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[Music]
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[Music]
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humans without a doubt the smartest
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animal on
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earth yet we're unmistakably tied to our
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ape
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Origins millions of years ago we were
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Apes living ape lives in
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Africa so how did we get from
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that to
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this what happened what set us on the
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path to
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humanity the questions are huge but at
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last there are answers more than 6
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million years ago we took that first
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step to separate from the Apes we see
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the launching of the career that
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ultimately led to Homo sapiens and 3
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million years ago we see the root of our
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big brain begin to take hold in a tiny
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creature more like a chimp than a human
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the frontier of human evolution is
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really being brought to this razor sharp
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edge and we now know that for millions
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of years many different humanlike
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species live together on the planet
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until one day there was only
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us Homo sapiens the most complex
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adaptable animal on Earth so how did we
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get this way and why a radical new
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Theory reveals how episodes of
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cataclysmic change forced our ancestors
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to adapt or die I think we should
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actually look to our proud ancestry and
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how we evolved in East Africa and say
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that's how we survive that we can
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survive the future so get ready for a
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ride through millions of years of our
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history it's the story of becoming human
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our story
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right now on Nova
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[Music]
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millions of years ago on the plains of
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Africa a momentous event took
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place Apes that had walked on four legs
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stood up and walked on
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[Music]
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two eventually this change in posture
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would be followed by a change in their
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brains
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somehow over time they would become
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us we know it happened but we've never
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known when or
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why until
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now in the Sahara Desert a 6 milliony
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old fossil called tumai May hold the
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secret of how we first walked upright
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we are writing the first chapter of
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human
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evolution we are very close to the
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beginning very
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close and the fossilized bones of a
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child from 3 and2 million years ago hint
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to us about the beginnings of human
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thought we're discovering how many
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different human species lived on Earth
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at the same time and why all but one
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died out
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we Homo sapiens are the first ever to be
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alone so what powered our Evolution why
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did we become
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human scientists are scouring the most
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remote parts of Africa for
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Clues the search for answers begins here
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in the afar Northeastern Ethiopia
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it's part of the Great Rift Valley a
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deep cut in the Earth where geologic
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forces are ripping Africa
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apart millions of years of History are
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brought to the surface in layers of
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exposed
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[Music]
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rock it's hot and
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desolate dangerous
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too ancient rivalries and modern weapons
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have turned the afar into a No Man's
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Land of simmering
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conflict but zarai aliman has made this
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forbidding place his life's
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work he's searching for the fossilized
