Practice English Speaking&Listening with: CARTA Presents The Origins of Today's Humans - John Hawks, How Homo Naledi Matters to Our Origins

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- We are the paradoxical ape.

Bipedal, naked, large-brained.

Long, the master of fire, tools and language.

But still trying to understand ourselves.

Aware that death is inevitable, yet filled with optimism;

we grow up slowly.

We hand down knowledge.

We empathize and deceive.

We shape the future

from our shared understanding of the past.

CARTA brings together experts from diverse disciplines

to exchange insights on who we are and how we got here.

An exploration made possible by the generosity

of humans like you.

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- I'd like to take you all with me to South Africa,

where today, above the Rising Star Cave system,

it looks very much like this.

It's beautiful weather there right now.

In 2013, Rick Hunter and Steven Tucker went underground

at this site, looking for bones.

And what I'm gonna show you is the video that they took,

going for the first time into

a previously unknown cave chambers

that we call the Dinaledi chamber.

This is Steven Tucker descending down a very narrow squeeze

that we call the chute.

It's a 12 meter, vertical descent.

And you see here at the base,

bones exposed on the floor of the cave chamber.

This partial skull that you saw there in that video.

This mandible, that clearly from the photographs

that they brought out of the cave, looked like

a hominin mandible, not a modern human.

It was interesting enough for my friend, Lee Berger,

at the University of Witwatersrand,

to organize an expedition,

to see what these bones were, to recover them,

to bring them out of the cave, to study them,

and to try to understand them.

It looked to us like there might be

a large part of a hominin skeleton,

in the bones we saw on the surface.

And that was big news but this posed a big challenge.

Because the Rising Star Cave system has a number

of very narrow constraints in it

that make it very difficult to pass.

And in particular, the one above the chamber

with the bones, called the chute,

is a 12 meter, vertical drop that has a minimum width

of seven and a half inches or 18 centimeters.

It was gonna take some extraordinary scientists

to get through this and Lee, on a Facebook call,

found some extraordinary archeologists who were capable,

not only of the underground skills and the climbing skills

necessary to get into this cave chamber,

but also the excavation skills necessary

to recover and document the bones there.

One of these people, Lindsey Hunter, second from the right,

is a staff member here at CARTA, now, she's in the room.

Several of the others have worked with us

continuously since 2013, in various aspects of the project.

Becca Pichardo at the Perot Museum of Nature and Science

in Dallas right now, is curating the first exhibition

of the Homo naledi material, in the United States.

Aliya Gustaf, Ellen Foy Regal, Marina Elliot,

who's for a long time coordinated all excavation work

in Rising Star, and on the very right, Hannah Morris.

This work is done by a team of more than

a hundred collaborators around the world.

And I'm gonna try to share some

of the big picture aspects of it.

I want you to know that this work is not possible

without the tremendous collaboration

and wholehearted helpfulness and just spirit for the work,

both in the field underground and also

in the laboratory of these extraordinary people.

I'll point out many of them,

some of them are here in the room with us.

So, in November of 2013,

the expedition spent 28 days underground,

recovering fossil remains in the chamber.

What looked to us from the surface like possibly

the remains of one skeleton, turned out to represent

the remains of many, many individuals.

And you see here the excavators, Marina and Hannah, working

on a bone bed that we exposed very rapidly.

All of our work during the first couple of field seasons

were dedicated to excavating approximately

20 centimeters of depth in an area of about

80 centimeters on a side.

In that area, we recovered more than 1500 hominin specimens,

representing a minimum of 15 individuals.

A study of these specimens in the laboratory convinced us

that over the course of a couple of years

that we were looking at something

that we'd never seen before in the hominin record.

This was a new species,

not like other hominins that we'd found so far.

And our team named the new species, Homo naledi.

I'll give you a brief tour of what Homo naledi is like.

It's different from us in many respects and yet similar.

Its hands for example, have fingertips that are broad,

which are great for exerting a grip through the fingertips.

