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00:34This is the story of how we are different to every other creature that's ever walked the earth.
00:43And the key to its telling lies with your family.
00:52Hmm.
00:55That's my mother when she was four. That's one generation ago.
01:00Look at the sulky face. She sulks just like I do now. She'd just run away from home.
01:05And there's my grandfather wearing his major's uniform.
01:09This would have been about 1916, the time of the First World War.
01:14And then over the page, we've got my grandmother with her mother, Julia.
01:18That's my great-grandmother.
01:20You see, that's three generations ago.
01:23But supposing we could go back not just one generation, or two generations, or even three generations, but 300 generations.
01:38To an ancestor who shared the world with the Neanderthals.
01:46Jump back 60,000 generations, and we'd meet one of the first people to ever set foot outside Africa.
01:56A hundred thousand generations, and meeting the relatives would be even more intimidating than you could ever have imagined.
02:04And that's just what we're going to do, travel through time, meeting the creatures who have become us, to see
02:11how their lives have led to the amazing reality of a house.
02:18Our dead ancestors have left us a key to unlock the past.
02:24With their fossil bones and relics as a guide,
02:29scientists could build up a picture of what it would be like to travel back in time.
02:43If all the ape-long fossils from all over the world were collected together,
02:47I could probably fit the whole lot in the back of this car.
02:55Yet each little fragment tells a tale about the world of which it was once a part.
03:01These tiny pieces hold secrets, not only to how our ancestors died, but to how they lived.
03:16From our closest cousins, the Neanderthals, to the first fierce Europeans.
03:30From our ancestors with the wit to survive in the jungles of Asia,
03:34from our ancestors with the wit to survive in the jungles of Asia,
03:35to the first true families who worked together in sun-baked Africa.
03:45We're journeying back in time, revealing with each step the secret ingredients that make you and me unique,
03:53and meeting the first creatures to have them.
03:57the earliest tool-makers,
04:00the heavyweight contenders who've shaped our past.
04:09Right back to see for ourselves how you and I came to be.
04:17The first clear place our fossil guide takes us is here.
04:22We've traveled three and a half million years into our past,
04:27as science sees it.
04:29To meet a creature who began the journey from ancient apes to us,
04:33in Africa, in this tree.
04:42This is your distant relative from 300,000 generations ago.
04:48Ostradopithecus afarensis.
04:50They're nesting for the night.
04:56This one has a special role in the story of you and me.
05:00We'll call her Lucy.
05:01Lucy. She's special to someone else as well,
05:04her infant, born just a few days ago.
05:09Lucy's troop is engaged in a turf war,
05:12a potentially violent territorial dispute.
05:15In the morning, it will change their lives forever.
05:52The afarensis, like apes of any time,
05:55filling up with water is an important mission of the morning.
06:11But there is something that sets these creatures apart
06:14from other apes.
06:16The first step on the journey to us.
06:27They can stand and walk on two legs.
06:33This is the troop's most senior male.
06:36He's also the father of Lucy's infant.
06:39He's 25 years old and in his prime.
06:42He could live as long as 50 years.
06:48That's Anselotherium, a cousin of the rhino.
06:55In this prehistoric world,
06:56it's the leader's strength that holds the troop together.
07:16But if you think standing on two legs
07:19makes our ancestors king of the jungle,
07:21then you're wrong.
07:29Aside from walking upright,
07:31there's really nothing very remarkable
07:33about these creatures at all.
07:35They're as subject to the laws of nature
07:37as everything else.
07:47Yet Lucy and her kind
07:49are the ancestors of you and me.
07:52To discover exactly what makes them so special,
07:55we must watch them rather more closely.
08:03Lucy is 22.
08:08She's mother not only to her new infant,
08:11but to several others in the troop,
08:13including this adolescent female.
08:20who also makes a handy babysitter.
08:31The sound is an unsettling one.
08:34It's a forensic, but a rival troop.
08:37Several times Lucy's troops' territory has been invaded
08:40in a battle for its rich pickings.
08:49Losing their leader presents another problem.
08:53Losing their leader presents another problem.
08:53Two males are contenders for the throne.
08:56He's the quiet man of the troop,
08:59dependable and solid.
09:01He's the quiet man of the troop.
09:02Whilst he is quite the opposite,
09:04brash and impulsive.
09:06Now they're driven to work together.
09:10A patrol party must be organized,
09:12and the males will rouse themselves
09:14into a frenzy of display to form one.
09:29An afferentis troop has a territory much like a modern chimps.
09:35Perhaps ten square miles, bounded by rivers and mountains.
09:47Although the adults know their way around well,
09:50a crossroads is a flashpoint for the leadership battle to begin.
09:55The first skirmishes are noisy displays.
10:03The eventual winner will gain respect
10:06and privileged access to the troops' females.
10:13Meanwhile, the rival troop is surprisingly close by.
10:24These reed beds form the overlap
10:27between the neighboring afferentis territories.
10:30Normally, neither troop comes here,
10:32as they're not a good place for fruits and food.
10:37But this group of intruder males are on the trail of something different.
10:47Lucy.
10:48Probably while foraging nearby, she's disturbed them.
10:53An isolated afferentis is always vulnerable.
10:57The intruder males will seek them out
10:59and attack them to warn off their troop.
11:02At just over a metre tall, a female like Lucy is an easy target.
11:15If they found her now, they'd almost certainly kill her.
11:35It's a lucky escape.
11:44With the trail cold, the intruder males move on.
11:51The river marks their southernmost borders with Lucy's troops' land.
11:57It also makes a handy refreshment stop.
12:05And not only for the intruders.
