. That didn't do much good for infants with their little Jell-O hands, though, which is why early physicians instructed mothers to be constantly attentive to the task of covering their babies' yawns in order to prevent all their soul-stuff from leaking out.
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Which explains why hippos have no souls.
Now let's take an Indiana Jones-style plane jaunt over to medieval Europe, where covering yawns was less spiritual and more of an actual physical necessity. You see, with bubonic plague running rampant across the continent, unlatching your jaw and gulping in a heaping dose of your fellow man's filth was seen as a surefire way to become the next contestant on Watch Your Own Groin Rot Off. During this period, it became common to not only cover your gaping maw during a yawn, but also make the sign of the cross in front of it to ward off the invisible disease gremlins.
Similarly, the custom of saying "God bless you" after someone sneezes also finds its origins in the plague. That's because those who were infected could be identified by a few telltale symptoms, one of which was sneezing -- and since catching the plague was basically an inescapable death sentence, Pope Gregory instructed the populace to start blessing anyone who sneezed. Thus "God bless you" promptly replaced the previous refrain of "Good luck in the afterlife, motherfucker" and, incidentally, anyone with allergies suddenly found themselves with far fewer friends.
That's sign language for "Get the fuck out of my office."