NOVA examines a controversial theory that traces our ancestry to a small group of women living in Africa 300,000 years ago.
Category
📺
TVTranscript
00:00How much does this chimpanzee have in common with human beings?
00:10Scientists are trying to find out as they work to solve one of the most perplexing mysteries
00:14of all time.
00:16They are seeking out new clues in ancient fossils.
00:20And with experiments in ultraviolet exposure, they are attempting to recreate a time millions
00:24of years past.
00:27All these researchers are using the latest techniques that science offers as they hunt
00:31for the secrets of our human origins.
00:34As they search, they are arriving at some very startling conclusions.
00:39The group that gave rise to us, whether we call them anatomically modern humans, homo
00:44sapiens sapiens or whatever, that population contained a woman, an Eve if you want to call
00:50her that.
00:51And we're all descended from her.
00:53Tonight on NOVA, children of Eve.
01:06Major funding for NOVA is provided by this station and other public television stations
01:10nationwide.
01:13Additional funding was provided by the Johnson & Johnson family of companies, supplying health
01:18care products worldwide.
01:22And by Allied Signal, a technology leader in aerospace, electronics, automotive products
01:28and engineered materials.
01:52At this excavation site in Kenya, scientists are searching to discover the scattered remnants
02:01of a prehistoric people, our distant ancestors who might have roamed here hundreds of thousands
02:07of years ago.
02:10The tools they use are simple and the work is painstaking and tedious.
02:17So far, only a single fossil has been recovered for every million there must once have been.
02:24Although this record of human prehistory is sketchy, the search for these clues will continue
02:31as it has for generations.
02:34For many years, the scientists who study our origins have depended exclusively on the evidence
02:38found here in the earth.
02:41There were no other traces from our past to help them in their quest to answer the fundamental
02:45questions of humankind.
02:47Who are we and where have we come from?
02:51Questions that human beings have always asked.
02:54For much of our history, people believed that the world and all the creatures in it had
03:02arisen whole, complete and perfect.
03:06Man and woman, unique from the other animals, had been created in the image of a divine
03:11being, the children of a primordial Adam and Eve.
03:15In the middle of the last century, Charles Darwin shook forever this image of human beings
03:20and ignited a controversy that reverberates until today.
03:25Darwin observed creatures around the world and reasoned that a process of gradual evolution
03:30must be responsible for the great and grand variety of life on the planet.
03:36Since the beginning, he theorized, all species have undergone slow, progressive change, branching
03:41off from some common ancestor.
03:45He described a mechanism called natural selection, in which individuals better equipped to live
03:49in the environment survive while others perish.
03:56Society was outraged when Darwin stated that humans, like all other creatures, had evolved
04:00from more primitive species.
04:03People now took their place in the animal kingdom right next to the apes, with whom,
04:08Darwin said, we share a far distant cousin.
04:12Since then, scientists have looked to the only evidence available, the fossil record,
04:17for proof about our ancestors and information about when we separated from the other animals.
04:22On the basis of what they have gleaned from ancient bones, they've concluded that we diverged
04:27from the other primates and began the long march that brought us from apes to men and
04:31women about 20 million or so years ago.
04:36For decades, this date was considered inviolate, but recently it has undergone dramatic revision.
04:42Christopher Stringer, paleontologist at the British Museum.
04:46If you look at textbooks that were written maybe 10 years ago, perhaps even more recently
04:49than that, they usually paint a picture of us as being quite different from the apes
04:53and with a separate fossil ancestry that can be traced back to a split from the apes 15
04:59or maybe 20 million years ago, and on that basis we're not closely related to the apes.
05:04But the view that's coming through now very strongly, both from the molecular evidence
05:08and now from the fossil evidence as well, is that we are very closely related to the
05:12apes and especially to the African apes, the gorilla and the chimpanzee.
05:17When we look at our nearest animal relatives, we can see how much they resemble us.
05:22We all share certain body shapes, movements, and even behaviours.
05:28These similarities are largely determined by genes.
05:32Before we diverged from our common ancestor, humans and other primates had the same genes.
05:38As each species branched off, it began a process of change.
05:43This was the product of random mutations in our genes, which gives some individuals in
05:48a species the advantage over others.
05:51Natural selection preserves those mutations that provide a reproductive advantage.
05:55It is this process that fuels evolution.
05:59As time passed, these mutations accumulated, making each species more and more genetically
06:04different from its cousins.
06:10By the 1960s, new methods in biology were enabling researchers to use these differences
06:15in the genes to address the old question of our divergence.
06:20Two Berkeley scientists, Alan Wilson and Vince Sarich, were among the first to apply these
06:25new techniques to human evolution.
06:28Their work in 1967 sparked a decade of controversy.