12:09By pure chance, the patrol party from Lucy's troop
12:13have also stopped by for a drink.
12:16As with rival apes of any time, the encounter provokes a face-off.
12:25With the water between them, actual bloodshed is unlikely.
12:29Instead, displays of noise and power are the order of the day.
12:34Which is lucky for Lucy's males, as the intruders have arrived in numbers.
12:44If they were to meet on different ground, one might see a pretty uneven fight.
12:53The more you watch these creatures, the more like apes they seem.
12:58So why, in the one crucial aspect, are they so very unlike apes?
13:03What on earth could have happened to make an ape stand upright and walk on two legs?
13:10Well, what happened is, the world changed.
13:18Come with me and travel even further back in time.
13:22Before even Afarensis was around.
13:27Four, five, six million years ago, and further still.
13:39We're still in Africa, but it's eight million years ago.
13:44And home to the tree-living ancestor of Lucy and her kind.
13:51We've never found any fossil evidence of these mysterious apes.
13:56Yet we know a few vital things about them.
14:15We know that, like the apes in modern times, these animals use both their hands,
14:20as well as their feet, to help them get around.
14:24We know that's true because it's the only way to get around in their dense forest home.
14:30And how do we know this forest is their home?
14:34Because this forest is everywhere.
14:41Eight million years ago, Africa is covered in thick forest, almost from edge to edge.
14:47And it's the forest, and what happens to it, that holds the secret to why an ancient tree-swinging
14:53ape was transformed into a two-footed Afarensis.
14:58The shift from creatures who move around on four limbs, to those that walk about on two,
15:04is so dramatic that it can only be achieved by an equally dramatic change in the world around them.
15:13And that change is being driven from thousands of miles away, deep beneath the sea.
15:24Here, the ocean floor is expanding.
15:30At about the speed that fingernails grow, the Earth itself is on the move.
15:38It's changing the face of the planet.
15:46A vast chunk of the Earth's crust has been pushed to the north.
15:51One day, we'll know it as India.
15:57Deep underground, as it collides with Asia, it creates a twisted mass of rock.
16:07Five miles high and 3,000 miles long, the Himalayas.
16:15The mountains are having an extraordinary effect on the world's weather.
16:20They've prompted some of the heaviest storms ever seen, the monsoons.
16:32The rains strip the air of moisture, so that the air currents that reach Africa are not wet, but dry.
16:44The rain forests retreat, and a new world is created.
16:49Over millions of years, a landscape of scattered trees take shape.
16:56And something else has changed the scenery.
17:03A vast chasm, the Great Rift Valley, has ripped down one side of Africa.
17:11Everything from beetles to apes, has had to keep pace with this incredible change.
17:20Our tree-swinging ancestors have evolved and transformed.
17:25Forced to spend more time on the ground, they've become the upright walking Afarensis we've met, like Lucy.
17:52But why use only two feet to get around on the ground?
17:55It's easy to think that being upright brings obvious advantages.
18:03Lucy can stand taller and see further.
18:10But that also means everything else can see her.
18:14It's a black eagle.
18:17An expert aerial hunter.
18:20An adult Afarensis is too big to take on.
18:24But where there are adults, there are infants.
18:27Can not possess.
18:27Oh boy.
18:30Oh, my God!
18:45Oh, my God!
18:46One, one, two, three!
19:01Two legs have, in fact, made Lucy neither quicker nor safer.
19:07So what is the advantage to Aferences of walking upright in this new world?
19:19The truth is, walking on two legs has become a defining feature of my life and yours for the most
19:26surprising of reasons.
19:29Ultimately, it's all about sex.
19:37The males have returned from their patrol. They must have tireded their face-off with the intruders.
19:47With security looked after, it's an opportunity for the troop to get about the serious business of grooming and building
19:54relationships.
19:59With Lucy's regular mate gone, she attracts immediate attention.
20:06It's one of the leadership contenders, a quiet one.
20:14In the natural world, sex and raising babies is the key to a species surviving.
20:24So that anything that gives you extra energy to do it better is like gold dust.
20:33And extra energy is what walking upright has given Aferences.
20:37In this mix of trees and grass, walking on two legs is simply more efficient for them than walking on
20:44four.
20:46The energy saved by changing from a four-legged way of life is tiny.
20:51The total number of calories saved by Aferences in a year is probably no more than that found in a
20:59packet of chocolate biscuits.
21:02But even such a tiny amount makes a difference.
21:10Lucy is able to recover that bit quicker after giving birth.
21:20It could mean, in a lifetime, she could raise just one more baby.
21:28And one more baby might be the difference between survival of the species and extinction.
21:44The rival troops are on the move again, this time from the west.
21:49And once again, patrolling takes priority.
21:56But not all the males are going to investigate.
22:00It's the brash would-be leader.
22:03He too has his eye on Lucy.
22:09All the attention is not simply to do with sex.
22:14To become the dominant male, he needs the support of the truth.
22:21And any chance to be alone with a high-ranking female like Lucy is not to be squandered.
22:36But his advances catch Lucy unawares.
22:40And his position between Lucy and her baby adds to her alarm.
22:47Suddenly, the situation is out of control.
22:50It's become a full-scale fight for leadership.
22:59The fight takes an unexpected twist.
23:02The brash contender grabs Lucy's infant.
23:05Whatever he hopes to achieve, the stakes are raised dangerously.
23:29It's the rival troop.
23:31They've come right into Lucy's troops' territory.
23:51With the new enemy surrounding them, the infant is instantly forgotten.
23:58Except, of course, by Lucy.
24:28This is my dream of Lucy's
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