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traces of our earliest human
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ancestors the fossil bones of animals
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like antelopes elephants and pigs are
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abundant but the fossils of our
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ancestors are extremely
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rare then in a stroke of luck zarai
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makes the find of a
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lifetime a find that illuminates our
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origins in a unique
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way on that afternoon we decided to
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survey this
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Hillside and the first thing that was
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spotted was a cheekbone of the face
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it was a face so tiny it had to be a
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baby but not a baby chimp he could tell
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that from its
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shape the skull was embedded in
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Sandstone but as aai turned it over he
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could see more bones
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inside everything was squashed against
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uh the base of the skull and completely
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covered by Sandstone block
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Clues to the age of the fossil came from
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a distinctive feature in the
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landscape white bands of volcanic ash
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and that is a volcanic ash dated to 3.4
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million years
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ago if the volcanic ash is 3.4 million
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years old zarai fossil which was lying
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just above it must be younger
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it was a child from the dawn of human
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evolution about 3.3 million years
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ago zarai called the baby
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Salam the Ethiopian word for
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[Music]
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peace then he set off on a quest to
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unravel her many
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Mysteries her journey began a very very
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long time
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ago imagine the entire span of recorded
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human history taking us back to the
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Egyptian pyramids about 5,000 years
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double it 10,000 years ago when plants
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were domesticated and agriculture
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begins double it again to the time when
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Ice Age Hunters paint stunning images on
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Cave walls
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and keep doubling six more
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times taking us back 1.3 million
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years when the first creature who really
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looked like us hunted on the plains of
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Africa and then keep traveling back
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another 2 million years and only then do
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we arrive in the time when Salam lived
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in Ethiopia nearly 3 and 1/2 million
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years ago
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what were Salam and her family
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like what kind of world did they live
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in the answers are hidden in their
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fossil
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bones Adis Ababa
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Ethiopia zari's
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home he's one of a whole new generation
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of African scientists trying to unravel
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the mysteries of human
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Origins zarai has brought his precious
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fossil here to the National
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Museum his challenge is to release her
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from the tomb of sandstone in which her
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bones are
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[Music]
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encased he quickly identifies her she's
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from a species considered by most
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scientists to be an ancient
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ancestor ostr opacus afarensis a small
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chimp-like creature who walked on two
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legs this is the same species as the
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famous Lucy discovered in the 1970s by
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Don
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Johansson Lucy was terribly important
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because she was really an amalgam and
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she of of different characteristics of
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ape and
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human I think specimens like Salam and
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Lucy are extraordinary simply because
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you can look at them and see evolution
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in the making
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[Music]
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but seeing evolution in the making will
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take some work salam's fossilized bones