06:33But what they did was surprisingly simple.
06:36They first collected samples of blood from human volunteers.
06:43They centrifuged the blood and extracted a protein called albumin.
06:47Like all proteins, albumin is determined by genes and therefore is an indicator of our
06:52genetic makeup.
06:57Then they produced antibodies to the albumin.
07:00To these antibodies, they added a small amount of the extracted blood protein.
07:05This caused a reaction between the antibodies and the albumin, which appeared as milkiness
07:09in the liquid.
07:13The human albumin to human antibody reaction was the strongest possible.
07:17When a chimp's albumin was added to the human antibodies, the reaction was weaker.
07:22Evolution had slightly changed the chimps' genes as reflected by their blood proteins.
07:27With baboons, the reaction was weaker still.
07:30This was evidence that evolution had made their blood very different from ours.
07:37Sarich and Wilson conducted similar comparisons between these three closely related species
07:42and other more distant species.
07:44They believed that these indirect comparisons of blood proteins, when quantified, could
07:49be used to determine how closely different species were related to one another.
07:54From fossil evidence, they knew that the baboon line had diverged from the human chimp line
07:59about 30 million years ago, and that the weak reaction between humans and baboons was the
08:04result of these 30 million years of genetic evolution.
08:08They theorized that by comparing this reaction with the human chimp reaction, they would
08:12have a direct measure of how long ago chimps and humans split.
08:17If as expected, the chimpanzees had diverged 20 million years ago, then their test tube
08:22should be almost as clear as the baboons'.
08:25Instead, it was very milky, in fact almost as milky as the humans'.
08:30And that meant that the chimp-human split belonged here, at about 5 million years.
08:36Sarich and Wilson announced that this was when we diverged from the chimpanzees.
08:41The reaction is pretty negative.
08:44If you read the textbooks of the period, and most textbooks published since then, there
08:49were either two, there were one of two responses.
08:51Either they ignored it completely, or they made a statement along the lines of Sarich
08:55and Wilson assumed constancy of rates.
08:58We know that no evolutionary systems evolve in a regular fashion, so we can reject it.
09:04These criticisms arose because Sarich's technique assumed that the random mutations upon which
09:09evolution depends occur at a steady rate over millions of years, like the ticking of
09:14a clock, a molecular clock.
09:18However, many believe that different species can evolve at dramatically different rates,
09:24and that this means that the rate at which genes change must also be very irregular.
09:29The molecular clock's tick was not steady enough to be relied on.
09:35David Pilbeam.
09:36They expressed their disbelief largely by saying that this couldn't possibly work, that
09:41it was well known that natural selection affected evolutionary rates greatly, and that it was
09:46impossible for evolutionary rates not to vary, so it simply was not on the cards that one
09:52could have a system that evolved at a constant rate.
09:56If a chimp, for example, had evolved more or less slowly than human beings, then the
10:00degree of genetic difference between them would not be a reliable indicator of their
10:04divergence.
10:06But Sarich proposed a way to prove his clock, a constancy of rates test.
10:12Sarich knew that the baboon line and the human chimp line had been evolving away from a common
10:16ancestor for the same amount of time.
10:19If the molecular clock was constant, the amount of genetic difference between chimps and baboons
10:24and humans and baboons would then have to be the same.
10:29Using blood protein analysis, he looked at the differences between the baboon and the
10:32chimpanzee and between the baboon and the human.
10:37In both cases, the amount of genetic difference was the same, and Sarich argued that chimps
10:42and humans had been evolving at a similar rate.
10:45Confirmation came after more tests between these and other more distantly related species.
10:50Sarich was confident his clock was reliable.
10:54Because the fossil record pointed to an older divergence state, for over a decade many scientists
10:59disregarded Sarich and Wilson's work.
11:02But by the 1980s, new fossil finds were lending support to the growing body of biological
11:07evidence for a more recent date.
11:10Sarich and Wilson worked with blood proteins, products of the genes.
11:14Now advances in biology were enabling scientists to base clocks directly on the genes themselves.
11:21This particular experiment was conducted by Charles Sibley and John Alquist at Yale University.
11:28tissue from an animal is ground down, in this case a chimpanzee, and the genetic material
11:32is extracted.
11:35This is the chimpanzee's DNA.
11:39Human DNA is obtained in the same way.
11:42DNA exists as two strands bonded in the form of a double helix.
11:48In the experiment, these strands are separated, and DNA from two species, here a chimp and
11:53a human, are allowed to link up.
11:56The more similar the genes of two species, the stronger this bond will be.
12:01To measure the strength of the bond, heat is used.
12:04Previously, this experiment was done with different species which had known divergence
12:09states.
12:11By comparing those measurements to the chimp-human measurement, Sibley and Alquist were able
12:15to calculate an approximate date for our divergence.
