WOMAN: You immediately descend into the mouth of a cave.

WOMAN #2: We suit up.

We put harnesses on.

And we clip into some safety ropes.

And then we're climbing this knife-edge of rock that goes about 20 meters up.

And so if you were to fall off the Dragon's Back, that would be very bad.

WOMAN #1: If any of us was injured on the sort of the far side of the cave, the paramedics would be sent down to us.

And you had to live underground until you could get yourself back out.

You go through that little tunnel, and then you come out, and there was a more open chamber, but we only had our headlamps on at that point.

And so everywhere we looked, you could just see flashes of bone.

[INTRO MUSIC] Hey, smart people.

Joe here.

There may be nearly 8 billion humans on Earth.

But Homo sapiens is a lonely species and not just because we stare at our phones all day, or never go outside, or just watch YouTube videos all the time, because our species is a relict-- the only surviving member of the group of upright apes known as Homo.

But it wasn't always like that.

Walk backwards through time, and you'll see that, at various points, many other human and hominid species walked the Earth, some like us and some very different.

Everything we know about those ancient species stories we know from fossil bones.

And in many cases, that means we don't know very much at all, which is frustrating because we all want to know where we fit in this story.

How did this one species of intelligent ape come to dominate the planet?

And where do we fit in with all the others?

Well, that story just got a whole lot more complicated thanks to a ridiculously awesome bunch of fossils discovered in South Africa over the past several years, which added a new species to the ancient human family.

For the first time ever, these fossils traveled outside South Africa to Dallas, Texas.

So I stopped by the Perot Museum of Nature and Science to check them out and meet the scientists who discovered them and to take a selfie with my ancient cousin.

We'll get to that.

How many people have found new human species, like ever?

Probably a dozen, maybe 15.

And you found two.

Two, yeah sure.

Paleoanthropologist Lee Berger lives and works in South Africa, searching for ancient human fossils.

The scientists have been digging up human fossils in this area for decades.

But thanks to new technology and satellite imagery, in 2013, Lee had identified a few spots he thought others might have missed.

Expert cavers on Lee's team had discovered an unexplored section in what's known as the Rising Star cave system.

They named it the Dinaledi Chamber, meaning "chamber of stars" in one of the local South African languages.

When they descended to the bottom of that chamber, they did find something bright shining back at them-- fossil bones, piles of them.

When Lee saw pictures of the fossils in the chamber, he immediately knew they were fossils of an ancient human relative.

Problem was that he was too big to fit inside the cave to study them.

So he did what any of us would do.

He put out a Facebook post asking for help.

Volunteers needed excellent archaeological, paleontological, and excavation skills.

They must be skinny and preferably small.

And they must not be claustrophobic.

I mean, who wouldn't respond to that?

They were looking for archaeologists with caving and climbing experience.

And before I started studying archeology, I was doing outdoor leadership.

So it sort of sounded like me.

I didn't really expect to hear anything.

But pretty soon, I was underground.

My supervisor sent me the ad and said, "Hey, you have climbing experience.

Don't you have caving experience, too?"

I said, "Well, yes."

And so it sounded bizarre and bizarre enough that I would want to do it.

JOE: Becca Peixotto and Marina Elliott are two members of the six-scientist team who descended into the cave to unearth these fossils and bring them to the surface to study.

Excavating these fossils required what was essentially a military-level operation.

Kilometers' worth of cables were strung so Lee and others in a command tent on the surface could watch every moment of the excavation and communicate with the team underground.

PEIXOTTO: We got dubbed the underground astronauts.

And the people who are on the surface who couldn't come underground with us were watching us on these sort of grainy CCTV cameras.

And it reminded them of watching astronauts working on spacewalks in the space station.

To say that it wasn't easy for them to get to work every day would be a bit of an understatement.

PEIXOTTO: We have to travel through this cave where the narrowest point that we have to get through is 18 centimeters wide.

You have to get down on your belly and sort of do a belly crawl to get through it.