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are solid
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rock held together by a mesh of soft
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Sandstone it has to be painstakingly
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removed you spend hours hours and hours
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and days and years and years and then
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removes the sand grains grain byrain
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working every
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day he's been at it for eight long years
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but the payoff has been
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[Music]
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amazing as the work progressed zarai
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revealed an almost complete
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[Music]
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skull and tucked beneath it was nearly
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her entire spine along with both
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shoulder
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blades other bones were found nearby
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an almost complete
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foot this is the
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kneecap the TV
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here never before had a child skeleton
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been found so ancient and so complete
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her bones would fit in a shoe box but
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they speak volumes about her
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life for example to find out how old she
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was when she died
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zarai looked at her teeth but not the
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baby teeth visible in her
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jaw the adult teeth growing inside the
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bone as seen in a CT
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scan from that we know Salam died at age
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three like Lucy she testifies to a
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crucial step in our
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Evolution unlike like apes these
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creatures walked upright as the first
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fossil Don Johansson found clearly
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revealed it was scking out of the ground
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like that and I gently tapped it with my
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uh sneaker and this is what fell out of
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the ground and it is the this is your
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the top end of your shin bone so the
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kneecap would sit right in here and very
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close by in two pieces I found this bone
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and when you put them together and you
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see how they move and
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articulate that it has all the Hallmarks
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of uh of an upright
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person other bones confirm that Lucy
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walked on two legs like us this is
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Lucy's pelvis and uh in a and you can
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see how different a chimpanzee is and
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the reorientation of these these hip
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bones in a in a chimp they're facing
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straight forward so here's this is this
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is what every body is sitting on in
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their living room right now so they're
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not
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identical but clearly these two resemble
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each other much more closely right then
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either one of these uh resembles the
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pelvis of of an
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ape from the waist down Lucy was like
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us from the waist up she and her kind
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were all
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eight Salam skeleton is the the same
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with chimp-like shoulder blades giving
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her the range of motion needed for
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climbing and
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Swinging these ancient creatures Must
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Have Spent time in the
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trees possibly sleeping there at night
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to keep away from
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predators but walking upright on the
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ground during the
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day they were at home in Two
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Worlds what was their environment
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like it must have been very different
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from the Great Rift Valley of
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today across the border in Kenya is one
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of the hottest and most Barren places on
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Earth a vast expanse of volcanic rock
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and burning
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desert that's how it is now
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but there's good evidence that for most
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of its history it was very
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different researchers braving
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temperatures over 100° are seeing signs
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of a dramatic transformation here in the
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seuda