12:19We came up with about seven million years for the branch between the human line and
12:24the chimpanzee line, and about 10 million for the time that the gorilla line branched
12:29off.
12:31This work also showed that human genes are 97% the same as gorillas, and over 98% the
12:36same as chimps.
12:38The accumulation of evidence was changing the minds of many who had supported an earlier
12:42divergence state.
12:44I was wrong.
12:49As recently as five years ago, I thought that hominids had split from apes more than 10
12:56million years ago, maybe as much as 14 or 15 million years ago, and I don't think that
13:01anymore.
13:02I think that I was wrong.
13:03But what about a date as recent as 5 million years ago?
13:07It is more likely that hominids and African apes split 5 million years ago than that they
13:12split 15 million years ago, yes.
13:14I think that the minimum age is 5 million.
13:17It could be somewhat older.
13:20It could be, I mean, very conservatively, I would say 5 to 10.
13:23I very much doubt that it's as old as 10, but it's certainly not as old as 15.
13:29Even though many tests of the molecular clocks have indicated that evolutionary change proceeds
13:33at a constant rate, some critics still question its usefulness.
13:38Stephen Jones.
13:39It's a clock.
13:40There certainly is something in our molecules that's changing with time, and it's a clock
13:46in that sense.
13:47It's rather a peculiar clock.
13:48I don't know how useful it would be for us to regulate our lives with a clock that goes
13:53at different rates at different times, that goes at different rates in different species,
13:57and goes at dramatically different rates when we consider different molecules.
14:02Another point about the clock is that we don't know even when it started.
14:06It's rather noticeable, in fact, that people are constantly resetting their molecular clocks
14:11as new geological findings are made.
14:15So as I say, it's a useful clock, but it's a useful clock perhaps in the sense that Big
14:19Ben is useful.
14:20It's not much good as a stopwatch, which is what perhaps many human evolutionists are
14:24trying to use it for.
14:25I think it's got to be taken very seriously, although I don't think it's yet been demonstrated
14:29that it can be used as an exact clock to tell us an exact date.
14:33There are various factors which do cause changes in rates of evolution.
14:37But whatever the rate of change that we consider, there's no doubt that zoologically speaking,
14:42we are very, very close to the apes.
14:45So although the details of the molecular clock are still debated, these findings have been
14:49instrumental in changing people's ideas about the date of the ape-human divergence.
14:55It's changed 180 degrees.
15:00At that time, people, as I said, 20 million years was a conservative figure, and many
15:05people felt that the origin of the human line was even older.
15:09Now nobody, for all practical purposes, talks about more than 10 million years, and what
15:14people talk about is that there's a gap between 4 and 8 million.
15:17And so I think that that view has clearly shifted enormously, and I think that battle
15:22has been won.
15:24A battle has been won, but the exact time of the ape-human divergence is still in question.
15:30The fossil record is compared by scientists to the molecular clock to see if these different
15:35types of evidence point to similar conclusions about our origins.
15:44For most of the year, this barren Ethiopian valley is one of the hottest places on earth.
15:52When the torrential rains come in January, they wash away the dry dust and sand, exposing
15:57primeval geological features and sometimes traces of our past.
16:03It was here that in 1974, Donald Johansson discovered one of the most important and dramatic
16:09fossil finds of all time.
16:13This 3-foot-tall female skeleton lay in pieces and bits exposed by the rains and drifting
16:19earth.
16:20Almost 40% of it was recovered, a remarkable find for so ancient a being.
16:25She appeared to have walked erect, and at 3.5 million years was the oldest biped ever
16:29discovered.
16:31She was called Australopithecus afarensis, but nicknamed Lucy, and she was to become
16:36a star in human evolutionary history.
16:41Bipedality or upright walking is the crucial ability that separates humans from apes.
16:49No one is sure why early humans like Lucy might have opted for upright walking, but
16:53many evolutionary scientists think that this was the critical event in human evolution.
17:00It freed the hens to use tools and set the stage for the development of a larger brain.
17:07At Laetoli in Tanzania, a startling and unprecedented find gave further proof of these early bipeds.
17:14Mary Leakey and her team discovered the oldest footprints in the world, preserved here in
17:19a layer of volcanic ash.
17:21They were dated as just slightly older than Lucy, and although no fossil traces remain,
17:27these prints alone are evidence that 3.7 million years ago, our ancient ancestors walked here.
17:36This means that about two million years after Sarich's divergent state for humans and chimps,
17:41our forebears walked upright.
17:43Could the bipedalism apparent from Lucy's skeleton have developed so quickly?
17:53A chimpanzee has been anesthetized here at the State University of New York at Stony Brook.
