Out of the Cradle

The earliest known hominids

were born in Africa,

and we homo sapiens were also born here.

But the evolutionary path to our species

was neither flat nor straight.

Through the evolutionary process,

the relatives of humanity split

into roughly 20 species.

Some of them coexisted and were fierce rivals

in the struggle for survival.

The species we descended from

were not the physically strongest.

In fact, they were among the weaker.

They survived periods of intense difficulty,

staging a series of amazing comebacks.

Today, there are 7.6 billion homo sapiens on earth.

We are the planet's dominant species.

How have we achieved this success?

We look for answers at the dawn of humanity.

Africa, the cradle of the human race.

The first hominids took their first steps

on this terrain.

Deep in the jungles lies an animal

that can help us imagine the origins of humanity.

These are chimpanzees.

Humanity's family tree diverged from chimpanzees

about seven million years ago.

Chimps are our oldest surviving relatives,

so human evolution is often illustrated

with a stereotyped expression

of one single path,

from bent over chimps to upright modern humans.

But the story was not so simple.

There used to be many other hominids

besides we homo sapiens,

and we continue to discover more.

We currently know of roughly 20 different species.

At times, multiple species are though to have coexisted.

The path leading to homo sapiens looks like this.

The other lineages became extinct

without leaving evolutionary descendants.

An important hominid that paved the way to our existence

was ardipithecus ramidus.

A. ramidus is the oldest hominid species

confirmed to be bipedal.

It lived in forests

but started walking on two legs.

This was rare in the forest

and seemingly a disadvantage,

but A. ramidus won out against the quadrupeds.

What was the secret to its success?

A clue to answering this question

was discovered in Ethiopia.

This is an archeological site called Middle Awash.

You finished up here?

For many years, Tim White

has been leading an international team

in excavating this site.

Then we reach the fault.

Nice, baby monkey.

This is a Columbus monkey, leaf-eating monkey.

Died 4.4 million years ago.

Finds made here by White and his team

have revealed that this landscape was once a vast forest

and that it was home to an ancestral hominid species

with some surprising features.

Yes!

Proximal hand phalanx, ardipithecus ramidus!

Over a decade,

they restored hundreds of hand collected bones

and revealed the bodily features of an early hominid

that lived 4.4 million years ago.

Ramidus was approximately 120 centimeters tall.

It had an unusual body,

with a small head and long arms and legs.

Its feet were shaped like a monkey's

and were capable of grabbing things.

This indicates that ramidus lived in trees.

Its pelvis, however, is different from an ape's.

Let's compare with a chimpanzee.

A chimpanzee has a long and narrow pelvis.

How about ours?

The human pelvis is broader.

It supports the organs that move down when we stand up.

Ramidus has a rather wide pelvis

that more closely resembles a modern human's

more than a chimpanzee's.

In short, ramidus was probably bipedal.

It started walking on two legs

while still living in the trees.

This overturned the common theory

that bipedalism started in the grasslands

after hominids left the trees.

And the evidence of ardipithecus

has revolutionized the way people think

about human evolution,

because you can no longer think of something

halfway between a chimp and a human.

You have to think outside that box.

You have to think something unique.

And there are hundreds of individuals,

of monkeys and birds,

all of the mammals that lived here

as well as fossilized vegetation.

We have wood, we have seeds.

We have an environment today that you need a hat in.

In the days of Ardi, you wouldn't need the hat so much

because it was not a desert.

It was a woodland here

with ardipithecus both able to move in the trees

and to walk on the ground.

Based on the latest evidence,

this is what the surrounding environment

probably looked like to ramidus.

When down on the ground,

ramidus is vulnerable to predators.

Ramidus wasn't as good at climbing trees as a monkey

and it couldn't run very fast.

So how did it win out in the race for survival?

That is today's first comeback story.

The key to ramidus's success

laid in the environment they lived in.

The era ramidus walked the forest,

there was a cataclysm in Africa.

It turned out to be a lucky break for bipeds.

The earth's mantle shot up and formed mountain ranges

that tore Africa apart.

These mountains blocked clouds.

The eastern part of the continent

became increasingly arid

and the forest dwindled.

A lush forest, a paradise for animals,

became something else.

Now, trees were sparse

and fruit and other food was hard to come by.

The bipedal ramidus suddenly had a great advantage

because it was good at carrying food long distances.

A geological cataclysm proved to be

a huge break for a humble forest walker.

In the competition for survival,

ramidus won and unexpected victory

over other species better suited to the trees.

Research has also uncovered a major development

in ramidus's behavior that is still with us today.

Four million years ago,

ramidus seems to have had a family

much the same way as we do.

Scientists are finding the proof to back this up.

Owen Lovejoy is an expert in the analysis

of A. ramidus fossils.

One of the striking things that we find

associated with Ardi

and the appearance of upright walking

is the fact that there was another, simultaneous,

major change occurring,

and that was in the dentition.

In other words, in the teeth.

In ramidus, the upper canine

and the size of the crown is vastly reduced.

These are the canines of a male ramidus.

Compared to a chimpanzee,

ramidus has very small canines.

The canines of male chimpanzees are thought

to have developed as weapons to fight over females.

The relatively small canines of ramidus

could be evidence that males did not fight over females.

Dr. Lovejoy theorizes this would imply

that ramidus practiced monogamy.

In other words, it had only one mate at a time.

This lifestyle would have been beneficial

for successfully producing offspring

in a dwindling forest.

What you're doing is instead of wasting the male's energy

in simply competing with other males

for access to a female,

you're instead using his energy

to the reproductive vantage of the pair.

So there's really a fundamental advantage of pair bonding

in terms of the rate of reproduction,

so we think that that would have increased

the level of cooperation amongst the females and the males,

and that would have been one of the reasons why

early hominids were so demographically successful.

A natural event proved to be

a happy accident for an early hominid

that walked on two legs.

And this new natural environment encouraged monogamy.

Hominids became creatures with families.

Ramidus shifted into family life

and eventually gave rise to a few different species,

but only one offspring lineage survived,

from which australopithecus afarensis evolved.

This hominid is the star of our next comeback story.

Ramidus was about 120 centimeters tall.

The male afarensis stood about 150 centimeters tall,

a difference of 30 centimeters in height.

Ramidus had feet like hands,

adapted to grab tree branches.

The feet of afarensis were probably not as dextrous.

They were almost perfectly adapted for life on the ground.