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valley the seuda valley was entirely
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covered in water up to an elevation of
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about 580 M so you can imagine that
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that's all this Valley were filled by a
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huge Lake a huge Lake that's deeper than
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any of the Great Lakes in fact the
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entire African continent used to be a
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lot wetter than it is
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today many millions of years ago long
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before Salam and Lucy Africa was a wet
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tropical environment covered with
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rainforest this is where the ancestors
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of Salam and Lucy
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lived they probably looked a lot like
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chimps but then Africa started to
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gradually dry
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out the rainforest began to
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shrink by salam's time 3 to 4 million
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years ago the Great Rift Valley was a
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mosaic of different
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environments we know that from the
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fossils of the animals that lived
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here their bones litter the
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ground this is a canine of a
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hippopotamus so this is probably a
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skeleton of a
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hippopotamus how can one find hio in
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this type of
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environment being nice anti the fossils
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tell tell the story of a vanished
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landscape this is a Laro of an
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antelope 3 million years ago the rift
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valley was a patchwork of grassy
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Plains scattered
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Woodlands lakes and rivers definitely
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very different from what we see here
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today wow a nice big here as their
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environment changed scientists believe
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our ancestors changed too
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[Music]
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they had been creatures who spent most
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of their time in trees like chimps and
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orangutangs
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today but as their forests shrank some
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of them develop the trait that we take
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for
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granted
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bipedalism walking on two
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legs this is one of the defining
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characteristics of humans
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but how did bipedalism develop and
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why bipedalism is such an unusual trait
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there's no other mammal that habitually
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walks on two legs like we
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do because it's Unique it's hard to
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figure out why it
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happened there are a lot of
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[Music]
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theories one of them is that they stood
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up to be able to see over Tall Grass
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another theory they stood up up to be
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able to pick fruits off of the low
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branches of trees the way chimpanzees do
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today another theory states that they
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stood up to cool more efficiently so
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that we don't have as much sun beating
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on so much of our
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body and I think the most compelling
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idea the most compelling hypothesis is
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that it saved us energy and energy is
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crucial to survival
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[Music]
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let's go back to the dense forest home
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to our ancient ape ancestors 10 million
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years
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ago like many Apes today they were
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perfectly suited to a life in the
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trees they're very good at climbing in
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trees they're phenomenal at climbing in
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trees on the ground these ancestral Apes
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could probably walk on two legs for
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short distances if they had to carry
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something
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fantastic climbers but also able to walk
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and run rapidly and effectively but not
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economically walking was tiring but they
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didn't have to walk
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far but if you're chip and you only walk
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2 to 3 km a day doesn't really mean much