18:00Researchers are now using new techniques to study chimps and humans to discover how and
18:04when upright walking evolved.
18:10Sensory electrodes are attached to some of the chimps' muscles.
18:14The researchers are Randall Sussman and Jack Stern.
18:20The procedure is not harmful, but the chimpanzee is kept anesthetized while the delicate electrodes
18:25and radio transmitters are taped on.
18:30They're studying the chimps' muscles to see what movements it shares with humans and other
18:34primates.
18:38The small radio transmitter on the chimps' back relays the signals from the electrodes.
18:44They're picking up the contraction of each muscle as the chimp moves along.
18:50A television camera documents what the animal is doing at any moment.
18:59By superimposing the two pictures, the researchers obtain an accurate record of which muscles
19:03are used during each phase of the walking cycle.
19:08This technique enables them to study bipedalism.
19:12Chimpanzees can use their muscles to walk upright, but they appear awkward and ungainly.
19:17Again, a record is made of the muscle contractions.
19:26A similar record is made of the muscle contractions as a human walks.
19:31This new type of information is now enhancing the more traditional ways of understanding
19:35how an ancient biped might have walked.
19:40A skeleton is also helpful in learning about the movements of an animal.
19:44One glance at a chimp's and an expert can tell that it is not bipedal.
19:50The skeleton of a human being reveals very clearly that we are.
19:55In humans, the thighs start wide apart and approach one another at the knees.
20:01In other words, we're knock-kneed.
20:03When the human walks, the knock-kneed position allows the feet to be placed in front of one
20:08another close to the same line.
20:11On the other hand, the chimpanzee is not knock-kneed.
20:14The thighs are parallel and run straight down to the knee.
20:18The effect of this is that when the chimpanzee walks bipedally on the ground, it walks with
20:24the feet spread apart.
20:28Whether Lucy walked like a chimpanzee or as we do is revealed in her skeleton.
20:33Lucy was like humans with knock-knees and unlike the chimpanzee with straight thighs.
20:43But there are more clues from her pelvis and from the muscle research in related primates.
20:49In the human pelvis, the blade curves around from back to front.
20:53We've been investigating the muscle that runs straight down from the blade to the top of
20:58the thigh.
20:59The effect of this muscle is that the human can walk upright on the straight thigh.
21:05The blade of the chimpanzee pelvis is different.
21:08The blade runs from inside out and those same muscles curves around down to the thigh rather
21:13than directly over the top and straight down.
21:17When the chimpanzee stands bipedally, in order to balance its trunk on its thigh, the chimpanzee
21:24must stand with a bent thigh.
21:31Lucy was knock-kneed and undoubtedly a biped.
21:35But this chimpanzee-like pelvis meant that her bipedality was not exactly like a human.
21:44With respect to the way Lucy walked, we think she may have walked like this.
21:52Lucy comes very early in the evolution of humans.
21:56She clearly shows signs of being able to walk on two legs better than any ape does, but
22:02not as well as you and I.
22:05She also shows signs of having spent far more time in the trees than any living human population,
22:12even those which climb for occasional gathering of fruits and nuts in the trees.
22:17Here's an animal whose locomotor behavior, whose movement behavior, was halfway between
22:22that of what we see in an ape today and what we see in our friends around us.
22:28Probably to progress from an ape to that halfway stage took two to three million years.
22:33And since Lucy herself is dated at three to four, that leaves a divergence point between
22:38six and seven million.
22:40In supporting a relatively recent divergence of the human ancestor from apes, our work
22:46ties in very closely to the molecular clock.
22:50So while Lucy does not prove a divergence date of five to seven million years, her existence
22:55as a bipedal ancestor of humans does fit well with Sarich and Wilson's findings.
23:01If bipedalism, in terms of the kind of evidence that we have currently from Lucy and her ilk,
23:08was shown 88 million years ago, then I would have to reevaluate the way in which we looked
23:14at the molecular data.
23:16It's entirely possible that we could be looking at it incorrectly.
23:19But the fact is that bipedalism has not been shown to occur earlier than about 3.7 million
23:24years ago.
23:25And that's well within the range that we projected.
23:29So if they find a 10 million year old biped, then we've got problems.
23:34But so far we don't have any problems.
23:36So far then, the molecular evidence is supported by fossil finds like Lucy.
23:41At 3.5 million years old, she lived well after the ape-human divergence date of five
23:46to seven million years indicated by the clocks.
23:50And the fossils offer other information about our origins.
23:53Lucy appears to have paved the way for the new genus Homo, whose first member, Homo habilis,
23:59lived 1.9 million years ago and was the first toolmaker.
24:04A few hundred thousand years after Habilis, Homo erectus appeared, a great leap forward
24:09from earlier peoples.
