Original photo by Pixel-Shot/ Shutterstock
The adult human body contains 206 bones, but that’s just a rough estimate. Biology doesn’t always follow the rules when humans — and other animals — grow from a clump of cells to full-fledged creatures. Even in generally healthy humans, this growing process can create a series of extra, or “supernumerary,” features. This can mean an extra rib, additional teeth, and yes, even an additional vertebra. This last one is particularly notable considering how central the spine is to a healthy, well-functioning body. According to scientists, about 10% of the population has an extra lumbar vertebra (known as L6).
Oops, incorrect!
It's a fibAlthough mammals, lizards, amphibians, birds, and nearly all fish have a spine, vertebrate animals make up only 5% of all species. A large percentage of invertebrate species are insects, which use exoskeletons instead of spines.
Lumbar vertebrae, the largest bones in the spinal column, protect the spinal cord — filled with tissues, cells, and nerves — while supporting the body’s weight and allowing for a wide range of motions. One might think that adding a sixth vertebra to the mix would mess with this delicate biological balancing act, but it turns out that our bodies are smarter than that. According to experts, the L6 vertebra has little to no impact on a person’s health — in fact, most people don’t even know they have one. Sometimes, an extra lumbar vertebra will fuse with the wrong bone, but an arguably greater concern is a doctor or surgeon identifying this extra L6 vertebra as the L5 vertebra, which can lead to medical mistakes known as “wrong-level” surgeries. So while it’s best to know if you’re the rare 1-in-10 case, it’s much more likely than not that your extra spinal bone won’t impact your life at all.
Numbers Don't Lie
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The smallest vertebrae in the spine are known as the ______ vertebrae.
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The smallest vertebrae in the spine are known as the cervical vertebrae.
It’s technically impossible to be “double-jointed.”
Growing up, many people encounter that one friend who seems to be especially flexible — thumbs curve back, limbs jut out at awkward angles, and legs bend with unparalleled pliability. While this contortionist act is often said to be the result of being “double-jointed,” such a medical diagnosis doesn’t actually exist. Instead, a large portion of humanity is best described as having “hypermobility” or “joint laxity.” This means that some people are born with loose ligaments or other bone oddities that make them more flexible than most. For the majority, hyperflexibility isn’t harmful, but a small percentage — those with joint hypermobility syndrome — can experience pain. So in the end, all humans have the same number of joints, but as for the tautness of our ligaments? Well, that’s a different story.
Darren Orf lives in Portland, has a cat, and writes about all things science and climate. You can find his previous work at Popular Mechanics, Inverse, Gizmodo, and Paste, among others.
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