Welcome back to another episode of Weird Animals!  This week's animal can be found doing all sorts of weird things: running in circles for no reason other than to run . . . walking across a thin rope just to entertain other animals like it . . . and walking down the street holding ice cream.  Yes, this weird animal is . . . a human.  Why do people walk on two feet?  Very few other animals walk this way and they get along just fine.  There must have been something in the past that made their ancestors decide to push back off of their knuckles and awkwardly balance on two legs.  The answer is buried somewhere in history.  We need to travel back in time.  Let's look at some really, REALLY old episodes of Weird Animals . . .  Oh, TV was not invented yet?  We will look at the bones instead then. 


We are going to have to dig deep into our video archives . . . just as archeologists dig deep for bones that will show us everything we need to know about the weird animals of the past.  Let's look for animals that were buried hundreds of millions of years ago.  Not these bones . . .  Not these either . . .  All I can see are giant lizards!  Let's dig around in the dirt to find animals from around 4 million years ago.  Those bones look like a cat with fangs . . .  That looks like a hairy elephant . . .  Where are all the early human bones?  The fossil record is the name for all the different fossils that we've ever found.  We use it to see how people and all the other weird animals on Earth became the way they are.  If we find the right bones, then we can look at how different animals changed over time.  Ah!  Here are some bones from millions of years ago of an animal that kind of looks like a person . . . if a person were hunched over and walking on her knuckles.  She also has much wider hips.  She kind of looks like another weird animal that's still alive today: the ape.  This still does not tell us why people walk on two feet today . . .  Are those bones missing? 

All this fossil wants for Christmas is his two front teeth.


From the past, we have found skeletons that look less hunched over and more like they spent their life walking upright . . .  Here's one!  It's around 4 million year old, and it looks less like an ape with wide hips, and more like the weird guy who lives next door to you.  He's much shorter and has a big forehead, but there is an important difference between him and the apes.  He has smaller hips that let him walk standing up on two feet for a little while at a time!  Bipedalism is a way of walking using two legs.  We have to be able to find many bones of animals between the times of the early apes and today.  We need to find the one animal that came in between.  The animal that decided walking on four legs was for chumps . . . I mean, chimps.   

Look ma, no hands!


Let's keep searching.  Well, now here's something weird.  Many of the skeletons we find look very different.  Millions of years ago and over time we find different animals that look like people.  Some that were taller, some had larger foreheads, but we can't find them walking around today.  This tells us that some of the early apes that turned into people are not living right now and stopped living a long time ago.  Extinction is when the last of a living thing dies and that kind of animal is no longer around on Earth.  The short skeleton with the big forehead is what we call a Neanderthal.  There are none of them buried in the newer parts of the dirt.  This must mean that at least TWO different kinds of animals pushed up off of their knuckles to walk on two feet! 

I feel like I'm the last Neanderthal standing.


So how are we supposed to figure out why weird animals do the weird things they do if we cannot even find the skeletons that started doing it?  The more we dig up bones out of the ground, the more we find skeletons that kind of look like people.  But are they?  Diversity is a lot of different kinds of things.  If you look around your classroom, you will see a lot of people that look different from each other.  This is diversity!  In the Fossil Record we have found a lot of skeletons that look like the people in your classroom that are not people.  Over the last 4 million years, we see different kinds of animals that look even more and more like the people who are around today.  We can now separate these early skeletons into different kinds of skeletons.  Some of them walk on four legs.  Some on two.  Some had big foreheads and are nowhere to be found today.  The people that can be found today showed up a few hundred thousand years ago. 


Well, we set out to find out why people walk on two feet and came up with nothing.  Now we have to dig deep into the earth to search through all the other weird animals to find some answers.  The fossil record shows us the bones of things living in the past.  At some point, this creature stopped walking on four legs and stood up on two.  Some animals that we thought might have been people went extinct, or all of them died out so they are not around anymore.  This leaves us with a very diverse selection of bones, many different choices to search through.  The truth is . . . we don't know why these weird animals that we call people started walking on two feet so they hold ice cream while walking down the sidewalk.  Looks like we'll have to keep digging . . . 


References:

NOVA.  "How Bipedalism Arose"  PBS, 2006.  <http://www.pbs.org/wgbh/nova/evolution/what-evidence-suggests.html>

Encyclopedia Britannica.  "Theories of Bipedalism"  Encyclopedia Britannica, 2009.  <http://www.britannica.com/EBchecked/topic/275670/human-evolution/250597/Theories-of-bipedalism>

Smithsonian.  "Becoming Human: the Evolution of Walking Upright"  Smithsonian, 2012.  <http://www.smithsonianmag.com/science-nature/becoming-human-the-evolution-of-walking-upright-13837658/?no-ist>