24:13Homo erectus learned how to control fire and used more sophisticated stone tools.
24:19They also must have been prodigious travelers, for the fossil record indicates that groups
24:23of Homo erectus left their ancestral home and migrated around the world.
24:28One million years ago, according to an accepted theory, they traveled north out of Africa
24:33and spread into Europe, Asia, and down towards Australia.
24:38On the island of Java in Indonesia, several Homo erectus skulls have been found.
24:43In China, other skulls dating from the same era have also been discovered.
24:48These and other fossils are proof of Homo erectus' movements.
24:52Homo erectus appears to have evolved over hundreds of thousands of years to more modern
24:57people, sometimes called Neanderthals.
25:01Little was known about these people until the last century, when a discovery was made
25:05in Germany at the Neander Valley.
25:08Here a skeleton was found in a cave.
25:10At first it was thought to be the remains of a refugee from Noah's flood, or a hermit,
25:15or a deserter from the Cossack army.
25:18Another skull had been found a few years earlier in Gibraltar, but no one had realized its
25:23true significance.
25:25By the turn of the century, their existence was well documented.
25:29Early analysis of fossil finds led scientists to infer that Neanderthals must have been
25:34people of limited intelligence who lived a brutal existence.
25:38However, new fossil finds challenged the assumptions about these early humans.
25:45This film was shot in northern Iraq in the 1950s by Ralph Saleki, a young anthropologist.
25:51Local Kurdish tribespeople guided him to a cave called Shanidar.
25:56With their help, he began digging down into the floor.
26:01This excavation would lead to one of the most remarkable of all the finds of these
26:05early people.
26:09After several feet of painstaking work, they discovered a grave many thousands of years
26:13old.
26:15In it were the bones of a Neanderthal man.
26:19Around the bones, the soil contained large amounts of pollen.
26:22It was pollen from the local flowers, and it has been assumed that these had been buried
26:27along with his body, a gesture that transcends time and belies the image of Neanderthals
26:32as brutal, primitive people.
26:36Many other Neanderthal graves have been found throughout Europe and Western Asia.
26:42From this data, it is assumed that they buried their dead, something earlier peoples appear
26:47not to have done.
26:49Other important information from this find is that the Shanidar male, who was about 40
26:53years of age, old for those days, had been for years a walking textbook of ailments.
26:59Eric Trinkaus.
27:01This is an individual who had a whole series of injuries.
27:04He had, he sustained a blow to the outside of one of his eye sockets that fractured the
27:10bone and healed over.
27:11It was along on, it would have been along this side of the individual.
27:15He was almost certainly blind in that eye.
27:18That same individual had a withered right arm.
27:21His, what remains of the arm is about half the size of the one on the other side.
27:26It's again a childhood injury that would have made that arm essentially useless.
27:32The same individual also had a fracture of one of the bones of his feet, he had arthritis
27:37in his knee and his ankle.
27:38It was an individual who was in very bad shape, and he was in very bad shape, would have had
27:44trouble walking, seeing, using one of his arms.
27:48The implication is that he had been taken care of for many years, despite the fact that
27:53he was probably not very economically useful to a group of hunter-gatherers.
27:56Why?
27:57The main reasons for keeping somebody alive are either something emotional, a feeling
28:05of some kind of affinity towards that individual, the same way we try to keep our elderly relatives
28:10alive.
28:12The only other reason is that as long as you can keep that person alive, that individual
28:18can nonetheless be a source of information.
28:22For people so much at the mercy of their environment, important information might have been about
28:26the world around them.
28:28For instance, how had the group survived the winters of ten or twenty years before?
28:32Yet, other evidence indicates that their communication might have been limited after
28:42all.
28:44The clues come from careful studies of the fossils themselves.
28:50Ancient bones from Neanderthal skeletons and new computer technology are enabling scientists
28:54to create a more accurate vision of early humans.
29:00Other techniques are used by medical researchers to test artificial joints.
29:05A bone is embedded in plastic and then cut into sections.
29:10A photograph of the bone's cross-section is projected onto a screen, while a member of
29:14the research team uses an electronic pen to trace its outline.
29:19This drawing is used to model mathematically what will happen to this bone as it undergoes
29:23different stresses and supports various amounts of weight.
29:28These methods have allowed scientists to produce a detailed description of the body
29:31and build of the Neanderthals.
29:34Your average Neanderthal, whether it's a man, woman, or child, would be at least as strong
29:39and probably considerably stronger than your average highly trained modern human weightlifter.
29:46You get a tremendous buildup of bone in the shaft of a long bone as a result of resistance
29:51to fatigue.
29:53And the tremendous amount of bone we see in the Neanderthal leg bones in particular is
29:57an indication that they had much more endurance than we do, and a tremendous amount of endurance.
