Speaker 1: Welcome to brain Stuff from How Stuff Works, Hey, brain Stuff.
Speaker 1: Lauren Volgabon here with another classic episode from the How
Speaker 1: Stuff Works fault. Today's question is one that's seriously bugged
Speaker 1: me when I was a kid, and it perhaps more
Speaker 1: tree climbing than I do these days. Why don't humans
Speaker 1: have tails? Hey, brain stuff? It's Christian Seger. As far
Speaker 1: as appendages go, tails are pretty much amazing. Over time,
Speaker 1: different animals have evolved various highly specialized tails. A horse
Speaker 1: uses its tail to swap flies, for instance, while a
Speaker 1: bird uses its tail to steer during flight, which leads
Speaker 1: us to today's question. If these specialized limbs are so useful,
Speaker 1: why don't humans have them? Why don't people you know me, you,
Speaker 1: Benedict cumber Patch. Why don't we have tails? Well, there's
Speaker 1: two answers. First, we don't really need them. In many
Speaker 1: quadrupedal or four legged creatures like a cat, for example,
Speaker 1: a tail helps with balance. Fish and marine mammals, on
Speaker 1: the other hand, use their tails for steering or look emotion.
Speaker 1: Some lizards and primates use their prehensile tails to grip things,
Speaker 1: while crocodiles store fatten their tails, kind of similar to
Speaker 1: the way camels store fat reserves in their humps. But
Speaker 1: let's look at humans. We're bipedal, meaning we walk on
Speaker 1: two legs. Our center of gravity passes vertically down our spines,
Speaker 1: so we don't need a tail to counterbalance the weight
Speaker 1: of our heads. And unlike some other primates, we don't
Speaker 1: need a tail to help us hold onto stuff while
Speaker 1: we swing through trees, because as a species, we don't
Speaker 1: regularly tarzan our way around the forest anymore. And why
Speaker 1: have a tail if you don't use it. It's just
Speaker 1: another thing that takes energy away from the rest of
Speaker 1: your body. And as our ancestors evolved away from an
Speaker 1: arboreal lifestyle, a tail just became less and less useful.
Speaker 1: But here's the second answer. Our ancestors did have tails,
Speaker 1: and at some point you had a tale too. You
Speaker 1: can find evidence of our five limbed past in the
Speaker 1: skeleton of every human being. Each of us has a
Speaker 1: co six or tailbone, made of fused vertebrate and other primates.
Speaker 1: This cosix leads to the tail, but again, we don't
Speaker 1: really need it. It's a vestigial organ. Now I know
Speaker 1: what you're saying, Come on, Christian, I may not be
Speaker 1: a doctor, but I'm pretty sure I don't have a tail. Well,
Speaker 1: maybe not now, but you did while you were in
Speaker 1: the womb. All mammals have a tail at some point
Speaker 1: in development. When you were about thirty days old in
Speaker 1: the womb, you had a tail like structure sprouting out
Speaker 1: of your body, and if you're like most people, you
Speaker 1: reabsorbed the structure as you developed. It's extremely rare, but
Speaker 1: a few modern people have been born with actual tales.
Speaker 1: This is what's called an atavism, a trait of distant
Speaker 1: ancestors that reappears in the modern day you. Usually, these
Speaker 1: tales are just a few centimeters long and often removed
Speaker 1: shortly after Burton. Today's episode was written by Ben Bolan
Speaker 1: and produced by Tyler Clang. For more on this and
Speaker 1: lots of other balanced topics, visit our home planet, how
Speaker 1: Stuff Works dot com.