It's called the Superman crawl because folks with broader shoulders have to put one hand over their head, sort of push themselves along with their feet, sort of flying like Superman.

When you come out from under Superman crawl, you can stand up.

And you're in a pretty big chamber.

And that's where the base of the Dragon's Back is.

ELLIOTT: Yeah, and then we end up in an area called the Top of the Chute.

And the chute is actually a long crack or fissure in the dolostone or in the rock.

And it's about 12 meters high.

At its widest, it's only about 45 centimeters.

At its narrowest, it's that 18 centimeters.

JOE: 18 centimeters is like the size of my head.

That's just not-- I have a big head.

[WOMAN LAUGHS] JOE: See if I've got what it takes to join-- join the underground astronaut squad.

Tucking in.

[GROANS] JOE: As they brought the fossils to the surface and began to look at their features, they began to realize they had found something very strange.

For one thing, it was a totally new species.

They named it Homo naledi.

And this wasn't just one individual.

This cave held many individuals, like, plural.

In that first 2013 expedition, we brought up whatever it was, 1,350 fossil fragments, which, in itself, is crazy.

But they all came from a single excavation unit, 80 centimeters by 80 centimeters by 20 centimeters deep.

And we found bones representing-- I think we're up to 22 individuals now.

All of the body parts are represented.

So there's foot bones and hand bones and rib bones and vertebra and teeth and all of it.

The rising star site, the Dinaledi Chamber, the Lesedi Chamber, and other areas around there, we've discovered more individual hominid remains than the entire record of hominid evolution from the continent of Africa.

I think our field had convinced itself there was nothing left to find.

And people stopped looking.

This is a message that there's more out there.

And there's not just a little bit more.

There's a lot more.

OK, now, I don't know how you think fossil hunting works, especially the search for ancient humans.

But that is not how this usually goes.

When people find hominid fossils, you're finding part of a jaw.

You're finding some teeth.

Maybe you're finding just one little digit from a hand.

And that's how species are described.

So there are a whole species that are known from just really small parts of the body whereas, with Homo naledi, we have the whole body from a bunch of different individuals several times over.

Homo naledi's bones don't look like the bones of other ancient humans or hominids.

At least, they don't look like anything we've ever seen together in one single species.

So we're behind the scenes in the Perot Museum.

And we're just going to go in and have a peek at a reconstruction of Neo, so what those bones might have looked like in life.

And this is our buddy, Neo, here.

So Homo naledi has a sort of mosaic of features.

Some aspects of Homo naledi look a lot like our bodies.

And some aspects look a lot like our more ancient relatives.

So they have a really tiny brain, if you can look at the cranium here.

So they have a brain that's roughly the size of an orange.

But when we take endocasts, molds of the inside of the skull, we can see that the brain has a lot of similar features, in terms of the sort of waves and folds on the outside of the brain, as ours do.

So that indicates that while they have a tiny brain, they maybe had a brain that had a lot of functions.

ELLIOTT: So jaws are always cool, in part because everybody knows what their own teeth look like.

And so you can see that Neo's teeth actually don't look that dissimilar from our own.

BERGER: And we've, of course, found complete hands of naledi.

It becomes more and more humanlike.

And so the wrist and hand proportions are almost completely humanlike except for two things.

One, the thumb-- the thumb is utterly unique.

It's extremely long.

And the fingers are curved.

It's curved as the most ancient hominids that we have.

JOE: So that would make sense if this was alive two million years ago.

Absolutely, three million years ago.

But it wasn't.

When we first started looking at the anatomy, I think a lot of people thought, oh, this thing has to be at least a million, maybe two million years old.

Some of the teeth were tested using a technique called electron spin resonance.

So that was one way we were able to figure out that naledi was in this 300,000 years ago range.

ELLIOTT: It really was surprising to find out that naledi was as young as it was.

In the time frame that Homo naledi is, anatomically modern humans were also on the African landscape.

Modern, primitive, and different, all at once.