30:03And the only way that we can explain that is if they were spending a lot of their waking
30:09hours moving around the landscape in search of food, walking in a not very directed way.
30:16And what that implies to us is that they were not very highly organized about this.
30:21One of the things you see in modern human hunters and gatherers is they have a very
30:24intimate knowledge of the environment around them, and that they spend a lot of time sharing
30:28that information and communicating it amongst themselves within a social group and with
30:33other groups.
30:34The implication for the Neanderthals is that they did relatively little of that kind of
30:39information sharing, that they went out on a very opportunistic way simply looking for
30:44whatever they happened to run across.
30:47From this analysis, scientists have created an image of a rather inefficient people.
30:53Nevertheless, they endured for hundreds of thousands of years until the advent of more
30:57modern beings.
30:59Thirty-five thousand years ago, the Neanderthals were joined by Cro-Magnons.
31:04These people were modern Homo sapiens, the immediate ancestors of contemporary humans.
31:11The story that their fossils tell is of a people who seemed in many ways much like the
31:15people of today.
31:18The main differences we see between Neanderthals and their immediate successors, early modern
31:22humans, was that those early modern humans were far less massively built.
31:26For example, if you compare this upper arm bone of a Neanderthal to this one of an early
31:30modern human, you can see very clearly that the shafts of them are markedly different
31:35in diameter.
31:36This is just one indication of a major reduction in muscularity and endurance and everything
31:45that goes along with that.
31:47Why might the physically weaker Cro-Magnons have survived while the more robust Neanderthals
31:52did not?
31:54The Cro-Magnons were different.
31:56They were built like us.
31:58They obviously must have had a way of getting food which did not require such robusticity
32:03and muscularity.
32:04They must have been more efficient at finding their food.
32:06They were probably able to plan ahead for a long period of time.
32:09They knew where the local resources were.
32:12They knew where the game was.
32:13They knew where the water was.
32:14They knew where the raw materials, such as flint, were.
32:16And they were able to get to them quickly with much less effort than the Neanderthals
32:20could do.
32:22There is striking evidence of their communication skills in their art.
32:26They covered the walls of their caves with paintings of their daily life, their hopes
32:30and their plans, something the Neanderthals never did.
32:35For a long time, scientists believed that the Neanderthals evolved into these Cro-Magnon
32:39people and that we are therefore descended from the Neanderthals.
32:43But some disagree.
32:45I don't think the Neanderthals evolved into modern people and modern Europeans.
32:48And I think the easiest way to demonstrate it is to look at a couple of specimens and
32:52see the differences between them.
32:54The Cro-Magnon skull is really essentially modern.
32:56I mean, there are very few differences from our own skeletons.
33:00And the main features to note are the small brow ridge, very small indeed by the standards
33:05of earlier people, a small face tucked in under the brain box, quite a small nose, small
33:11teeth and overall a rounded and rather short skull.
33:16And compared with that, we've got the Neanderthals with this massive brow ridge over the orbits,
33:21a very large nose and a face which is pulled forward, large front teeth and a skull shape
33:26that overall is long and low and very different from our own.
33:29But I think personally there's no possibility that the Neanderthal could have evolved into
33:34the Cro-Magnon because the differences between them are too great and there was no time in
33:38Europe to turn a late Neanderthal into an early Cro-Magnon.
33:41And evolution isn't capable of changing to such different things from one to the other
33:46in such a short period of time.
33:47So the Neanderthals, in my view, are not our ancestors.
33:50They were descendants of Homo erectus in Europe that had their own evolution which went on
33:54for probably 300,000 years and then came to a dead end about 30 to 35,000 years ago.
34:00And the Neanderthals, instead of being our ancestors, were replaced by modern looking
34:05people who came in from somewhere else.
34:07Springer favors another theory.
34:09He accepts the idea that an original migration of Homo erectus occurred a million years ago
34:15leading to different populations all over the world.
34:19But he believes there was another migration very recently.
34:23Once again, this started in Africa.
34:26These people populated that continent and then gradually moved north, spreading to all
34:31the continents and inhabiting the world between 50 and 30,000 years ago.
34:38This would explain why humans are uniquely similar genetically compared to other species.
34:43Our apparent differences, such as skin color, are very superficial and involve very few
34:48genes.
34:49What I'd like you to do is to put on your goggles before you go into the box.
34:55Can you please step this way?
34:58Here volunteers are exposed to high doses of ultraviolet radiation to determine how
35:03their skin reacts to light.
35:06This experiment is helping researchers to understand how differences in skin pigmentation
35:10might have evolved.
35:13Skin colors seem to have different advantages in different environments.
35:16For instance, a darker pigment protects against the harsh equatorial sun.
