"Africa, two million years before your time, and life on Earth has a brand-new face." "First, our ancestors walked on two legs, and stood out from all other animals." "Now we'll meet creatures who took the next vital step from ancient apes to us creatures perhaps like him." "I'm travelling back in time." "With science, we can build a picture of our past and bring our dead ancestors to life." "Join me on a journey through our human story." "We've arrived at a critical moment in our story - a crossroads in our evolution." "I'm right here, where there's not just one species of apeman on the savanna, but several, and one of them could be our ancient ancestor - but which?" "Meet Paranthropus boisei - boisei for short." "You know, you can sometimes discover an enormous amount about how a species behaves from just one or two simple observations, and these boisei are no exception." "If you had to pick one species from modern times - from the 21st century - that they remind me of, it would be the gorilla." "This is a full-grown adult male." "And this an adult female." "He's taller than her at around four and a half feet, and he weighs nearly twice as much." "This difference tells us about how they live." "He's the dominant male of his troop." "His sheer bulk and power holds the rest together, and he alone mates with all the females." "And she's not just any female - she's the most senior in his harem." "But that position could be under threat." "It's a young female, looking for a new troop to join." "But a stranger, with their capacity to upset the balance of power, is always a disturbing sight for a settled troop of apes." "(GRUNTS AND SHRIEKS)" "To win herself a place in the group, the newcomer must be accepted by both the dominant male and to an extent, the other females." "Whatever the potential for trouble, the dominant male is already interested." "He seems keen to add to his harem, whatever the consequences." "(GRUNTS)" "By piecing together what we know about these creatures from the bones they will one day leave behind, modern scientists think they have an idea of the part they play in the evolution of you and me." "But by being here in East Africa two million years ago, we can also do something else." "We can actually see for ourselves the everyday lives of individual apemen, and we can discover what it is about them which lives on in us." "And to do that, we're going to need to follow the lives of more than just one type of apeman, the boisei." "(SHRIEKING)" "We're also going to have to take a close look at apemen like these " "Homo habilis." "They don't remind me of anything alive in the 21st century." "The Africa of two million years ago is one of the most diverse habitats on Earth, with creatures both familiar and strange." "Dinofelis, the False Sabre Tooth." "The giant elephant-like Deinotherium." "The browsing ancylotherium." "And unlike anything we can imagine in the 21st century, there are the many two-legged apemen." "There's the habilis - impish scavengers." "Rudolfensis - their slightly bigger rivals." "The gorilla-like boisei." "A whole range of upright apes." "Each of them has a different strategy for survival, and from one, we've inherited our own way of life." "The question is which one?" "Who do you most recognize in yourself?" "Which one is our ape ancestor?" "To find out, we must first ask why there are so many to choose from." "Why, two million years ago, do we find so many different apemen?" "Well, one explanation lies not on Earth but in space." "It turns out that it's all the fault of the sun." "As the earth orbits the sun, it's always on a slight angle, a tilt." "It's this that gives us our seasons." "The bigger the tilt, the more severe they'll be." "But the tilt is always changing, and around three million years before the 21st century, it was getting bigger." "On Earth, the summers got colder." "At the poles, ice made during the winter didn't melt properly during the summer." "Year by year, the polar ice caps grew." "They locked up huge amounts of the planet's water." "The earth began to dry out." "In East Africa, vast areas of rainforest and woodland died off, leaving a hotchpotch of scattered trees." "And an alien species took hold." "It's grass." "And with alien plants came alien animals with bizarre adaptations to exploit the new foods, like the improbable four stomachs of an eland that can digest tough grass like a cow does." "And new animals create new food, and new creatures have evolved to eat it." "And this is the key to the puzzle of why there's so much diversity of apemen species at this time, two million years before the 21st century." "Africa now offers an incredible variety of things to eat and ways to live, and all kinds of animals have evolved to live here from the ancylotherium to our apemen." "Take these reeds, for example." "I can't eat this kind of food, but there is a species of apeman here that can the boisei." "These magnificent creatures are adapted brilliantly to make the most of the foods that surround them." "Powerful muscles in their cheeks, an enormous jaw and back teeth four times the size of our own, means they can eat the toughest vegetation like the roots of these reeds." "Their specialisms make the boisei incredibly successful." "We're months into an exceptionally long dry season, and many animals are finding the going hard, but for this troop, the pickings are easy." "With ample food within easy reach, there's plenty of time for any apeman's favourite pastime - sex." "The new female is still hovering around the troop, waiting for a chance to get close to the dominant male." "For the existing queen of the harem, the newcomer could be a real threat." "(FEMALE SHRIEKS)" "(MALE GRUNTS)" "But the dominant male has a simpler view - a new female isn't a threat, but a challenge." "Although almost entirely vegetarian, we know from tell-tale signs in their teeth that there's one kind of meat a boisei can't resist " "termites." "Doubly irresistible when on the menu of a romantic meal for two!" "Grooming is how all apes bond with each other, and the boisei are no exception." "The newcomer has become a new favourite." "But whether she'll prove as popular with the rest of the troop remains to be seen." "If the boisei lead comfortable lives with mostly domestic concerns how are the other local apemen faring?" "The Homo habilis we met earlier are finding the long dry season considerably tougher than their boisei neighbours." "This is the habilis dominant male, and he's found a bee's nest." "His position as leader depends mainly on his ability to find food." "Though tricky to get at, and not really offering much of a meal, desperation has forced him to try a raid." "That's one of the females the dominant male mates with." "She'll stick with him for now, but unless the troop finds food soon, it will begin to break up." "This is our cheeky friend who attacked the car, eating his first meal for days." "The truth