It has wrist bones that are configured

more like modern humans and Neanderthals

and other earlier hominins,

but its fingers are also very curved in its bones,

which suggests that it was using them on a curved substrate

while it developed, and that suggests

that climbing was very important its behavior.

Its feet are mostly modern human-like;

in their proportions, in the presence of a longitudinal

and transverse arch.

And yet, the lateral toes are a little bit longer,

on average, than ours

and the arch is a little bit flatter than ours.

Its brain, between 450 and 600 cubic centimeters

in the specimens that we've recovered,

is around a third the size of modern human brains.

This is similar to earlier hominins, like Australopithecus

and not very much like most other members of the genus Homo.

Across its skeleton, it exhibits a mosaic of traits,

some of them very much like modern people,

and some of them, very much like very early hominins

and not very much like us.

Its shoulders are configured

to be reaching upwards very easily,

that seems like a climbing feature.

Yet its legs are very long

and look like they're really well made for striding.

Its pelvis is a little bit flattened and more flaring,

similar to some of the earliest hominin pelvis, like Lucy's.

And yet, its hands and its jaws resemble

the Argenis in most respects.

Its teeth are human like in size,

and yet they're very primitive in their anatomy.

It's an odd combination.

I wanted to put this slide up here to remind me

to tell you that we've recovered the remains

of individuals of all ages.

From neonates, through toddler age individuals, young

and older children, through young and older adults.

The distribution of ages in the sample

that we have now, which is stretching up to around

25 individuals in the cave system,

is very much like Neanderthals and early homo

in terms of not very much representation of older adults.

But uniquely, we have a very high representation

of children in the site

and that gives us some important insights

into the development of this species.

Including the fact that it's dental development appears

to have progressed in a human life pattern,

not very much like earlier hominins

and other non-human primates.

Early canine development relative to the molar eruption,

and so it's a very unique combination of things.

Our team didn't stop exploring in the cave system in 2013.

Rick Hunter and Steven Tucker rapidly identified

a second cave chamber in the system

that had hominin material.

Over the course of three years, our team,

led by Marina Elliot, recovered material

from that second chamber, the Lesedi chamber,

which is 130 meters through the cave system

from the first, the Dinaledi chamber.

It's very clear that these hominins

were using large parts of this underground system

and we're quite familiar with it.

In the Lesedi chamber, we recovered the

really impressive skeleton of an individual

of Homo naledi, which we named Neo.

In addition to parts of at least two additional individuals.

And so, we have an extraordinary situation

where multiple parts of the cave system

are representing a previously unknown hominin

in a situation that we'd never found them before,

in the continent of Africa.

Our work to date the site took some time.

Eventually, we were able to sample directly

from the Homo naledi teeth themselves,

in addition to geological samples in the Dinaledi chamber

to narrow down the range of dates

for this hominin fossils sample

between 236,000 and 335,000 years ago.

For a hominin that has a brain, a third the size of ours,

in Africa, this was very surprising to us.

It means that Homo naledi was there at the same time

as our immediate ancestors, early humans,

early modern Homo sapiens.

No one guessed that we had to share the continent of Africa

with something that was not very much like us

at the same time that our species was originating.

That raises many interesting questions.

And I'm here to tell you today,

that I'm gonna discuss some of these questions.

And they're questions that I do not have the answers to.

I have a lot of information that's interesting

with respect to these questions.

And that makes me think very hard about some of them.

And that wakes me up at night sometimes,

and certainly wakes up my collaborators,

if I'm not the one waking them up saying,

"Why isn't this done yet?"

So, you've got these great questions,

and I'm gonna review some of them.

The first and most obvious one is,

if Homo naledi is there 250,000 years ago or so,

and it's got hands that look like they're

really well suited to making tools,

what kinds of artifacts are associated with it?

Are they making the same kinds of artifacts

as Homo sapiens, at the same time?

Now, when we talk about the Middle Stone Age in Africa,

which is this time period,

in terms of the archaeological record,

oftentimes people think about later aspects

of the Middle Stone Age.

Famous things like the geometrically-incised designs

on this block from Blombos cave.

