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Speaker 1: Welcome to brain Stuff from How Stuff Works, Hey, brain Stuff.

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Speaker 1: Lauren Volgabon here with another classic episode from the How

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Speaker 1: Stuff Works fault. Today's question is one that's seriously bugged

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Speaker 1: me when I was a kid, and it perhaps more

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Speaker 1: tree climbing than I do these days. Why don't humans

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Speaker 1: have tails? Hey, brain stuff? It's Christian Seger. As far

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Speaker 1: as appendages go, tails are pretty much amazing. Over time,

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Speaker 1: different animals have evolved various highly specialized tails. A horse

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Speaker 1: uses its tail to swap flies, for instance, while a

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Speaker 1: bird uses its tail to steer during flight, which leads

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Speaker 1: us to today's question. If these specialized limbs are so useful,

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Speaker 1: why don't humans have them? Why don't people you know me, you,

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Speaker 1: Benedict cumber Patch. Why don't we have tails? Well, there's

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Speaker 1: two answers. First, we don't really need them. In many

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Speaker 1: quadrupedal or four legged creatures like a cat, for example,

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Speaker 1: a tail helps with balance. Fish and marine mammals, on

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Speaker 1: the other hand, use their tails for steering or look emotion.

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Speaker 1: Some lizards and primates use their prehensile tails to grip things,

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Speaker 1: while crocodiles store fatten their tails, kind of similar to

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Speaker 1: the way camels store fat reserves in their humps. But

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Speaker 1: let's look at humans. We're bipedal, meaning we walk on

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Speaker 1: two legs. Our center of gravity passes vertically down our spines,

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Speaker 1: so we don't need a tail to counterbalance the weight

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Speaker 1: of our heads. And unlike some other primates, we don't

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Speaker 1: need a tail to help us hold onto stuff while

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Speaker 1: we swing through trees, because as a species, we don't

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Speaker 1: regularly tarzan our way around the forest anymore. And why

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Speaker 1: have a tail if you don't use it. It's just

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Speaker 1: another thing that takes energy away from the rest of

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Speaker 1: your body. And as our ancestors evolved away from an

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Speaker 1: arboreal lifestyle, a tail just became less and less useful.

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Speaker 1: But here's the second answer. Our ancestors did have tails,

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Speaker 1: and at some point you had a tale too. You

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Speaker 1: can find evidence of our five limbed past in the

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Speaker 1: skeleton of every human being. Each of us has a

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Speaker 1: co six or tailbone, made of fused vertebrate and other primates.

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Speaker 1: This cosix leads to the tail, but again, we don't

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Speaker 1: really need it. It's a vestigial organ. Now I know

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Speaker 1: what you're saying, Come on, Christian, I may not be

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Speaker 1: a doctor, but I'm pretty sure I don't have a tail. Well,

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Speaker 1: maybe not now, but you did while you were in

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Speaker 1: the womb. All mammals have a tail at some point

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Speaker 1: in development. When you were about thirty days old in

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Speaker 1: the womb, you had a tail like structure sprouting out

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Speaker 1: of your body, and if you're like most people, you

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Speaker 1: reabsorbed the structure as you developed. It's extremely rare, but

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Speaker 1: a few modern people have been born with actual tales.

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Speaker 1: This is what's called an atavism, a trait of distant

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Speaker 1: ancestors that reappears in the modern day you. Usually, these

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Speaker 1: tales are just a few centimeters long and often removed

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Speaker 1: shortly after Burton. Today's episode was written by Ben Bolan

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Speaker 1: and produced by Tyler Clang. For more on this and

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Speaker 1: lots of other balanced topics, visit our home planet, how

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Speaker 1: Stuff Works dot com.