[gentle music] - Hey, smart people, Joe here.

Charles Darwin spent five years circling the world to discover what became "The Origin of Species."

Alfred Russell Wallace spent eight years traveling through South Asia to witness the story of evolution.

But you can discover the same thing today without going anywhere.

Because the story of evolution is right there in your body.

Your tailbone used to be a tail.

If you can move your ears, that's thanks to muscles you share with other mammals.

That pink bit in the corner of your eye, a leftover of a third eyelid we can still find in lizards, birds, fish, and others.

Goosebumps are a feature we share with lots of animals that didn't lose their body hair.

[hiccups] And even hiccups trace back to the brains of fish and tadpoles, a brain signal they use to squeeze water through their gills.

These body parts are just a few scattered pages in a larger story about our evolution.

But there's other fossils hidden inside our bodies that tell an even clearer tale about how we came to be the way we are.

[light-hearted piano music] [rocket blasts] One of these stories is so simple, it can be told with a single picture.

These are images of chromosomes, the big chunks of DNA inside every one of our cells.

When we look at images of human chromosomes next to those of other apes, they line up nearly identically, except for human chromosome two.

It seems to have no match next to the other ape chromosomes, even weirder, humans have 46 chromosomes in total, 23 pairs, those other apes, they have 48 chromosomes, 24 pairs.

What could explain this?

If we're supposed to be related, why are we missing a chromosome?

Turns out we aren't missing a chromosome at all.

Some time during our species' history, those two chromosomes that are still separate in other apes were welded to become our single human chromosome two.

Us, chimps, gorillas, orangutans all inherited the DNA we have today from some common ancestor with 48 chromosomes.

But two of ours got stuck together along the way, and you can even see how they match up.

If two chromosomes were glued together, you'd expect to find two centers or centromeres, and we do.

We'd also expect to find telomeres, the ends of each original chromosome stuck head to head in the middle, and we do.

Thanks to sequencing the human genome, we can spot the exact DNA base where this fusion happened.

113,602,928 bases from the end, a fossil of evolution hidden in our own bodies.

[gentle music] In Celtic mythology, there's a place called Tir na nOg, a land of eternal youth.

When one scientist discovered a protein that keeps stem cells forever young, he named it after this place, Nanog.

The human Nanog gene is located on chromosome 12, at least the version of the gene that works.

There are 11 other broken copies of Nanog spread throughout our DNA.

How did these extra copies get spread through our genome like lost socks?

When DNA is replicated, sometimes the same bit gets mistakenly copied twice, and sure enough, we see one broken copy right next to the working Nanog gene, like a messed up DNA photocopy.

We call these broken genes pseudogenes.

And what about those other 10?

There's another way these pseudogenes can spread.

Nanog, like every gene, is copied from DNA into RNA, letter by letter, before that RNA is used to build a protein.

But every once in a very long while, that RNA gets mistakenly copied backwards back into DNA, pasting a new broken version of the gene somewhere in our chromosomes.

After searching the billions of letters in our genome, we found 10 of these lonely Nanog leftovers in our DNA.

Their locations seem random like they were blindly tossed in.

Now, say you were to read another animal's genome, and you found these very same broken copies of Nanog, each pasted in the very same locations among billions of letters of DNA.

That would be a heck of a coincidence, unless it wasn't a coincidence.

This is what we see when we search for Nanog in a chimpanzee's genome.

The original and 10 of those lonely, broken copies, all in the same locations as ours.

This only makes sense if millions of years ago, you and me and the chimpanzee share an ancestor whose DNA was already littered with these broken genes.

We all inherited this pattern because we share an evolutionary link.

Of course, it's one thing to share a link with chimps, but chickens?

That would require some strong clucking proof.

[gentle music] One thing you have in common with a chicken, you both came from an egg.

Inside a chicken egg, the growing embryo produces something called a yolk sac.

It surrounds, well, the yolk, and helps gradually absorb nutrients to build a baby bird.

But human eggs are incredibly small, only about a 1/10 of a millimeter across.

Unlike birds or turtles, our eggs don't make a yolk or even a shell.

We get our nutrients and protection from our mom's body, so you'd think, no yolk, no yolk sac.

But that's not the case.

Humans make an empty yolk sac, and it disappears halfway through pregnancy.

See, this is a clue that our eggs and bird eggs and even reptile eggs all share an evolutionary link.

But can we prove it?

There's an essential ingredient in egg yolks call vitellogenin.

It's a protein, which means there's a gene whose DNA codes how to build it.

Egg-laying vertebrates all have at least one copy of this gene.

But what about us?

If we really are descended from animals that once laid eggs full of yolk, can we find some leftover of that yolky gene hidden in human DNA?

In 2008, researchers found just that.

Fragments of once active egg yolk genes hidden in our own genome.

And when they compared our DNA to the chicken versions, they even had the same neighboring genes around them.

This is exactly what evolution would predict.

Just like fossil bones, we see remnants of our ancestors broken and buried in these hard to find places.

There are many myths of creation around the world, and most agree on one thing.

Humans are special and we need a special story for how we got this way.

When we take a close look at our own biology, we can see that special story is evolution.

And it's a story we share with every other living thing on earth, some more than others.

To some people, the idea that humans, our bodies, our brains, our thoughts are also the products of evolution removes some of the magic of being human, but it doesn't have to.

When Darwin wrote, "There is grandeur in this view of life," he meant that being a creature molded by evolution is a totally different kind of magic, the kind that still amazes you, even when you know exactly how the magic is done.

Stay curious.