35:21And a lighter skin in a less sunny climate aids in the making of vitamin D.
35:25Michael, how was that?
35:26No problem.
35:27Okay, great.
35:31It's believed that early man was probably heavily pigmented.
35:34And more than likely, because he was living at the equator, that he was capable of making
35:37more than enough vitamin D.
35:39However, as he migrated north of the equator and settled in, more than likely he would
35:44have had to lose his pigmentation or become paler in order to make adequate vitamin D
35:48because the sun's rays are much weaker in northern climates.
35:51And because he's probably a hunter and gatherer of food, that to have weak bones because of
35:56vitamin D deficiency would have caused a very serious problem.
35:59And as a result, probably skin pigmentation had to disappear.
36:02This research supports the theory that Cro-Magnons descended from people who moved north, migrating
36:07out of Africa.
36:09The fossil record also indicates that Cro-Magnons and Neanderthals lived for a short time in
36:13the same regions.
36:15Did they interbreed?
36:16Well, I personally doubt that there was very much.
36:18There could well have been some because genetically, I don't think we can doubt that Neanderthals,
36:22even if they weren't our ancestors, were very closely related to us.
36:26But I think that the interbreeding would have been on a very, very low scale, although it
36:29is claimed that there are fossils from Europe which are hybrids between Neanderthal and
36:33modern people.
36:34But I think that hasn't been demonstrated yet.
36:36We have to keep an open mind.
36:38Many of these questions about early peoples cannot be answered from the fossil record
36:42alone.
36:43We have seen how biological investigations in other species can be used to understand
36:49relatedness between apes and humans.
36:56But Neanderthals and Cro-Magnons no longer exist.
36:59So to answer many of the questions about their roles in evolution, we must turn to the only
37:03living evidence that is available, our own species.
37:07DNA fingerprinting is a recent and powerful technique that allows scientists to look into
37:13the genes themselves and to extract information about our human heritage.
37:18These horizontal rows indicate specific DNA segments from six different individuals.
37:23Two are identical twins.
37:25They have the same dark bands level with each other.
37:28Their mother is at the top line with three possible fathers at the bottom.
37:32First, researchers look for which half of the genes were given by the mother.
37:37At least two groups are immediately obvious.
37:41Then the fathers are checked to see which gave the rest.
37:44Again, two groups can be immediately identified.
37:49Father number one must be the parent.
37:51The odds are many millions to one against it being wrong.
37:55This technique is very useful for comparing two generations.
37:59Similar techniques can be used when comparing individuals separated by dozens of generations.
38:05A cell nucleus is broken open and the DNA released.
38:09This is exposed to restriction enzymes, which act like chemical knives, cutting the strands
38:14of DNA into pieces.
38:16But occasionally an enzyme cannot cut the DNA.
38:20This is because a mutation has changed the structure at that point.
38:26The next step is that each individual sample of sliced up DNA is injected into a different
38:30position in a gel marked by this purple dye.
38:36We all carry mutations which we've inherited from our parents and they from their parents
38:40before them.
38:42In many cases we will have mutations in common with other far distant relatives in the same
38:46population.
38:52It is the patterns of these mutations that are the crucial markers which enable scientists
38:56to trace our heritage over thousands of years.
39:02To make the patterns obvious, an electric current is applied across the samples.
39:12The electric charges are transmitted through this medium, causing the bits of sliced up
39:17DNA in the gel to move.
39:19The short pieces move fastest.
39:21The longest pieces, those that would not cut, hang back.
39:30After several hours, the chopped up DNA with its information about our past has spread
39:35down the gel and can be seen under ultraviolet light.
39:40A photograph called an autoradiograph is later made to preserve this image.
39:46By studying the patterns in these dark bands of DNA, it's possible to discover who shares
39:51mutations and when they might have had a common ancestor.
40:02Attempts have already been made to find remnants of DNA preserved in the bodies of Egyptian
40:07mummies.
40:13Such studies are interesting because, theoretically, they can reveal the relatedness between modern
40:18Egyptians and their ancestors, the pharaohs.
40:23Let's imagine we had the globin sequence from a mummy and from a modern Egyptian.
40:27By comparing the two, we could tell us, we could learn what the patterns of relatedness
40:31between them were.
40:32Are modern Egyptians indeed related, descended from their famous pharaonic ancestors or are
40:39they not?
40:40There are some more local questions you can ask.
40:43Is it indeed the case that there was extensive incest among the pharaohs, as is often claimed?
40:47We should certainly be able to tell that if we can sequence their DNA.
40:53For people living today, it is possible to trace where their ancestors came from thousands
40:57of years ago by looking for specific mutations in their genes.
41:04How Polynesians got to their isolated Pacific islands is a compelling mystery.