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right it's not it's not going to have
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that much of effect on your energy
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budget but energy demands would change
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as the force started to
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disappear our ape ancestors had to walk
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walk more they have to go farther to get
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from one fruit patch to another fruit
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patch for
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example Dan Lieberman is an expert on
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bipedalism in Apes for example he
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believes that walking on two legs
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evolved because it saved
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energy when you compare the energy
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consumption of humans to chimps there's
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no
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contest a chimp is an energy glutton
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it spends enormous amount of energy
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about four times as much energy as a
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human
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walking whether it walks on four legs or
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two a chimp can't compete with a human
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gate it's poorly designed to withstand
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the forces of gravity it has to spend a
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lot of muscular effort to keep itself
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from collapsing into a little pile of
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chimpus or whatever with each step
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according to libran small anatomical
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differences created large Energy
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savings setting our ancestors on the
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path to
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bipedalism a path that would eventually
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lead to
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us but how long did it
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take when Lucy's kind were first
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discovered many people thought they were
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the so-called missing link between apes
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and humans
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but the science of genetics has
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transformed our understanding with the
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technique called the molecular
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clock today scientists can compare DNA
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from closely related species to find out
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how long ago they split from a common
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ancestor it's just a very simple idea
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that the rate of change in DNA sequences
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is more or less constant over time and
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that's an extraordinarily powerful
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concept because it means that you have a
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way of determining when two species last
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Shar to common
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ancestor living forms evolve because DNA
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sometimes spontaneously changes as it
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copies
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itself these changes happen at a
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surprisingly regular
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rate by counting the differences between
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the genetic code of chimps and humans we
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can calculate how long they've been
00:22:01
evolving away from each other the dates
00:22:05
that one almost always gets are around 5
00:22:08
to 7 million years ago for when humans
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and chimpanzees last shared a common
00:22:13
ancestor here was proof that humans
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diverged from the Apes much earlier than
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we thought about 6 million years
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ago it shows Lucy and Salam weren't one
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step removed from chimps but
00:22:30
many they may even be closer to us than
00:22:33
to the first human
00:22:36
ancestor so what came before Luci and
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Salon who was our earliest
00:22:49
ancestor until the 1990s the fossil
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record was
00:22:54
[Music]
00:22:56
blank fossil Hunters combed East
00:22:59
Africa's Great Rift Valley but could
00:23:01
only find small fragments older than 4
00:23:04
million
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years then in 1997 a French
00:23:11
Anthropologist called Michel brune
00:23:14
decided to look somewhere
00:23:16
[Music]
00:23:20
else we decided to go to
00:23:23
Africa but to the
00:23:26
west to the west of the Great
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drift 1,600 mil to the West at the edge
00:23:34
of the Sahara desert in Northern
00:23:38
Chad obviously if you only go to the
00:23:41
field in East
00:23:42
Africa then you are going to find
00:23:44
fossils only in East
00:23:48
Africa this was the
00:23:53
situation Michelle was looking in a
00:23:55
place where the few animal fossils he
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turned up were all around 6 million
00:24:00
years
00:24:05
old no one expected any humanlike
00:24:08
fossils to be found in a layer that
00:24:12
ancient no and everyone said no there
00:24:15
just aren't any fossils
00:24:18
there Michelle was not to be deterred he
00:24:21
was stubborn many thought to the point
00:24:23
of
00:24:25
madness he and his team spent years
00:24:28
searching the desert for signs of our
00:24:30
ancestors and year after year they came
00:24:34
up
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empty then on their 26th expedition in
00:24:39
2001 they found a smashed misshapen
00:24:45