is, the habilis are struggling, and there's a simple reason why." "They don't have the special adaptations of the boisei, and without big teeth and powerful jaws, the habilis can't live off the kind of tough vegetation seen at the end of a dry season." "A boisei speciality like reed roots or this hardened acacia pod, isn't exactly on their menu." "To make up for their lack of specialist eating equipment, habilis have taken a very different tack." "They've developed into the archetypal Jack-of-all-trades." "Inquisitive scavengers, prepared to try anything to survive!" "But it's a difficult way to live, because while the boisei know where to find their food, a meal for habilis could be anywhere." "To find it, you need to be a tireless investigator." "But simply being inquisitive is no guarantee you're going to find a square meal." "You also need a bit of luck..." "Oi, you!" "(SHRIEKS)" "And good luck is something that this troop hasn't had much of recently." "In fact, the troop's plight is desperate but their inquisitive way of life has given habilis a few tricks, because if you're inquisitive, you investigate mysteries... like why do vultures gather together?" "The answer, of course, is that they've spotted food." "An eland has been killed on the savanna." "The carcass is a godsend." "Not only is it food, it's valuable protein and animal fat." "Unlike the boisei, habilis eat meat." "Normally, the dominant male would approach a carcass warily, particularly one so fresh." "Whatever killed it could be still around." "Today, his hunger, and the troop's excitement, outweighs any caution, though the young male seems quite wary." "But other apemen have also spotted the vultures." "Habilis aren't the only scavengers around." "A rival species, rudolfensis, has also come for the meat." "(GRUNTING)" "Habilis and rudolfensis are remarkably similar, and are frequently driven to fight for food." "It's the dominant male's moment of triumph." "He's led his troop to food and thinks he's successfully defended it." "The troop are distraught." "Not only have they lost the valuable meat, they are now also leaderless." "With no obvious candidates to succeed the dominant male, the habilis have reached their lowest point." "The onset of rain brings relief across the savanna." "And hope that their luck may change." "The long dry season is at last at an end." "The onset of rain brings relief across the savanna." "(GRUNTS)" "The boisei sometimes display when it starts raining." "No one knows exactly why." "Perhaps it's out of sheer exhilaration or maybe they just hate getting wet, but it's common behaviour amongst apes in your own time." "And sadly for boisei, just like modern-day gorillas, they're useless at building shelters." "The boisei and the habilis embody two very different approaches to survival." "Habilis are the Jack-of-all-trades, the boisei the master of just one." "But which trait will be passed on to future apemen?" "What will we inherit in two million years' time?" "Although the boisei have a lifestyle which is incredibly successful, it's only a success as long as the world in which they live doesn't change, and if there's one thing you can bet on about the environment or the weather," "it's that nothing stays the same forever." "Let's take a glimpse at what's to come." "Over the next several hundred thousand years, the same forces which created the vast range of environments in Africa will continue to shape the continent." "New habitats will appear, along with new animals to exploit them, while old ways of life will die, and old species of animal with them." "Caught up in all this change, the boisei will find themselves in a world they're simply unprepared for." "But for the moment, all that lies hidden in their future." "The dominant male boisei rejoins his harem to find its number expanded by one." "The dominant female has taken the newcomer under her wing, and subtly shifted the balance of power." "He may well find that he has some making up to do." "Their successful way of life hides the fact that the boisei have put all their evolutionary eggs in one basket." "The trouble with being a specialist is that you end up getting left behind." "Perhaps they won't be able to adapt to vegetation changes, or new animals will make their lives difficult." "The truth is, were we to come back to this glade in a few hundred thousand years' time, these magnificent creatures, the boisei, would have gone." "The only legacy that these lovely animals will leave will be these - fossilized bones." "Nothing from these apemen will live on." "But the part that habilis plays in the story of you and I will be very different." "Now that the vultures have had their fill, there will be little meat left on the carcass for anyone else." "But the habilis have a secret weapon." "Their scavenging, inquisitive lifestyle has made them quick-witted and inventive, and it's led to a real breakthrough." "Habilis are the first creatures on Earth to be able to make stone tools." "It's a hugely important leap forward, for stone tools mean that they can live off an amazing range of different foods." "But first, they have to be able to get to them and that's where habilis's second secret weapon comes in." "Eating meat has brought habilis the essential protein and fat to allow the development of their brains." "In fact, habilis's brains are almost half as big again as those of the boisei." "In other words, meat has enabled them to grow smarter." "Smart enough to know that you stand more chance of scaring off a lion if you work as a team." "Welcome to the new world of ideas." "Although the eland carcass has almost been totally stripped of meat, there is one last meal left - bone marrow, one of the most nutritious foods on the savanna." "Neither lion nor vultures can reach it, yet habilis's new tools seem almost purpose-built for the job." "The troop may have also solved their leadership problem." "The young male's actions in getting food have given him a real status." "It seems likely that he will now take over as the dominant male." "Habilis' Jack-of-all-trades way of life means that they have a chance of surviving in an ever-changing world." "It's this trait that will live on and be essential in us." "So it's habilis which has taken the next step towards being you and I." "By being able to live in different ways instead of being trapped in just one, it's begun to free itself from the rules governing all other life on Earth." "Does this mean that it's habilis which will dominate Africa in millennia to come?" "You might think so." "But the end of our story has a strange twist." "Round about now, two million years ago, an apeman appears in East Africa which does what habilis does, only better." "But they have something else which means that they could end up hounding habilis out of existence." "They are called Homo ergaster and they are the creatures we're going to meet next on the journey from apes to us."