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00:00The vast continent of Africa stretches toward an infinite horizon.
00:16For more than five million years, life has thrived in this landscape of extremes.
00:24And it is here that the search for man's origins began.
00:30One of the oldest known signs of our arrival are hominid imprints dating back three-and-a-half million years.
00:45Indelibly set in stone, these age-old footsteps point the way toward our future.
00:52Though much about our lineage remains a mystery, scientists believe that humans evolved from primates, perhaps the apes that once lived in southern Africa.
01:08The day our ancestors learned to walk upright was an evolutionary milestone.
01:18Their striding gait on two legs, an adaptation that would define their place in history and set them apart from every other living creature.
01:34Another living creature.
01:35The End
01:39¶¶
02:08¶¶
02:38For more than 100 million years, dinosaurs ruled planet Earth,
02:56exploiting habitats in every corner of the globe.
02:59¶¶
03:01But 65 million years ago, their long reign would come to an end.
03:09Hurtling through the atmosphere, an asteroid six miles wide struck the Earth with the force of 100 million megatons.
03:17In the wake of this cosmic collision, the planet appeared lifeless.
03:27But insects, plants, and some small mammals would survive and repopulate the landscape.
03:34This is Purgatorius, one of Earth's oldest primates.
03:44It was an arboreal animal, climbing trees to forage for fruit and insects.
03:52Modern primates may have evolved from creatures like this one.
03:56In the era after the dinosaur, the Earth regained its life force, and vast tropical rainforests stood watch over the continent.
04:14For hundreds of generations, this lush habitat would nurture new families of primates.
04:21Life thrived in the canopy, where food was plentiful and predators few.
04:33From the treetops to the forest floor, ecological niches were filled by a diversity of primates.
04:54These sumptuous forests may have helped to shape humankind's direct ancestors.
04:58Lake Victoria in Kenya.
05:05Within its boundaries lies a small island called Rusinga.
05:11Over decades, this site has yielded remarkable evidence of human origins,
05:18including the partial skeleton of a distant relative dating back 16 million years.
05:24Discovered by a team led by Mary Leakey, Proconsul is the earliest known ape.
05:35No other fossil ancestor has been reconstructed in such detail.
05:43Proconsuls may have climbed trees on all fours.
05:46With their long fingers, they could grasp the branches firmly with fore or hind limbs.
05:57A peculiar feature of Proconsul's teeth was scientifically noteworthy.
06:03Five raised bumps on the broad surface of the molar.
06:06This adaptation, unique to anthropoids such as chimpanzees, is also shared by humans.
06:19Its larger brain and lack of tail further reinforced the theory
06:24that Proconsul was a primate related to humans.
06:27But despite years of fossil analysis and ongoing scientific inquiry,
06:34it is not yet possible to name all the limbs of the human family tree.
06:39That human beings evolved from apes is a commonly held notion today.
06:55But when the idea was introduced back in the 19th century, it was pure scandal.
07:12In 1859, Charles Darwin published The Origin of Species,
07:16a fiercely debated work that outlined why the plant and animal kingdoms
07:22have so many diverse, yet similar species.
07:28The theory of natural selection was based on the idea
07:32that over time, only the fittest life forms survive,
07:37passing on their strengths to generations that follow.
07:40Twelve years later, Darwin would ponder human origins,
07:47but could not yet establish a clear-cut link between apes and modern man.
07:54In Darwinian circles, there was speculation about the animal that might bridge the gap.
08:01Illustrated here, this imaginary creature was named Pithocanthropus.
08:06The search began in earnest for evidence of the so-called missing link
08:13between humans and our primate ancestors.
08:18Come the turn of the century, fossils of a hominid were found on the island of Java, Indonesia.
08:25Commonly called Java Man, we know this fossil today as Homo erectus,
08:32a man-like ape that lived less than a million years ago.
08:36In the 1930s, the fossils of Peking Man were uncovered in China.
08:46Judging from the shape of their skulls and teeth,
08:53both Java Man and Peking Man looked more like humans than the ancient apes.
08:59Most paleontologists considered the size of the skull the dividing line between apes and humans.
09:13The missing link would be an ape-like creature with a larger brain.
09:17Hadar, Ethiopia, in East Africa's Great Rift Valley.
09:31This deceptively barren region boasts one of the richest fossil records on Earth.
09:40In 1974, a single specimen unearthed here would yield exciting new information about man's evolutionary past.
09:53In this unforgiving landscape, a joint French-American excavation team would find what they'd been seeking for three years,
10:03a partial skeleton of what was then the oldest known hominid, nicknamed Lucy.
