National Geographic: Mysteries of Mankind

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The earth does not easily yield

its secrets.

Yet around the world scientists

are unraveling

the compelling story

of human evolution.

It is a saga that blends the rigors

of science

with the romance of a detective story.

We have only traces that hint

at who our ancestors were

and how they may have lived.

It is like a gigantic puzzle with

most of the pieces forever missing.

Today, biological scientists may

quibble over the details of evolution,

but they all agree that evolution

is a fact.

Animal studies now shed light

on why some distant ape like creature

became an upright walker

and how it may have confronted

the perils of life on open ground.

Once barely noticeable

on the landscape,

humans would come to

dominate the earth.

The tool, mother of all inventions,

was a key to our success.

Tools chipped from stone helped

bring us to where we are today.

Now new tools help us

better understand what paths

we may have traveled along the way.

Much of our current knowledge

our understanding of who we are

and where we came from

has come about only

in the last 30 years.

Can we reconstruct the past?

Can long silent voices be summoned

across the vast reaches of time?

Join us as we probe

the MYSTERIES OF MANKIND.

By nature mammals are

intensely curious.

We humans are the most curious of all.

And perhaps nothing arouses

our curiosity

more than the intriguing question

of our origins.

What about the cavemans?

Caveman?

Well, what do you think he is?

A caveman.

At the close of the 16th century

when William Shakespeare wrote:

All the world's a stage, and

all the men and women merely players,

no one had any concept of the

vast array of players who preceded us.

Today we yearn to know iust

who the actors were

in this greatest of dramas.

When did they appear on the stage

and when did they finally depart?

The story is elusive at best,

like peering into mists that float

above an unfamiliar land.

Here and there through a dusky veil

we think we catch a fleeting echo

of some distant call

feel primordial eyes watching us

across the ancestral dark.

A thread of kinship surges within us.

Then, iust as we grasp at a clue,

the phantom voices melt away.

In the early 1900s the scientific

world believed that the cradle

of mankind was in Asia.

Then, in 1924,

South African anatomist Raymond Dart

was brought a skull workmen had found

in a limestone quarry.

Dart outraged the scientific community

by announcing that this primitive,

apelike child

was a hominid a member

of the family of man.

And, he said,

it had walked upright iust as we do.

Dart named the species

Australopithecus africanus

southern ape of Africa.

For more than a decade

Dart's only vocal supporter

was paleontologist Robert Broom.

Dart was finally vindicated

when Broom, in the 1930s and 40s,

discovered an assortment of

adult australopithecine fossils.

Africa's Great Rift Valley has been

geologically active

for millions of years

an ideal setting for the burial

of fossils and their later re-exposure

here, Olduvai Gorge would become known

as the '"Grand Canyon of Evolution'"

because of two maverick scientists.

Coming here in the 1930s,

Louis Leakey and his wife, Mary,

undertook one of

the most persistent efforts

in the history of anthropology.

What particularly excited the Leakeys

about Olduvai

was the presence

of primitive stone tools

scattered across the eroded landscape

Their passionate dream:

To find the remains of the creatures

who fashioned these tools to find

the earliest known human.

It would be nearly a quarter

of a century

before their single-minded

perseverance finally paid off.

The year was 1959.

We appeared to have got

what we were looking for.

Here at last was a man or

a man-like creature,

apparently the earliest known man

in the world.

It would turn out to be a

teen-aged male,

and not a true human,

but a more primitive hominid

an australopithecine.

And yet surely, like us,

he had cried when hungry as a baby,

wobbled his way onto two upright legs,

knew pain, love, and ioy.

Then in the way of all flesh, he died.

The boy died near the edge

of what was then a lake.

The skeleton is missing,

perhaps washed away or destroyed

by scavengers.

Fortunately,

the skull was buried by sediments.

Over the centuries water

soluble minerals turned bone to stone

as layer upon layer of deposits buried

the skull ever deeper into the earth.

Some layers were volcanic ash laid down

when a nearby volcano erupted.

Gradual geological uplift typical

of the Rift Valley

and subsequent erosion brought

the fossil once again to the surface.

The odds of finding a hominid fossil

are said to be one in ten million.

Because the Leakey's fossil was found

in a deposit with volcanic ash,

it could be accurately dated.

Volcanic ash contains radioactive

potassium that decays

into argon gas

at a known rate over time.

Human evolution was then believed

to begin no more

than one million years ago.

Yet here was

a fossil nearly double that age.

The scientific world was stunned.

Today, the addition of lasers

to the dating technique

enables scientists to date minuscule

samples even more accurately.

A single grain of ash,

seen magnified here many thousands

of times,

can produce a date much more

reliable than ever before possible.

The name and age of

a fossil tell little

about how the creature actually lived.

But perhaps the behavior

of living primates can.

Charles Darwin wrote that we are most

closely related to the African apes.

But at that time no one knew how

closely or to which species.

The answer would come from

a most unlikely source

the test tubes of molecular biologists.

Twenty years ago Dr. Vincent Sarich

and his colleagues at the University

of California

were among a small group of scientists

dating evolution with molecules

and test tubes instead of fossils.

Sarich's group compared a blood

protein in 13 species of primates,

including humans,

and charted when each had diverged

from a common ancestor.

The dates differed radically

from those obtained from fossils.

Among the great apes,

beginning millions of years ago,

the line that led to orangutans

was the first to split off

from a common ancestor.

The evidence suggests gorillas

were next.

According to Sarich,

chimpanzees and man

may have diverged as recently as four

to five million years ago.

Such a recent divergence

was almost impossible

for many scientists to accept.

Laymen were equally reluctant

to listen.

There is still a very strong

resistance to looking

at human beings in an evolutionary

context, especially behavioral.

Because we want to

retain a separateness.

We don't want to see ourselves

as having any non-human

in our ancestry.

There are significant differences

between us.

We are essentially hairless

Oh, he likes the beard.

We are habitually upright walkers,

we have a much larger brain,

and we have the gift

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