When a new species evolves, it doesn't just show up fully formed. It takes many, many tiny mutations through many, many generations to gradually change a fin into a leg, for example, or to make a set of gills disappear. Don't believe us? You can find plenty of evidence right on your own body in the form of what are called vestigial traits. Here's a handful of body parts you have that are useless today, but once had a purpose.
The tailbone, or coccyx, is what you have left of the tail your evolutionary ancestors used to help them balance when they lived in the trees. You had a tail once, in fact — we all did. During early development in the womb, the human embryo actually has a tail. The body eventually absorbs it, although in rare cases babies can be born with the tail still intact.
If you've ever wondered why you get goosebumps when you're chilly even though they don't seem to make you any warmer, here's your answer: they're a reflex left over from when your ancestors had fur. Goosebumps are a result of arrector pili, muscles that contract involuntarily when you're cold or experiencing heightened emotions. Those contractions make your body hair stand up straight, and if that body hair was thicker and longer, it could help insulate you or make you look larger to an adversary.
Your ears are plenty useful, sure, but they're also a monument to the many ways our species has changed over the millennia. You know how some people can wiggle their ears? Those people just have slightly more function in the ear muscles we all have, called auricular muscles. Cats, dogs, and primates, to name a few, use theirs to turn their ears like a satellite dish to capture sounds all around them. Humans and chimps just move their heads instead, so they eventually lost the need for these tiny muscles.
Then there are the things that only a handful of human ears have. Some people have a small bump on the rim of their upper ear known as Darwin's tubercle, or sometimes just Darwin's point. It's thought to be a leftover from a joint that helped the top part of the ear swivel down and cover the ear's opening. A minority of people have a tiny hole right where the ear meets the face, too, called the preauricular sinus. Some biologists think that hole could be a vestige from when our ancestors had gills.
Your first set of molars usually come in when you're about six years old, your second set when you're about 12, and your third molars — what people call wisdom teeth — when you reach your twenties. Wisdom teeth can come in in a lot of strange ways: sometimes they come in just fine, other times they get "impacted" or blocked from coming in all the way, and some never come in at all.
Because there are people who have wisdom teeth that work just fine, this one is technically a gray area when it comes to vestigial structures. But those extra molars were definitely more useful for our primate ancestors than they are for us
The appendix is usually the first trait people point to when they talk about vestigial structures, but we have news for those people: scientists think your appendix probably still has a function. It's evolved many, many times in different mammal species, which suggests it's pretty useful. Because its evolution usually comes with immunity-boosting lymph tissue and people who have their appendix removed are more likely to suffer from bacterial infections, all signs point to the likelihood that the appendix does something for your immune system. Just because we don't know why something exists doesn't mean it's useless!!