As of today, the team has recovered fossils from at least 20 individuals from Dinaledi and a nearby chamber.

That brings up a huge question: How did all these bones get in this cave?

Our hypothesis is that Homo naledi were deliberately disposing of their dead.

So we think that Homo naledi's were dying on the surface and their fellows were bringing the dead ones down into this cave system.

We don't know why because we don't have any evidence for that.

And we, unfortunately, can't ask Neo.

He's not too talkative.

[CRICKETS] Deliberate body disposal was one of those behaviors, those rituals, one of the few things that only our species did that made us unique.

And this shatters that idea.

It's another in a long list of things that we used to think of as uniquely part of our species that aren't.

BERGER: Up until Jane Goodall saw chimpanzees actually termite fishing-- boy, that was our gig.

You could look at us and you said, "Wow, we do tools; no one else does tools."

JOE: OK, cross tools off the list.

Yeah, tools, art-- we now know that other animals do complex ornamentation and decoration.

Birds do a great job of that, right?

We know other animals more now.

We know that they grieve over their dead.

They interact with death in a different way.

And many different species do that.

So we've lost that.

And then there's this last thing that we had, this idea of recognition of self mortality, deliberate body disposal, the idea that we deal with our dead.

And the reason that we thought we did that is because we saw ourselves as separate from nature.

We saw ourselves as a creature that was different from other animals.

And therefore, we wouldn't allow any of our individuals to undergo those processes.

If that hypothesis holds here for these specimens in these many different places that we find them now, then you're looking at a creature that shared that.

For me, I often talk about "humans and other animals" because we are animals.

And I think, when we think about ourselves as being part of the animal kingdom, I think that, to me, that helps us bring ourselves back into being co-inhabitants of this planet.

This whole story leads up to some big questions.

Where does Homo naledi fit into our story?

Is it our ancestor?

Is it something else?

Well, the answer isn't simple.

Now, we're all familiar with this version of human evolution, a primitive-looking thing giving rise to a slightly less primitive thing giving rise to another and another and, finally, something like us, something advanced, a march of progress.

Well, that isn't how evolution works.

And Homo naledi is proof of that.

I think this model of the braided stream helps us get over that hurdle of thinking that, you know, one species and then the next generation is born, and it's another species-- but that evolution happens gradually through multiple mechanisms through time.

The idea that we were this inevitable walk to be this.

And humans are this successful dominant thing.

We've hardly been tested yet.

JOE: Yeah, you take air conditioning and delivery food away-- [LAUGHS] --and we're in trouble.

Absolutely.

Thanks to fossils like Homo naledi, we know that the human story played out like a tangled braided stream.

We're at the end of one branch near the end.

But we're not the only branch.

And along the way, back through time, branches have split off to fade out or, perhaps, even join back with others and combine again.

It isn't a tree that grows up in some march towards some ideal best species.

It trickles out simply forward in time, following the landscape carved out by natural selection.

We're just along for the ride, looking back and trying to figure out where we've come from and who our fellow travelers were along the way.

Stay curious.

I want to give a special thanks to the Perot Museum of Nature and Science in Dallas, Texas, for inviting me up to see these fossils in person and meet the scientists.

This is the first and probably the only time these fossils will be outside of South Africa, and I'm just really honored that I got to be next to them and experience this.

They even gave them South African passports.

Are you kidding me?

They'll be on display through early 2020 as part of a exhibit at the museum called "Origins," so if you're watching this before then and you find yourself in Dallas, go check them out.

They aren't paying me to say that.

It's just an awesome thing and you should know about it.

There's links down in the description.

And I'll probably have some more to show you from my visit in a few weeks, so stay tuned.

And thanks to everyone who supports the show on Patreon.

You are awesome, and thanks to you, I get to go see cool stuff like this and share it with everyone.

If you want to join our family, go check out the Patreon page.

We've got a lot of cool perks at different levels, and you can even join the ranks of these Galaxy Brain supporters.

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