Bones are the unsung heroes of biology. Always working beneath the surface, they’re the ossified architecture that makes our bipedal existence possible — not to mention the existence of thousands of other species. And their amazing durability gives archaeologists and paleontologists an unparalleled glimpse into early human history and beyond. Here are seven amazing facts about bones to shine some much-needed light on these building blocks of our bodies.
All animals on Earth fall into one of two categories: vertebrates or invertebrates. This distinction is based on whether an animal has a spinal column. (Those that do, including humans, are the former; those that don’t are the latter.) Although all mammals, reptiles, amphibians, birds, and fish are vertebrates, they’re vastly outnumbered by invertebrates, which include worms, sea sponges, arthropods, and jellyfish (not really fish, despite their name). In fact, of the estimated 1.37 million surviving species on Earth, according to the International Union for the Conservation of Nature, only 66,800 have a spine. It turns out that a backbone is a bit of a biological rarity.
The largest invertebrate group by far is that of the class Insecta, which includes around 900,000 known living species (about 80% of the species on Earth) and millions more that have not yet been described by science. (Some estimates put the number of unnamed insect species as high as 30 million, though it’s likely less than that.) Insects don’t have spinal columns; instead, they have exoskeletons, which, while lacking a backbone, do have some spine-like features. And speaking of spines…
The average human is born with 33 distinct vertebrae, which are connected to one another through flexible joints called facets. Birds, meanwhile, have anywhere from 39 to 63 vertebrae. But even they can’t compete with snakes, especially large species of snakes like pythons. The Australian Oenpelli python (Morelia oenpelliensis), for example, may have as many as 600 vertebrae. That’s nearly three times as many bones as an adult human has in their entire body — though only two times as many as that same human has at birth. Which brings us to the next fact…
Babies pack a lot of bones in their tiny bodies — around 300, in fact, which is nearly 100 more than adult humans have. The reason for this is biologically genius: These extra bones, many of which are made entirely or partly of cartilage, help babies remain flexible in the womb and (most crucially) at birth, making it easier for them to pass through the birth canal. As a baby grows into childhood and eventually early adulthood, the cartilage ossifies while other bones fuse together. This explains the “soft spots” in a baby’s skull, where the bones have yet to fuse completely.
It also explains why kids may be more susceptible to injury — fracture rates are high around the ages of 11 to 15, when many young people experience growth spurts due to puberty. This is because children’s bones have growth plates, which are particularly sensitive to trauma. Those growth plates eventually close as we age, and a child’s bone count decreases until it settles at 206. Our bones continue to change in a process called “bone remodeling” throughout our lives, but the number typically remains stable once we reach adulthood.
Perhaps surprisingly, the lion’s share of those 206 bones in the human body are in our hands and feet. Each foot contains 26 bones, and each hand contains 27, for a grand total of 106 bones in just those four extremities. Interestingly (but perhaps not surprisingly), the hand and foot are similar in terms of bone structure. On our hands, for example, each finger has three bones — the distal, middle, and proximal phalanges — except for the thumb, which has two (just the distal and proximal). Our feet are the same, with three phalanges in each of the smaller toes, and two in the big toe. The five metacarpals — that is, the bones that make up the palm of your hand — are also arranged similarly to the five metatarsals in your foot. The hand, however, has an extra bone called the pisiform, which is located on the outside edge of the wrist and attaches to various tendons and ligaments.
The bones in our hands and feet are relatively small, though not as small as the stapes, the smallest bone in the human body, found in the middle ear. On the other end of the spectrum is the femur, notable for being the longest and strongest bone. The average adult femur — named for the Latin for “thigh,” where it’s located — stretches to about 18 inches in length and can support as much as 30 times the weight of your body. Because of this, it plays a crucial role in our ability to stand and move. It also connects to many muscles, tendons, and ligaments in our hips and knees.
Bones provide necessary skeletal scaffolding, and that means they’re usually connected to other bones via joints woven together with ligaments and tendons. However, there is one notable exception in the human body — one bone that is not connected to any other bone nearby. That exception is the hyoid, a small U-shaped bone in the neck, at the root of the tongue. Instead of connecting to other bones, the hyoid is linked only to muscles, ligaments, and cartilage, making it something of a “free-floating” loner. That’s not to say it’s superfluous, though. The hyoid aids in the very vital human activities of talking, chewing, and swallowing, so it’s actually pretty important.
Your “funny bone,” named as such for its location near the humerus bone — “humorous,” get it? — is not really a bone at all. Rather, it’s part of the ulnar nerve, which runs from your neck all the way to your hand. Nerves are usually protected by bone, muscle, and fat, so they can perform their bioelectrical functions undisturbed, but a small part of the ulnar nerve in the back of the elbow is a little more exposed. There, the nerve is protected only by a tunnel of tissue, known as the cubital tunnel, so when you hit your “funny bone,” the ulnar nerve presses against the medial epicondyle (one of the knobby ends of the humerus bone), which in turn sends a painful sensation throughout your lower arm and hand. And because the nerve gives feeling to the pinky and ring fingers, those two digits may feel particularly sensitive compared to your other three fingers.