10:15Formerly called Australopithecus afarensis, she is some three million years old with a small brain about the size of a chimpanzee's.
10:27Lucy's small skeleton had ape-like features, strong jutting jaws, long arms and short legs.
10:40But this Australopithecine had a feature unique to hominids.
10:46She walked on two legs.
10:57Professor Randall Sussman of the State University of New York Stony Brook has been studying Lucy's anatomy.
11:06He says that survival in Africa's changing landscape required extraordinary physical adaptations.
11:17Dr. Sussman's tests compare Lucy's bones and musculature with those of modern humans and apes.
11:24The ancient bones revealed that Lucy would have been capable of walking upright on two feet.
11:35Of special note was the shape of her pelvis.
11:46Lucy's hips were wide to support the weight of her internal organs when she stood.
11:54In contrast, the pelvis of quadrupeds like chimpanzees is long and narrow.
12:07Within the spectrum of primates, Lucy's pelvis is more human than ape-like.
12:16From the hip joint, the thighs slant inward from the waist toward the knees.
12:21This structure would permit stronger legs that could carry more weight,
12:28lowering the body's center of gravity and making an upright posture easier to hold.
12:34The enlargement of the brain and intelligence was not the first thing in human evolution.
12:44The first thing in human evolution was instead walking on two legs.
12:48Bipedality, or bipedalism as we call it.
12:51Bi for two and pedalism for walking on two feet.
12:54So, walking on two legs then is seen very clearly in Australopithecus apharensis.
13:01But at the same time, Lucy and Australopithecus apharensis in general had fairly small, almost ape-like brains.
13:08And in fact, many other aspects of their skeleton are very primitive as well.
13:12So, we now have a different conception of what sparked the divergence of apes and humans.
13:19And it was walking on the ground on two legs.
13:23Lucy, the ancient biped, stood less than three and a half feet tall
13:29and looked a lot like the modern pygmy chimpanzee.
13:31But she walked upright with a gait not unlike our own.
13:42Her discovery was undoubtedly a turning point in man's quest to understand his origins.
13:47Ancient theaters of evolution.
13:59Africa's forests are man's primeval home.
14:03They are constant custodians of life.
14:07And the only place on earth that still harbors our nearest kin.
14:11These ecosystems, in turn, are preserved by the complex interactions of their inhabitants.
14:22With an arboreal design and intelligence, the first ape-like primate, Proconsul, was well adapted to life in the forest.
14:38Its descendants, among them chimps, gorillas, and man, still find sanctuary in his shadow.
14:54These are chimpanzees, the most human-like apes, sharing nearly 97% of our DNA.
15:01Molecular evidence suggests that chimps are more closely related to humans than to gorillas.
15:15Humans may look, sound, and behave differently from apes.
15:20But all of our differences lie in a narrow 3% gene pool.
15:24In the remote forests of central Zaire, lives another distant relation.
15:27In the remote forests of central Zaire, lives another distant relation.
15:44Little is known about the bonobo, or pygmy chimpanzee, identified as a species less than a century ago.
16:04Here in the forest, bonobos, a matriarchal society, rely on each other for food, protection against their enemies, and even emotional support.
16:23Among the higher orders of primates, bonding has increased the chances of survival.
16:36In many, sometimes startling ways, this society of primates bears an uncanny resemblance to our own.
16:46Bonobos can walk upright, unlike any of the other great apes.
16:54Intelligent creatures with a large vocabulary of vocalizations and body language, they are extremely social.
17:03And like humans and chimpanzees, they can be affectionate, finding comfort in the warmth of their friendships.
17:11At the State University of New York, Stony Brook, researchers are observing chimpanzees in motion.
17:24The goal? To find out how early hominids came to walk upright.
17:28Watching the chimps in action, they will try to determine what each muscle group actually does.
17:45Flexing, rotating, and contracting.
17:48The complex muscles attached to the pelvis and thigh bone are carefully tested with the help of electrodes.
17:54This exercise shows that the gluteus medius, a muscle at the waist, is essential for controlling the tilt of the pelvis.
18:11The same holds true for human anatomy.
18:14When we lift a foot to take a step, the pelvis tilts in the direction of the raised leg.
18:21The gluteus medius of the opposite side then contracts to stabilize the pelvis.
18:32Without this muscle, the sway of the body would throw us off balance as we tried to move forward.
18:37The action of the gluteus medius is examined in active chimpanzees.
18:48When the chimp walks on all fours, the muscle barely moves.