skull around 6 million years
00:24:50
old they called it sahelanthropus
00:24:54
jadensis there were no bones apart from
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the skull
00:25:00
could it be a human ancestor or just
00:25:03
another ape the skull was so deformed it
00:25:06
was difficult to
00:25:09
tell Michelle would have to reconstruct
00:25:16
it his first step was to take the skull
00:25:19
now nicknamed tumai to a particle
00:25:22
accelerator in grobla
00:25:24
France to use its powerful X-Ray Scanner
00:25:31
over a thousand pictures of the fossil
00:25:33
were taken to build a 3D image of the
00:25:36
crushed
00:25:38
skull using the virtual image the skull
00:25:42
could be restored to its original
00:25:45
shape it was then reproduced by a type
00:25:48
of 3D printer equipped with lasers which
00:25:51
hardened
00:25:53
plastic when it finally Rose from its
00:25:56
bath the cast of two m skull was ready
00:25:59
for detailed
00:26:05
study the cast allows Michelle to answer
00:26:08
an important
00:26:10
question did this ancient creature walk
00:26:13
on two legs millions of years before
00:26:16
Luci or
00:26:19
Salon it's how the skull connects to the
00:26:22
spine that provides the vital
00:26:26
clue and Michelle could defer that from
00:26:29
the shape of tumi's
00:26:31
skull if tumi's skull is set on the neck
00:26:34
of an ape that walks on all fours his
00:26:37
eyes Point downward that can't be right
00:26:41
set on the upright spine of a bipad his
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eyes Point straight ahead for Michelle
00:26:47
this proved tumai walked
00:26:54
upright anatomically speaking he had a
00:26:57
receding back skull of a biped the back
00:27:00
of his skull is not that of a gorilla
00:27:04
like some people are trying to say no no
00:27:07
no not at all all you have to do is
00:27:12
look some scientists still question
00:27:14
whether tumai was really a
00:27:17
biped but if Michelle is right his 6
00:27:20
milliony old fossil is a good candidate
00:27:23
for the first human ancestor
00:27:28
discoveries like this are changing the
00:27:31
way we see human
00:27:35
evolution scientists used to have a
00:27:38
simple idea the growth of open
00:27:41
grasslands forced our ancestors out of
00:27:43
the
00:27:44
trees they became bipeds and in short
00:27:48
order brain size
00:27:51
increased human evolution took off we
00:27:54
were on our way to becoming human
00:27:59
that simple idea prevailed for more than
00:28:02
a century Darwin thought that we left
00:28:05
the trees uh walked on the ground
00:28:07
upright freed our hands made tools got
00:28:10
big brains reduced our canines and so on
00:28:12
all at the same time but walking upright
00:28:16
may not have automatically led to big
00:28:18
brains at all from tumai to Salam both
00:28:22
bads brains stayed
00:28:26
small and they weren't the the only
00:28:29
ones over millions of years there was a
00:28:32
profusion of upright Walkers with
00:28:35
complicated names and chimp sized
00:28:39
brains like auroran Tanis what we're
00:28:42
seeing is a fluoresence of species
00:28:44
multiple species they're probably subtly
00:28:46
different from each other arpus raminus
00:28:49
but it's important to recognize that
00:28:51
they're not major differences among
00:28:53
these species ostr Opus
00:28:56
Africanus they were bipeds big snouts
00:29:00
more or less chimp sized
00:29:02
brains kenyanthropus plat
00:29:05
UPS this way of life this Suite of
00:29:09
adaptations lasted for millions of
00:29:12
years small brained bipedal Apes were
00:29:15
extremely successful debates rage among
00:29:19
scientists about which one eventually
00:29:22
led to
00:29:24
us but as a group they flourished for
00:29:27
about 25 times longer than we've been
00:29:33
around they survived and thrived as
00:29:36
brain size flatlined for almost 4
00:29:39
million
00:29:44
[Music]
00:29:47
years but that doesn't mean nothing
00:29:53
changed there's evidence that the seeds
00:29:55
of our Humanity were growing in these
00:29:58
aplike
00:29:59
[Music]
00:30:00
creatures one key difference between
00:30:02
humans and apes is the length of
00:30:08
childhood but what do we know about the
00:30:10
childhood of our early
00:30:13
ancestors we knew all about the adult
00:30:15
individuals but we didn't know much
00:30:17
about the
00:30:20
children the brains of baby chimps have
00:30:23
an early growth spurt they're almost
00:30:25
fully formed by age three
00:30:29
in humans that growth spurt is slower
00:30:32
and it takes nearly two decades for our
00:30:34
brains to fully
00:30:37
[Music]
00:30:38
mature but what about salam's brain 3.3
00:30:42
million years ago but of course most
00:30:45
exit her skull tells us all we need to
00:30:47
know
00:30:50
this we have her milk
00:30:52
teeth you and her adult teeth which give
00:30:56
us her age
00:30:58
3 years
00:30:59
old and we have a cast of the inside of
00:31:02
her skull which tells us about her brain
00:31:06
uh when you have
00:31:08
this you can directly measure how much
00:31:12
of the brain was formed at age
00:31:17
three from other fossils we know how
00:31:20
large salam's Brain would have been as
00:31:22
an
00:31:24
adult so zarai could calculate how much
00:31:28
of her brain was already formed by age
00:31:30
three when she
00:31:34
died he knows what the answer would be
00:31:36
for a
00:31:37
chimp by age three a chimpanzee would
00:31:40
have over 90% of the brain
00:31:43
formed but salam's brain was only around
00:31:47
75% of its adult size suggesting it was
00:31:51
growing up slower
00:31:54
[Music]
00:31:58
childhood would have been her time to
00:32:00
learn to learn the survival strategies
00:32:03
her family group needed to live in a
00:32:06
dangerous
00:32:10
World perhaps this set the stage for our
00:32:14
longer human childhood when culture is
00:32:17
handed
00:32:21
down but is there any other evidence
00:32:24
salam's brain was becoming more human
00:32:27
and less
00:32:30
eight to find out compare a human brain
00:32:34
to a
00:32:35
chips this is the brain of our closest
00:32:38
relative the chimpanzee brain slightly
00:32:40
larger than you would expect of a
00:32:42
typical primate for their body size not
00:32:46
greatly so there's a scientists look for
00:32:49
Clues to the evolution of the brain in
00:32:52
the folds and furrows on its
00:32:54
surface one important structure is
00:32:57
called the lunate sulcus when
00:33:00
chimpanzees as in many primates there's
00:33:02
this big deep sulcus here the the lunate
00:33:07
sulcus the lunate sulcus is a deep
00:33:10
Furrow in a primate's brain it divides
00:33:13
parts of the brain related to vision
00:33:15
from the rest of the
00:33:17
neocortex which is where more complex
00:33:20
thought
00:33:21
happens the human brain doesn't have
00:33:24
this deep Furrow and the neocortex is
00:33:27
bigger than the vision structures which
00:33:29
have moved far to the back typically
00:33:32
say so did Salam have the Deep Furrow
00:33:36
and small neocortex of a chimp or had
00:33:39
something
00:33:41
changed brains don't fossilize but her
00:33:44
remarkably complete skull provides a way
00:33:47
to see some of the different structures
00:33:49
of her
00:33:52
brain a cast of the brain case called an
00:33:56
endocast preserves the impression of the
00:33:58
brain
00:34:01
surface Ralph Holloway has a collection
00:34:04
