Appendix

The appendix, a small pouch attached to the large intestine, is perhaps the best-known useless organ, doing little except occasionally getting infected. However, it turns out that it might not be entirely useless. Scientific theories have been floating around since 2007 that the appendix might actually serve as a “safe house” for beneficial gut bacteria, storing it to replenish it in the rest of the gut if it gets wiped out by illness (or, in modern times, antibiotics).

If this turns out to be accurate, it’s still not a particularly important organ, and if it gets severely infected, you still need to get it removed. Don’t worry: Hundreds of thousands of people get them taken out every year and are doing just fine.

Tailbone (Coccyx)

Humans don’t need tails, but our ancestors sure did — and tailbones, also known as coccyxes, are the last remaining part of them, consisting of three to five vertebrae that aren’t connected to the spine. The coccyx is not a functional tail, but it is woven in with the ligaments, tendons, and muscles in the area. Occasionally, it gets rid of itself by fusing with the sacrum, another lower back bone. In cases of extreme pain that don’t resolve with any other treatment, people can get their coccyx surgically removed, but it’s unnecessary in the vast majority of cases. Occasionally a baby will be born with an actual tail — and human embryos generally form with a tail that later disappears as it grows into the tailbone — but it’s extremely rare.

Wisdom Teeth

Wisdom teeth, a third set of molars, have made dental surgery a rite of passage. For those who get them — many people don’t — they usually start emerging between the ages of 17 and 21. Often, there’s no room in the jaw, and the teeth end up trapped. When that happens, they need to be surgically extracted. Occasionally they grow in without incident and just become extra teeth.

It’s a lot of trouble for a set of teeth that we don’t even need. One theory is that our ancestors, who ate harder-to-chew things and didn’t have dentists, needed them as backup teeth. Modern science has gotten pretty good at just replacing teeth as they fall out, but wisdom teeth could still replace damaged molars in a pinch.

External Ear-Orienting System

If you have a pet dog or cat, you’ve probably noticed their ears snapping to attention at an interesting or startling noise. Humans still have those muscles and, likely, the brain circuits associated with them. In one study, researchers observed tiny, involuntary movements in the directions of interesting sounds. For one part of the study, they had participants read a boring text while they played attention-grabbing sounds like crying babies and footsteps. Next, they had participants try to listen to a podcast while a second podcast played in the background. Those ear muscles fired up in both cases — they’re just obsolete for modern human beings. Some humans can still wiggle their ears, which does serve one purpose: It’s a cool party trick.

Goosebump Muscles

Human ancestors were much furrier than us, and sometimes needed to fluff up their hair for warmth or to look bigger and more fearsome. They had tiny muscles attached to their hair follicles, called arrector pili muscles, that would shift each hair up into a vertical position. Today, in our much more hairless state, those muscles give us goosebumps, also known as goose pimples, when we get chilly, scared, or excited.

Some emerging research suggests these muscles may have a role in combating hair loss — and without them, we wouldn’t have a name for the iconic children’s horror series Goosebumps — but as far as basic survival goes, the arrectores pilorum are pretty much useless.

Third Eyelid

Most animals have a third eyelid, also called the nictitating membrane, which serves as a kind of windshield wiper that distributes tears and clears debris from the eye. This trait evolved out of human beings and some apes, but we still have a tiny vestigial remnant in the inner corners of our eyes. It’s a bit of eye tissue just inside that fleshy pink eye bump. In exceedingly rare cases — only two have ever been reported — humans can have a more developed nictitating membrane that covers a larger portion of the eye.

So why did we lose ours? One theory is that, unlike animals that still have them, we’re not typically sticking our faces directly into bushes or other animals to forage for food, so we have less debris to push out of our eyes.

Palmaris Longus Muscle

The palmaris longus is a muscle stretching the length of our forearm that’s evolving away before our very eyes, literally — because it’s visible when you hold your hand and wrist a certain way, you can actually tell whether you still have yours on sight. It’s already missing in a significant portion of the population, and different studies around the world have observed its disappearance in anywhere between 1.5% and 63.9% of participants.

The muscle helps with wrist flexion in those who still have it, but it’s getting progressively weaker as other muscles take over its duties. If you don’t have one, you can still do all the same things as someone who does have it. While it’s unnecessary as is, the palmaris longus is pretty useful as a donor tendon for plastic surgery.