Speaker 1: Hey, everybody. As you might be able to tell from
Speaker 1: the podcast, my love of learning didn't stop when I
Speaker 1: finished school, and I imagine since you're listening to the show,
Speaker 1: it's probably the same way. So I want to tell
Speaker 1: you about a new way to learn, the Great Courses
Speaker 1: Plus video learning service. This is a cool service where
Speaker 1: you get unlimited access to thousands of online lectures on
Speaker 1: many topics that are taught by the top professors. And
Speaker 1: I really want you to try this, so we've worked
Speaker 1: it out with the Great Courses Plus, so they're going
Speaker 1: to give our listeners a special chance to watch hundreds
Speaker 1: of their courses for free. And that includes a course
Speaker 1: that I just watched that's called The Inexplicable Universe Unsolved Mysteries. Now,
Speaker 1: this series, Inexplicable Universe is presented by none other than
Speaker 1: astrophysicist Neil Degrass Tyson, and it explores some of the
Speaker 1: universe's biggest mysteries in an engaging and fascinating way. NDT
Speaker 1: talks about black holes, quantum foam string theory, all your
Speaker 1: favorites and I'm a big fan of this and I
Speaker 1: want you to try it too, So, as one of
Speaker 1: our podcast listeners, When you sign up, you will immediately
Speaker 1: get one month free to start any of the lectures
Speaker 1: that you want. So start your free trial today by
Speaker 1: going to the Great Courses plus dot Com slash brain Stuff.
Speaker 1: That's one more time the Great Courses plus dot Com
Speaker 1: slash brain Stuff. Welcome to brain Stuff from How Stuff Works. Hey,
Speaker 1: brain Stuff, it's Christian Seger. As far as appendages go,
Speaker 1: tails are pretty much amazing. Over time, different animals have
Speaker 1: evolved various highly specialized tails. A horse uses its tail
Speaker 1: to swap flies, for instance, while a bird uses its
Speaker 1: tail to steer during flight, which leads us to today's question.
Speaker 1: If these specialized limbs are so useful, why don't humans
Speaker 1: have them? Why don't people you know me, you, Benedict
Speaker 1: cumber Patch, Why don't we have tails? Well there's two answers. First,
Speaker 1: we don't really need them. In many quadrupedal or four
Speaker 1: legged creatures like a cat, for example, a tail helps
Speaker 1: with balance. Fish and marine mammals, on the other hand,
Speaker 1: use their tails for steering or look emotion. Some lizards
Speaker 1: and primates use their prehensile tails to grip things, while
Speaker 1: crocodiles store fatten their tails, kind of similar to the
Speaker 1: way camels store fat reserves in their humps. But let's
Speaker 1: look at humans. We're bipedal, meaning we walk on two legs.
Speaker 1: Our center of gravity passes vertically down our spines, so
Speaker 1: we don't need a tail to counterbalance the weight of
Speaker 1: our heads. And unlike some other primates, we don't need
Speaker 1: a tail to help us hold onto stuff while we
Speaker 1: swing through trees, because as a species, we don't regularly
Speaker 1: tarzan our way around the forest anymore. And why have
Speaker 1: a tail if you don't use it. It's just another
Speaker 1: thing that takes energy away from the rest of your body.
Speaker 1: And as our ancestors evolved away from an arboreal lifestyle,
Speaker 1: a tail just became less and less useful. But here's
Speaker 1: the second answer. Our ancestors did have tails, and at
Speaker 1: some point you had a tale too. You can find
Speaker 1: evidence of our five limbed past in the skeleton of
Speaker 1: every human being. Each of us has a co six
Speaker 1: or tailbone, made of fused vertebrate and other primates. This
Speaker 1: co six 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. Usually, these tails
Speaker 1: are just a few centimeters long and often removed shortly
Speaker 1: after Burton. Check out the brainstuff channel on YouTube, and
Speaker 1: for more on this and thousands of other topics, visit
Speaker 1: how stuff works dot com.