of 300 brain endocasts from many of our
00:34:08
ancestors what a paleon neurologist like
00:34:11
myself will be looking for are those
00:34:14
indications on the endic casts that
00:34:16
might suggest reorganization taking
00:34:20
place and that's why things like the
00:34:23
so-called Infamous lunate sulcus becomes
00:34:26
important
00:34:28
Ralph claims that his chimp-like
00:34:30
ancestors evolved into creatures like
00:34:32
Salam and Lucy the lunate sulcus the
00:34:36
furrow marking the vision structures
00:34:38
moved back making room for a larger
00:34:43
neocortex the thinking part of the
00:34:47
brain if you look carefully what you've
00:34:49
got here is a depression that could very
00:34:54
likely be the lunate sulcus and so
00:34:57
that's suggest then by australopith
00:34:59
theine times that you you know you're
00:35:02
having a beast that is simply smarter
00:35:04
than present day
00:35:09
chimpanzees if that's the case although
00:35:12
still the size of a chimps salam's brain
00:35:15
had been
00:35:17
rewired but there was a long way to
00:35:25
go she and her kind were still very
00:35:28
apelike
00:35:29
[Music]
00:35:33
it would take another million years for
00:35:36
the seeds of humanity contained in
00:35:38
salam's tiny frame to bear
00:35:44
fruit it's a Time still shrouded in
00:35:48
mystery for almost half a million years
00:35:51
the fossil record is virtually
00:35:54
silent but in this blank period
00:35:57
something something is
00:36:00
happening in 2 and 1/2 milliony old
00:36:03
layers scientists begin to find
00:36:05
something
00:36:06
[Music]
00:36:08
new we might be tempted to call them
00:36:11
rocks but someone was shaping
00:36:14
them they are the first stone
00:36:18
tools the way we know this is a tool
00:36:20
instead of just a broken rock is that
00:36:23
it's broken in um a very particular way
00:36:26
breaking a flake off this way that way
00:36:29
this way back and forth so there is a
00:36:32
method behind how this rock was broken
00:36:36
in in order to make it into a tool and
00:36:38
it's not a random
00:36:40
method it's considered unlikely they
00:36:43
were made by ostr opacus Lucy's
00:36:47
kind ostros was around for a couple of
00:36:51
million years and did not make stone
00:36:53
tools but if not Lucy's kind then who
00:36:58
the Gap in the fossil record makes it
00:37:01
difficult to
00:37:03
say but that's not surprising tools
00:37:06
preserve easily bones much less
00:37:11
so finally the skulls of a new creature
00:37:15
begin to turn up is this the tool
00:37:18
maker the skulls are different from what
00:37:20
came before they represent the dawn of a
00:37:24
new era beginning around 2 million years
00:37:27
ago
00:37:30
this is our era the era of the genus
00:37:34
homo
00:37:36
humans the mysterious tool maker homo
00:37:40
Havis is the first of these new
00:37:43
creatures but we definitely have
00:37:45
evidence that the stone tools were being
00:37:48
used to to break the long bones in order
00:37:51
to get to the marrow inside the long
00:37:53
bonees there were clear cut marks on the
00:37:55
bones of turtles crocodiles
00:37:57
big antelopes little antelopes even
00:38:00
hippos really big animals like hippos so
00:38:03
we know that meat had become an a new
00:38:05
important part of the diet of
00:38:09
homohabilis the first fossil to be
00:38:11
called
00:38:12
homohabilis included 21 bones of the
00:38:15
hand and was nicknamed
00:38:18
handyman this little bone is the bone at
00:38:21
the end of the thumb and that little
00:38:23
bone in homo Havis like in humans is
00:38:26
very Broad and the broad bone reflects
00:38:30
having a broad pad on the thumb with a
00:38:32
lot of surface area for fine Precision
00:38:35
grip with newly dextrous hands this
00:38:38
creature could make better
00:38:42
tools but what was it
00:38:46
like the few skeletal bones that have
00:38:48
been found indicate a creature much
00:38:51
smaller than us about the same size as
00:38:53
Lucy and salam's kind ostr opius three 3
00:38:57
to 4 ft
00:39:00
tall Homo habilis was still aplike in
00:39:03
many ways but with a critical difference
00:39:07
what we've see in the evolution of homo
00:39:09
Havis is an expansion in the brain size
00:39:13
compared to ostop pyus so here is the
00:39:15
skull of ostras and it has no forehead
00:39:19
it just has a straight slope behind the
00:39:20
orbits whereas here in homo halis you
00:39:23
see um a sloping elevated forehead and
00:39:27
in epicus the area behind the orbits is
00:39:29
pinched in also reflecting a small
00:39:31
frontal region in contrast in homo habis
00:39:34
we see an expansion of that area behind
00:39:37
the orbits that points to an expansion
00:39:40
in the cognitive capabilities of higher
00:39:43
functions of higher reasoning functions
00:39:45
of the brain it was an expansion
00:39:48
equivalent to a doubling of brain
00:39:51
volume once you go from something like
00:39:54
400 CC's and australopithecines to say 7
00:39:57
00 800 cc's in homohabilis yes you're
00:40:01
getting getting a big increase in
00:40:03
cognitive
00:40:05
capacity and along with his bigger brain
00:40:08
Homo habilis was starting to look a lot
00:40:11
more
00:40:14
human The Contours of fossil skulls
00:40:17
allow Reconstructionist Victor deck to
00:40:20
reveal the faces of early human beings
00:40:26
[Music]
00:40:27
gone is the projecting snout of an ape
00:40:31
in Homo habilis the face of humanity is
00:40:42
emerging this poses a great
00:40:47
Enigma why after millions of years of
00:40:50
flatlining did brain size and mental
00:40:53
capacities suddenly take off
00:40:58
[Music]
00:41:02
2 million years ago what jump started
00:41:05
human
00:41:12
evolution scientists all over Africa
00:41:15
looked for
00:41:17
Clues here in Kenya they found
00:41:20
some at the southern end of the Great
00:41:23
Rift
00:41:24
Valley it's a hot bed of tectonic
00:41:27
activity where ancient layers are forced
00:41:30
to the
00:41:33
surface 10 million years ago Africa was
00:41:36
a much wetter
00:41:38
place a tropical Jungle which has been
00:41:41
slowly drying out ever
00:41:46
since but these rocks in Kenya show that
00:41:49
Africa's gradual drying Trend was
00:41:52
punctuated by bursts of wild climate
00:41:54
fluctuation
00:41:57
Rick pots is an expert in reading the
00:42:00
Rocks this layer right here represents
00:42:03
about a thousand years of environmental
00:42:05
stability but then we had an Abrupt
00:42:08
volcanic eruption and then the lake was
00:42:10
around for perhaps 500 years before a
00:42:13
drought and the lake came back so in
00:42:15
some cases we saw this through layer
00:42:18
after layer of environmental
00:42:21
[Music]
00:42:23
change with his trained eye Rick could
00:42:26
see some layers were once Lake beds
00:42:30
others Desert Sands still others came
00:42:33
from volcanic eruptions a snapshot of a
00:42:36
million years of climate
00:42:40
history this observation led him to an
00:42:43
amazing new
00:42:45
idea rapid change as a catalyst for our
00:42:50
Evolution and I began to think that well
00:42:53
maybe it's not the particular
00:42:55
environment of a savannah that was
00:42:57
important but the tendency of the
00:42:59
environment to
00:43:01
change could it be that the need to
00:43:03
Survive Violent swings of climate made
00:43:06
our ancestors more
00:43:12
adaptable a group of scientists has come
00:43:15