19:01But when it climbs a tree, the muscle activates.
19:19Sussman and his colleagues were surprised to find that the gluteus medius serves the same function in both chimp and human anatomy.
19:29Rotating the thigh and maintaining the balance of the pelvis.
19:35But in each species, it plays a different role.
19:39In humans, the muscle permits a long-legged stride.
19:44In chimpanzees, a range of vertical motion with bent legs.
19:49With similar musculature in our pelvic areas, it's surprising that chimps became efficient climbers that didn't walk,
20:04while humans became successful bipeds.
20:06But as the dynamic in the forest changed and apes spent more time on the ground,
20:12the anatomy first developed to climb trees gradually allowed some primates to become proficient on two feet.
20:19Swinging through the treetops, heavier apes, like the chimpanzee, found that brachiating was a more efficient form of locomotion.
20:33Too large to scamper over higher branches, they would adapt both anatomy and behavior.
20:47We are the only animals that walk habitually on two lower limbs in a terrestrial niche on the ground,
20:58and that's the major hallmark of our locomotion.
21:02Now, there's many other subtle aspects of our bipedality that make us very efficient and able to walk over long distances without becoming tired.
21:13We sacrifice speed and we sacrifice some of the agility of the, say, African apes, our closest relatives,
21:23who can scramble up a tree when danger threatens or can scramble up a tree to get food and then come to the ground at other times.
21:31But bipedality, for reasons that we are not even sure today, bipedality conferred a selective advantage on early hominids
21:39about four to five million years ago, and walking on two legs became the fashion, became the hallmark of our species.
21:51To this day, the cause of this biological rift between the African apes and humans remains unknown.
21:59With few fossils to go on, solving the mystery of what transpired when humans and apes parted ways has challenged researchers across the globe.
22:11Dr. Satoshi Horai of Japan's National Institute of Genetics compares genetic maps in search of clues.
22:25Dr. Satoshi Horai found that as the number of generations increase, so do the number of genes that differ in animals that branched off from our primate ancestors.
22:40According to Horai, a detailed examination of these differences can pinpoint when humans and chimpanzees split from their common lineage.
23:02We've estimated when humans and chimpanzees split off from one another.
23:08The figure is about 4.9 million years ago.
23:13This number is based on the total base sequence, so the margin of error is just about 200,000 years, which is an extremely small margin.
23:23So we think it's fair to say that they branched out about 5 million years ago.
23:28Long after their split from apes like the orangutan and gorilla, both hominids and chimpanzees had followed the same evolutionary roadmap.
23:43But their paths may have diverged in the wake of a change some 5 million years ago.
23:52For more than 10 million years, major tectonic activity had shaken the continent.
24:01A cataclysm of heroic scale that transformed the African forests.
24:19Volcanoes erupted everywhere, and the terrain of East Africa rose almost two miles higher.
24:28Waves of molten energy from the Earth's core surged toward the surface.
24:35The shock created a 3,500-mile fracture along the edge of the African continental plate, from present-day Ethiopia south to Mozambique.
24:47This barrage of tectonic energy dramatically altered the East African landscape, which until then had been blanketed by rainforest.
25:10Steep, volcanic mountain ranges began to form along the length of the fault.
25:15Highlands rose, lowlands fell, and huge new lakes formed in what is now known as the Great Rift Valley.
25:34The Collège de France in Paris.
25:37Home base for Yves Coppon, a paleoanthropologist associated with the Lucy excavation.
25:46He believes that geological forces are primarily responsible for the differing paths of hominids and chimpanzees.
25:54The fault itself was not a barrier, but the wall these mountains presented effectively became one.
26:07It prevented hominids on one side and chimps on the other from making the trip across and back.
26:13I think that all of these populations formed only one community, with common ancestors somewhere in the range of 8 to 10 million years ago.
26:23And that the population became separated.
26:34The appearance of this huge natural barrier had many consequences.
26:39It may have altered the fates of several species and changed the face of the East African landscape.
26:54In the years before it existed, the continent's tropical forests thrived on abundant rainfall, blown in on westerly winds.
27:02Later, Dr. Coppon believes that the mountains cooled the air, shifting moisture away from the range's eastern slopes.
27:21But the rainfall was the lifeline for Africa's tropical forests.
27:25And dwindling precipitation eventually caused major changes in the ecosystem as forests gave way to savannah.
27:38Though no record of their presence exists, the ancestors shared by hominids and chimpanzees were clearly tree dwellers who had prospered in the once lush forests.
27:49Now, they would have to adapt or perish.
