Things You Can(Not) Live Without – Under the Scope

I heard an interesting news story recently. I’d like to say that the story was so interesting it made my ears perk up, but that would be missing the whole point of it. The story was about ear muscles and the idea that humans haven’t used theirs in 25 million years.

Now, humans haven’t been around for 25 million years. What that misleading newsbite really meant is that modern humans have ear muscles like dogs and cats and other mammals that can voluntarily move their ears, but our ear muscles are not fully developed. With keen vision and a great brain to locate things, our prehistoric ancestors didn’t need to move their ears so much. The DNA controlling ear muscle development accumulated mistakes over many millennia, and, because those mistakes caused no harm to individuals, strong ear muscles were not transmitted from parent to offspring over millions of generations. That’s why we’re left today with only a vestige of once useful ear muscles. Wow. You know what? The newsbite sounds better.

To make controlled observations about ear muscles in nature, I engaged a laboratory assistant—my very domesticated cat. I made a hissing sound aloud, expecting to illicit a response. To my surprise, she sat motionless in the distance to the right, and only for a moment her left ear turned slightly in my direction before returning forward. Experiment successful, despite her cool, calm, and collected disregard (until feeding time) for the human with immobile ears.

Ear muscles are one of many body structures in humans that come from our distant ancestry on Earth but that are no longer necessary for modern wellbeing. Sorta like 8-track tapes and cassettes but made of flesh and not plastic. While those tapes became obsolete over a matter of decades, ear muscles and other fleshy structures took much, much longer. We spend much of our lives accumulating stuff like 8-tracks and then try to get rid of it by selling it on eBay and Amazon Marketplace. But biology is slow and has no resale mechanism; instead, its most effective way of getting rid of useless things is to just let them degenerate and fade away across generations. Like ear muscles, we call these apparently useless structures “vestigial.”

The most infamous vestigial structure in humans is the appendix—that little squiggly extension of the lower right turn of the intestines. Sometimes it’s called the “vermiform” appendix because its shaped like a vermin—in this case a worm. Other mammals have appendixes, and that may be associated with their plant-rich diets. In humans, however, an appendix can be surgically removed without affecting life much. So, does the appendix have any benefit in the human world? Most say no, but I disagree: In the course of the six weeks after mine ruptured at age 13, it surely benefitted the finances of my local hospital. So, yes it does have benefit.

Wisdom teeth–that third set of molars in the back of your jaws—are also considered vestigial in modern humans. Like appendixes, wisdom teeth can be surgically removed without affecting life much. They, too, may be a vestige of a plant-rich diet before our ancestors learned to soften veggies over fire or to eat soft dinosaur meat. And they clearly have an economic benefit in the human world—in this case to oral surgeons. In these respects, wisdom teeth and appendixes are quite similar, though, being from opposite ends of the digestive tract, not in an appealing way.

Though my cat did not show a startle response at my hissing, less cool cats would react with their fur raised. This happens when the startled nervous system contracts tiny “arrector pili” muscles across the skin that make hairs stand upright in their follicles. As part of the startle response, it’s believed that such a reaction increases the apparent size of the animal in hopes that its foe will back down from a fight. Compared to furry animals, there’s not much hair on human skin, but if something made “the hair back of your neck stand up” that’s the same sort of startle reaction. Without hair, however, those tiny muscle contractions simply cause “goosebumps.” So, do goosebumps have any benefit in the human world? Most say no, but I disagree: Goosebumps on a selected human are an important nonverbal cue of your impact. Like when you’re dating. Clearly, that’s a useful function in a relatively hairless species.

Speaking of dating, mammals who live in the wild and depend on pheromones to find mates have a concentrated cluster of sensory cells in their nasal passages called the “vomeronasal organ,” which is specialized for ultrasensitive scent detection. Such animals may also have a third eyelid called a “nictitating membrane,” which helps protect and moisten the eye. (“Nictitating” is another word for “winking.”) In humans, with keen vision and a great brain, both the vomeronasal organ and the nictitating membrane are reduced, and most say vestigial. But I disagree: It’s clear that the vomeronasal, the nictitating, and the pili structures work in concert during those precious moments in life when you’re simply looking for that special sign.

Flexing ear muscles are not typically that kind of sign. But there may be other uses. Consider that great Merrie Melodies cartoon called “Malibu Beach Party” with clever caricatures of famous Hollywood stars from the 1940s, like Betty Davis, Bob Hope, and Cary Grant. While all the cartooned stars are relaxing on the beach in Malibu, Clark Gable is out in the gentle surf swimming by backstroke, propelled not by his arms but rather by his true-to-life oversized ears.

But if you’re one of the 90% of humans living today who cannot voluntarily move their ears, don’t despair: There’s probably a lot of other muscles you haven’t used in a very long time.