here from Germany to find out just how
00:43:17
radical these swings of climate really
00:43:23
were it's hard to believe but these huge
00:43:26
Rock formations are made of the shells
00:43:29
of tiny one- celled organisms called
00:43:36
datom there are many different kinds but
00:43:39
they all live in
00:43:43
water their shells collect in layers of
00:43:46
rock that pile up over millions of years
00:43:50
proving that this whole valley was once
00:43:52
a giant
00:43:55
Lake and yunginger analyzes these Rock
00:43:59
samples under the
00:44:03
[Music]
00:44:06
microscope what I've discovered was that
00:44:10
those white layers consist of a special
00:44:13
kind of diatoms which only live in deep
00:44:17
legs but between the white layers she
00:44:20
also finds other species of datom which
00:44:23
only live in shallow water
00:44:27
it means that in this spot a massive
00:44:30
Lake appeared and disappeared and
00:44:33
reappeared many
00:44:36
times these Lakes are are really
00:44:38
significant these are not small or pots
00:44:41
and what we've been able to document now
00:44:42
is is a series of lakes that's are
00:44:47
cycling when we're talking freshwater
00:44:49
lakes the size of Lake Victoria filling
00:44:52
the whole Rift Valley and then
00:44:54
disappearing enormous amount of water
00:44:56
rushing in through this area this
00:44:58
constant Flux Of turnover of change an
00:45:01
awful time to live here it's not just a
00:45:03
unidirectional change it's going back
00:45:05
and
00:45:07
forth against the backdrop of a slow
00:45:10
drying Trend Africa was periodically
00:45:13
pulsing with climate
00:45:14
change wet dry then wet again sometimes
00:45:19
in the space of a thousand years
00:45:22
punishing drought alternated with storms
00:45:24
and
00:45:25
monsoons River and forests sprang up
00:45:29
then turned to dry grassland All In The
00:45:32
evolutionary blink of an eye so we have
00:45:35
a complete change of our ideas from this
00:45:37
slow drying out to this incredible
00:45:40
change between wet and dry wet and
00:45:43
dry what effect did that have on our
00:45:46
ancestors could these periods of climate
00:45:49
instability be the key to understanding
00:45:51
The evolutionary leap from small bipedal
00:45:55
Apes to the larger brain toolmaker Homo
00:46:01
habilis to know that scientists needed a
00:46:05
detailed record that went back further
00:46:07
than the
00:46:08
datom way back to the time when Homo
00:46:11
habilis was evolving 2 million years ago
00:46:15
that's only found in one place under the
00:46:20
ocean layers of deep sea sentiment tell
00:46:23
a story that goes back millions of years
00:46:26
they have to be drilled from the ocean
00:46:32
floor at his laboratory in Upstate New
00:46:35
York Peter Dominico keeps thousands of
00:46:38
columns of sand silt and rock a library
00:46:41
of ocean
00:46:45
cores one of the really attractive
00:46:48
features about ocean sediments is that
00:46:50
they accumulate very slowly but very
00:46:53
gradually and continuously over time
00:46:57
[Music]
00:46:58
each 3-ft Long Core holds a continuous
00:47:01
record of dust carried on the Wind from
00:47:03
Africa into the ocean where it now sits
00:47:06
on the
00:47:08
bottom nice there you go wow sweet okay
00:47:11
an expert eye can detect distinct layers
00:47:14
thick in dry years when the dust is
00:47:16
easily picked up by the wind thin in wet
00:47:21
years by measuring the layers they can
00:47:25
tell when the climate was wet or dry so
00:47:28
we can read these deep sea sediments
00:47:31
almost like an earth history book of
00:47:33
past changes in climate to make sense of
00:47:36
all this dirt they have to know when it
00:47:38
blew into the
00:47:39
ocean they can do this by dating the
00:47:42
shells of tiny sea creatures that sank
00:47:45
to the bottom at the same
00:47:48
time so this gives us an age the other
00:47:51
analysis gives us the
00:47:52
climate nice peter took this finely
00:47:55
detailed climate diary and compared it
00:47:58
to the Grand Arc of our human
00:48:02
evolution for the 3 million years
00:48:04
between tumai and Salam when brain size
00:48:07
was
00:48:08
flatlining African climate was stable
00:48:12
dry getting a little
00:48:14
drier then came 200,000 years of wildly
00:48:18
varying climate careening unpredictably
00:48:21
between wet and
00:48:25
dry during that time stone tools
00:48:28
appeared along with the larger brained
00:48:30
creatures that made them Africa was also
00:48:34
home to many other humanlike species
00:48:37
climate instability put pressure on all
00:48:40
of them so there are these time periods
00:48:42
when African climate was really unstable
00:48:44
so anything that was living there at the
00:48:46
time would have had to adapt to really
00:48:47
dramatically different climate
00:48:49
changes those that couldn't adapt died
00:48:52
out like Salam and Lucy's
00:48:55
kind better problem solvers like Homo
00:48:58
habilis
00:49:00
[Music]
00:49:04
survived the new discoveries about
00:49:07
ancient climate upheavals in Africa have
00:49:09
led Rick Potts to formulate a bold
00:49:12
theory of human
00:49:16
evolution the traditional idea we have
00:49:18
had about human evolution is that it was
00:49:21
the Savannah the grassy plane with some
00:49:23
trees on it that was the driving force
00:49:26
but but instead what we've discovered is
00:49:28
that climate changed all the time and so
00:49:32
the idea that we've come up with is that
00:49:34
variability itself was the driving force
00:49:37
of human evolution and that our
00:49:39
ancestors were adapted to change
00:49:45
itself it's a simple but revolutionary
00:49:48
idea human evolution is Nature's
00:49:51
experiment with
00:49:53
versatility we're not adapted to any one
00:49:56
environment or climate but to many we
00:50:00
are creatures of climate
00:50:03
change I think we should actually look
00:50:05
to our proud ancestry and how we evolved
00:50:07
in East Africa and say that's how we
00:50:09
survive that we can survive the future
00:50:12
because we are that creature because we
00:50:14
are that
00:50:17
smart today climate change seems to
00:50:21
threaten our
00:50:23
survival but it may have held the keys
00:50:26
to the the astonishing story of how we
00:50:29
became who we
00:50:30
are because it didn't stop 2 million
00:50:33
years
00:50:35
ago these dramatic upheavals would
00:50:37
continue for another million and a half
00:50:42
years propelling our ancestors down a
00:50:45
road leading ultimately to the smartest
00:50:48
creature the world has ever known
00:51:01
Nova's got a brand new Evolution website
00:51:04
with lots to explore about our ancestors
00:51:07
we want to know what you think bookmark
00:51:09
it today and give us your feedback find
00:51:11
it at
00:51:15
pbs.org a mystery Unearthed a nearly
00:51:19
complete skeleton this is a big strong
00:51:21
creature the first species that looks
00:51:23
like us looks like us and surprisingly
00:51:26
is like us nearly 2 million years ago
00:51:30
now meet him face to face a
00:51:33
groundbreaking Nova special tells a new
00:51:36
story of human evolution our story part
00:51:40
two of becoming human birth of humanity
00:51:43
next time on Nova
00:51:53
[Music]
00:52:07
this Nova program is available on DVD
00:52:10
and Blu-ray at shop
00:52:12
pbs.org or call 1800 play PBS
00:52:18
[Music]
00:52:25
[Music]
00:52:35
[Music]