28:00These new environmental pressures triggered the changes that led to human evolution.
28:06Long ago, one of man's oldest hominid ancestors may have made her home to the east of this rugged Ethiopian range.
28:24But the present-day landscape offers few clues about the ecosystem of her day.
28:28What is known is that volcanic rock from the site where Lucy was found contained the pollen of three million-year-old plants.
28:42Professor Ramon Bonfi of the University of Marseille, France is hoping that pollen analysis will provide further insights into Lucy's habitat.
29:02A huge amount of rice pollen had emerged from the rock, along with that of a number of trees.
29:08With Africa's tropical forests on the decline, new vegetation, such as rice plants, were thriving in these grasslands, where rainfall was plentiful, but seasonal.
29:23For many creatures, survival meant adapting to a new habitat and diet.
29:28Lucy and other australopithecines must have ventured out of the forest to explore life in the wide-open savannah.
29:42And to the east, between the rift and the Indian Ocean, the forest was declining little by little.
30:01Replacing it, during the first phase of the decline, were a patchwork of smaller forests and savannah.
30:08There were still forests where hominids walked and also climbed.
30:15In the second phase, where the terrain was drier, they walked but no longer climbed.
30:23March, but no more climb.
30:35These miles of grassland have become Earth's most fertile hunting grounds for fossils of our hominid past.
30:42As the forests faded, the animals that remained soon learned that food was more difficult to come by.
31:00Although no one knows for sure why our ancestors became bipedal, new strategies for foraging may have provided the impetus.
31:20Negotiating the vast African plains would be an evolutionary challenge.
31:33With greater distances to travel between food sources, hominids required a more efficient means of locomotion.
31:40Walking upright was the bold solution.
31:50So different was this evolutionary adaptation that many experts consider it the turning point when the hominid line parted ways with the apes.
31:59Mahale, on Lake Tanganyika, Tanzania.
32:17The area is nestled in the western side of the mountains, where deep forests remain.
32:23The region is a haven for chimpanzees, our closest living relatives.
32:31Creatures that did not habituate to walking on two legs.
32:39Exploring new and sometimes dangerous territory, our common ancestors may have become bipedal as the need for protection and defense became greater.
32:53In the bountiful forests of the western divide, life probably continued much like it had for millions of years.
33:03Dr. Coppon believes that the animals which remain tree dwellers are related to modern day chimpanzees.
33:10Chimps had great potential as bipeds, had circumstances allowed, but then life might have taken a different twist.
33:24One could say, in any case, from what we know now, that if Equatorial Africa had remained completely forested, we would still be apes adapted to that forest, swinging happily in the trees.
33:45As the planet stirred anew, our ancestral forests vanished into history.
33:56In the aftermath, the next act in the evolution of humankind would unfold.
34:03Unsuspecting players in an age-old drama, apes would thrive on either side of Africa's great divide, their fate sealed by an accident of geography.
34:17The savanna posed new challenges for hominids that had evolved from forest dwellers.
34:28Here, walking upright had its advantages.
34:33Among them, the use of the arms to carry loads and the ability to spot danger in exposed terrain.
34:40Miles of sun-parched landscape were the domain of a diverse and ferocious group of predators.
34:52And there were few places to hide when they were on the attack.
34:59To avoid sharing their kill with intruders, leopards muscled them up a tree.
35:04Rare specimens from these hunts can be found in South Africa, bones that tumbled into a cave and fossilized.
35:22Deer and rabbit are among the most common fossilized remains here.
35:28But evidence of a new man-ape was also recovered.
35:32The fossils of Paranthropus robustus, or robust almost man.
35:39A hominid that appeared two million years after Lucy.
35:45In the back of its skull were two enormous puncture marks.
35:49The holes are a perfect match with the fangs of a leopard's jaw from that era.
35:54Even solidly built hominids, like this one, were not immune from attack.
36:07The size and shape of the brain somewhat resemble a gorilla's, and weigh about the same as Lucy's, just over a pound.
36:21But other features of the skull are more human-looking.
36:24Alongside the ancient hominid, paleontologists recovered artifacts never seen in Lucy's era.
36:41Stone tools.
36:47The accepted theory is that only after the brain had enlarged and intelligence developed,
36:57could hominids fashion tools out of stone.
36:59But with its still primitive-sized brain, was Paranthropus robustus a toolmaker?
37:08For Dr. Sussman, the answer may not lie with the brain, but in the anatomy of the hands.