Things like the great diversification across Africa

of different point styles.

This is an a figure from Sally McBrearty and Alison Brooks

and Alison's here in the audience with us.

This is a famous thing about the Middle Stone Age

that you have this regional diversification.

It is only relatively recently

that we've developed some more insight

about the earlier phases of the Middle Stone Age,

as as the Levallois manufacturing technique

is really starting to take over from large cutting tools

in earlier traditions.

These are the Jebel Irhoud tools, which we saw earlier today

in Professor Blonde's talk.

They're from Morocco and this is a really unique case

in Africa, where we have a very early Middle Stone Age

that's associated with skeletal material

of a hominin, in a stratigraphic layer.

So, we know that they're the same time.

They seems like they're probably associated with each other.

There are almost no fossil associations

for other Middle Stone Age,

earlier Middle Stone Age assemblages

throughout the continent.

For example, these hafted points from Kathu Pan

in South Africa, are among the earliest known

in the African continent, before 400,000 years old.

Who made them?

Was it Homo naledi?

We don't know.

And this creates a problem for us.

How do we tell when there are possibly two cultural hominins

in the same continent, who made what?

We don't know.

These pigment blocks from Olorgesailie,

again, Alison's work, are among the earliest uses

of pigment anywhere in the continent.

And what Olorgesailie is also known for

is a much earlier deposit, more than 800,000 years old,

including lots and lots of hand-axes,

including this extraordinary pavement of hand-axes

that the walkway is built around there.

Those hand-axes are coeval

with a hominin specimen from Olorgesailie

that when Rick Potts described it, he said,

"Well, this looks like a frontal bone that might be

a very small Homo erectus."

In today's context, this looks like a ringer for a later,

250,000 year old Homo naledi.

When we look at small-brained hominins in Africa,

they're associated with, in temporal terms,

lots of different technical abilities.

The question is, how can we pin down who made these things

and who's responsible for them

and whether they interacted with each other?

This is a serious question.

How did Homo naledi managed to coexist With other

much larger-brained hominins, for as long as it did?

We don't know.

When we established the earlier part of the

Homo naledi ancestry, like, "Where did it come from?",

the tool that we have to do that

is with phylogenetic analysis.

I'm showing you here a phylogenetic analysis

from Mana Dembo and colleagues, including Mark Collard,

who's introducing us all in the room,

that shows their favorite result was that Homo naledi

was connected to Neanderthals, modern humans

and other larger-brained species of Homo,

including Homo antecessor.

If that's true, that would put the origin

of the naledi lineage earlier than the date

of the antecessor fossils,

which is around 800,000 years ago.

So, it makes the naledi lineage something like

900,000 to 1,000,000 years old.

However, the mixture of anatomy of Homo naledi

makes it very difficult to be confident about

how it's related to us.

Another analysis by Debbie Argue and colleagues;

they were looking at the relationships

of Homo floresiensis in Flores, but they did so

by looking across the whole skeleton and traits,

and naledi is a really great sample for that.

In their favorite analysis, naledi was connected

to the fossils from Dmanisi, Georgia,

which are very early examples of Homo erectus,

or in this analysis called Homo georgicus.

If naledi is connected to those fossils,

then its lineage might be more than 1.8 million years old.

We don't know how long this branch

of our phylogeny was hanging out in Africa,

in coexistence with other species.

And it raises the question of how did

all this coexisting happen.

We've heard already, today, from a couple of people

about the need to explain isolation in an African continent

where it's clear that anatomical diversity

among large-brained hominins is very great.

We have a small-brained hominin

that existed throughout this entire time period.

Here's a modern human.

And you guys have heard a couple of times already today

and I'll briefly review.

We sort of think we know what the ancestry

of modern humans looks like.

You have these early anatomically modern forms

that existed within the last 200,000 years.

Before that, in Africa, you had fossils that many people

have described as early Homo sapiens, but not modern,

that existed before 250, back to maybe 400,000 years ago.

