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slash brain Stuff. Welcome to brain Stuff from How Stuff Works. Hey, brain Stuff, it's Christian Seger. As far as appendages go, tails are pretty much amazing. Over time, different animals have evolved various highly specialized tails. A horse uses its tail to swap flies, for instance, while a bird uses its tail to steer during flight, which leads us to today's question. If these specialized limbs are so useful, why don't humans have them? Why don't people you know me, you, Benedict
cumber Patch, Why don't we have tails? Well there's two answers. First, we don't really need them. In many quadrupedal or four legged creatures like a cat, for example, a tail helps with balance. Fish and marine mammals, on the other hand, use their tails for steering or look emotion. Some lizards and primates use their prehensile tails to grip things, while crocodiles store fatten their tails, kind of similar to the way camels store fat reserves in their humps. But let's
look at humans. We're bipedal, meaning we walk on two legs. Our center of gravity passes vertically down our spines, so we don't need a tail to counterbalance the weight of our heads. And unlike some other primates, we don't need a tail to help us hold onto stuff while we swing through trees, because as a species, we don't regularly tarzan our way around the forest anymore. And why have a tail if you don't use it. It's just another thing that takes energy away from the rest of your body.
And as our ancestors evolved away from an arboreal lifestyle, a tail just became less and less useful. But here's the second answer. Our ancestors did have tails, and at some point you had a tale too. You can find evidence of our five limbed past in the skeleton of every human being. Each of us has a co six or tailbone, made of fused vertebrate and other primates. This co six leads to the tail, but again, we don't
really need it. It's a vestigial organ. Now I know what you're saying, Come on, Christian, I may not be a doctor, but I'm pretty sure I don't have a tail. Well, maybe not now, but you did while you were in the womb. All mammals have a tail at some point in development. When you were about thirty days old in the womb, you had a tail like structure sprouting out of your body, and if you're like most people, you
reabsorbed the structure as you developed. It's extremely rare, but a few modern people have been born with actual tales. This is what's called an atavism, a trait of distant ancestors that reappears in the modern day. Usually, these tails are just a few centimeters long and often removed shortly after Burton. Check out the brainstuff channel on YouTube, and for more on this and thousands of other topics, visit how stuff works dot com.