37:15Animals that have this metacarpal head and these added muscles that we find in humans,
37:27and presumably in these early human ancestors,
37:30these animals are able to do what humans and presumably our early ancestors could do,
37:36namely pick up an object between the thumb and the fingers,
37:40pick up an object with a refined precision grasp.
37:43Chimpanzees and gorillas, when they similarly grasp small objects,
37:49they grasp them between the edge of the thumb and the side of the index finger,
37:56in a very less effective precision-type grasp.
38:00So chimpanzees and gorillas pick up small objects like this.
38:04Humans, and presumably our early ancestors who had these additional muscles,
38:09pick up small objects, not like a chimpanzee, but in a more advanced precision way,
38:17where the thumb is opposed to the other fingers.
38:21So here we have an ape-type precision grasp, and here we have a human-type precision grasp.
38:26They're very different, and the two types of grasp reflect this primitive morphology,
38:31in the case of a chimpanzee, and the more advanced morphology in the case of a modern human or a human ancestor.
38:41This is the hand of Paranthropus robustus.
38:53Like a modern human's, his thumb bone is thick, indicating well-developed muscles.
39:00It is also splayed.
39:01These signs tell Sussman that tool-making was within reach.
39:12To pick up a small object, humans use the tips of our thumbs and forefingers.
39:20Though we do it unconsciously, this movement requires precise control.
39:25With long, slender hands and a narrow thumb, it's doubtful that Lucy's family were tool-makers,
39:38though they may have used them.
39:43Their bones look more like chimpanzees than modern humans.
39:46The chimpanzees' thumbs are disproportionately short and thinner than their fingers,
40:03with very little muscle tone.
40:11With hands like hooks, chimpanzees are not dexterous enough with their thumbs
40:15to retrieve and manipulate small objects.
40:19And it's likely that Lucy fared no better.
40:28Dr. Sussman believes that with the evolution of fully opposable thumbs,
40:34Paranthropus robustus became one of the planet's first tool-makers.
40:38Lucy's arrival three million years ago marked a turning point in history.
40:51No longer dependent on forelimbs for walking or swinging through the treetops,
40:56our hominid ancestors used their hands to gather food, work with tools,
41:01and perhaps even to communicate with others.
41:05Over the course of millennia, the bipeds of Africa's great savannahs became highly proficient walkers.
41:19About a million years after the appearance of Paranthropus robustus,
41:29another hominid had climbed a rung on the evolutionary ladder.
41:33Its fossils were recovered in 1984 from Lake Turkana in northern Kenya.
41:41At just under six feet, Homo erectus was tall and long-legged,
41:48with a physique and striding gait resembling modern humans.
41:52More than two million years after the emergence of the planet's first hominids,
42:01our ancestors walked much like we do today.
42:07Standing erect led to another pivotal evolutionary change,
42:12the ability to speak.
42:13Earlier hominids, like Lucy, had walked with a slight stoop.
42:22With narrow throats and larynxes constricted by their posture,
42:28they could not produce the complex sounds that compose human speech today.
42:34When Homo erectus stood up straight,
42:38his vocal cords had much more room to reverberate sound.
42:52This anatomical adaptation would open a new avenue of verbal communication
42:58that would revolutionize human development.
43:01With double the brain weight of his older cousin Lucy,
43:09Homo erectus was undoubtedly a more intelligent being.
43:13But his capacity did not yet match the level of humankind today.
43:21It would take another million years for modern man to evolve.
43:24Intelligent beings like early Homo sapiens formed complex societies,
43:35produced art and sophisticated tools,
43:38and spoke a language.
43:42They now had the power to shape their future.
43:44Three million years ago, Lucy, the planet's first biped,
43:55began the long march toward civilization,
43:58relinquishing her niche in the forest of her birth.
44:06Today, humankind's success as a species
44:09is no longer a simple matter of physical design.
44:13The development of a brain that can convey information,
44:17organize a defense, create art, and invent the wheel
44:22is challenging age-old patterns of evolution.
44:25For millions of years, all manner of life took sanctuary
44:40in the great forests of Africa.
44:46They include the higher mammals,
44:49the families of intelligent primates
44:51to which we humans may owe our ancestry.
44:55When the Earth shuddered,
45:02forcing early hominids to explore new terrain,
45:06the changes would reverberate over thousands of generations.
45:13Random acts of nature,
45:16turning man-like apes into ape-like men.
45:20And finally, into Homo sapiens,
45:22the wise human with the daunting task of living up to its name.
45:25with the daunting task of living up to its name.
45:28of Homo sapiens,
45:29the wise human with the
45:58ORGAN PLAYS
46:28ORGAN PLAYS
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