And across that time, and earlier, back to 600,000,

you have some very archaic looking hominins,

that any people have called Homo heidelbergensis,

for some Homo rhodesiensis.

The Bodo fossil, there at the bottom, is an example of that.

And that looks like a gradual pattern.

It's become apparent that this is a very diverse group.

And in the middle of that diversity is a species

that nobody expected to find.

How was this coexistence possible in an African ecology,

that as large as Africa is,

we think of ourselves as the ultimate competitors.

We're supposed to be driving all these things to extinction.

And they're doing fine.

That raises the question of whether naledi is part

of this network of mixture that existed across Africa.

And I'll give my best attempt at this mixture.

And you're gonna see some genetics later today.

This is drawn from genetics and so I just want to illustrate

that we've got a complicated tree of humans.

And at the bottom of this tree,

I've illustrated here, Neandertals and Denisovans,

you're gonna hear a lot about them later.

In a paper that just came out yesterday,

Alan Rogers at the University of Utah, and colleagues,

have pointed out the possible existence

of a super-archaic mixture into the ancestors

of Neanderthals and Denisovans.

So, there's complexity in their origins.

If we look at Africa, we see equivalent complexity.

We see the diversification of today's African groups,

starting before 300,000 years ago.

And archaic African groups as different from today's people

as Neanderthals and Denisovans that existed and contributed

into recent African populations.

Who were these people?

A lot of times, people look at the stem of this,

who's the common ancestor of us

and Neanderthals, for instance?

And say, "Well, there's something like Bodo,

"something Homo heidelbergensis."

But of course, that particular fossil or others like it

might be off to the side somewhere,

one of these archaic groups.

We look at the earliest members of our own species,

things like the Jebel Irhoud specimen and say,

"Well, maybe that's sort of rooting Homo sapiens in some way

"but we don't have any genetics.

"Maybe it's also off to the side in some way."

When we talk about Homo naledi,

I'm not going to put it at the root of Homo sapiens.

But is it one of these archaic branches that existed,

that maybe contributed to humans?

Does the mixture between these possible populations

explain something about the anatomy of naledi

and its unique mixture?

Or is naledi off to the side, totally separate?

Or is it deeper rooted; one of these super archaic branches?

We don't know.

It's a fascinating question, it's one that drives us.

Finally, how complex was this behavior that led naledi

into these cave chambers?

A lot of people have looked at this

as maybe an early example of burial.

And when we look at these sites and say,

"Why is it that this hominin is there

"in isolation, in abundance?"

There is something very interesting about it.

We're studying the bones to try to determine this

and we're back in the cave trying to find answers.

This is (murmurs) excavating the base

of the shoot, in 2018.

You see here, Becca Pichardo, suspended over a ladder

excavating what became very clearly another feature,

which is the articulated hominin's specimen

that we've brought out of the cave

in a plaster jacket, we're now studying.

Our further explorations in the cave system

have found additional instances of naledi material,

including additional find-spots deep into very narrow cracks

off of the main Dinaledi chamber, in places that our team

has to wedge themselves sideways and reach down

toward the floor, suspended off of the floor to reach.

It's clear that this hominin was spending a lot of time

in this cave, that it was very familiar

with the deep parts of it, and that the cave

was something interesting and special in its behavior.

And that says something about complexity,

understanding that, how it's connected to us?

What it might mean, whether it's connected to ritual

or other things that we've considered to be uniquely human,

is something that we're going to take a long time

to try to understand.

And so, it's an exciting moment because we're finding

these unexpected things, and that's always exciting.

But it also means that we have so much left to do.

I hope that all of you will follow us

as we continue this research.

And as we continue to make more discoveries

in the Rising Star Cave system.

Also, I hope that all of you who are out there digging,

keep your eyes open.

(laughter)

Because there's more of them out there.

And I think that we're going to see

many more of them very soon.

All right, thank you, everyone, I appreciate it.

(crowd applauds)

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The Description of CARTA Presents The Origins of Today's Humans - John Hawks, How Homo Naledi Matters to Our Origins