41:12Back in the 40s, the explorer Thor Heyerdahl maintained that they could have crossed from
41:16South America on balsa wood rafts.
41:19He successfully sailed such a raft across the Pacific, ending up here, grounded on the
41:23rocks.
41:25An Oxford group has used DNA studies to investigate his theory.
41:30Adrian Hill.
41:31In 1947, Thor Heyerdahl sailed his balsa raft, the Kontiki, from here, off the coast of Peru,
41:404,000 miles across the Pacific to central Polynesia in an attempt to show that the Polynesians
41:45could have come from South America.
41:47However, the linguists and archaeologists disagreed, maintaining that instead they had
41:52originated in Southeast Asia.
41:55Recently, we've been able to identify some mutations in DNA, which are found in Polynesians,
42:02Melanesians, and island Southeast Asians, but not anywhere else in the world.
42:07It looks now as if these are very useful genetic markers for plotting a migration route by
42:12the Polynesians, starting here in Southeast Asia, moving through island Melanesia some
42:183,000 to 4,000 years ago, and from there, spreading out into the Pacific.
42:23So now the archaeological, linguistic, and genetic data are all in agreement that the
42:28colonization of Polynesia was predominantly from the West.
42:32And although Heyerdahl's was a brave attempt, he was wrong.
42:38By further study of the DNA of Polynesians and people of other races, researchers are
42:43attempting to discover where they and everyone else in the world originated.
42:48Another member of the Oxford group, James Wainscott.
42:51A recent migration took place, a relatively small number of human beings out of Africa.
42:57These human beings migrated through Europe, through Asia, down to Australia, and also
43:02into the Americas.
43:03In other words, this original small migration of people out of Africa have subsequently
43:09given rise to all the world's present-day populations.
43:13These DNA studies lend support to the theory, based on fossils, that after the Homo erectus
43:18migration about one million years ago, there was another, much more recent migration out
43:23of Africa of modern people who populated the globe.
43:29Almost all of the studies of genes and fossils agree that Africa is an ancestral home to
43:33all present-day people.
43:36But new DNA investigations are now challenging many widely accepted theories about our origins.
43:44Here at Emory University in Georgia, scientists are working with recently discovered genetic
43:48clues.
43:49They are arriving at some startling and unexpected findings about our human prehistory.
43:56Most of the genetic research into human evolution has concentrated on the DNA found here in
44:02the cell's nucleus.
44:06But mitochondria, these small organelles in the cell's cytoplasm, have recently gained
44:10new importance for evolutionary biologists.
44:13For housed here is another kind of DNA that obeys very unusual laws of inheritance.
44:19In the early 1970s, my collaborators and I started looking at the mitochondrial DNA of
44:24humans to try and understand the rules of its inheritance.
44:28During that same period, other workers working in other animal systems made an important
44:33observation, and that is that the mitochondrial DNAs of toads and other kinds of animals was
44:39inherited exclusively from the mother.
44:41See all the kids are here.
44:42I thank you very much for coming by and volunteering to participate in our DNA study.
44:49To see if the mitochondrial DNA pattern of inheritance would be the same in humans, Wallace
44:54and his team located families that could be traced through two, three, and four generations
45:00and asked each member to donate blood.
45:04The samples were then spun in a centrifuge to separate out the portion of the blood that
45:08contains the greatest concentration of mitochondrial DNA.
45:14The mitochondrial DNA was isolated and then sliced into segments just as we've seen with
45:19nuclear DNA.
45:23The same techniques are used to reveal the patterns in the genes, which are again photographed
45:28to produce an autoradiograph.
45:32This is an autoradiograph that shows the mitochondrial DNAs of a father, mother, and their two children.
45:40You can see for this particular band that the mother and the father differ markedly.
45:45The mother has this fragment, the father lacks it.
45:48When we look at the mitochondrial DNA of the two children, we can see that they clearly
45:53have this band that the mother has but that the father lacks.
45:58This kind of analysis shows us unequivocally that the mitochondrial DNA was inherited exclusively
46:03from the mother and not from the father.
46:07This maternal pattern of inheritance is of great significance for evolutionary biology.
46:12The more familiar DNA, nuclear DNA, is inherited from both our mother and our father.
46:18What this means is that each parent randomly contributes half of these genes to their children.
46:23Each new generation then accumulates more variations in its genes.
46:28These patterns become dispersed throughout the population in a crazy jigsaw of combinations
46:33that makes it difficult to track paths of inheritance.
46:36But this maternally transmitted DNA is different.
46:39The mitochondrial DNA is exciting for historical studies because it represents a unique kind
46:46of biological history book.
46:48This history book is a much clearer picture of recent human history than is available
46:53through genes that are located in the nucleus.
46:55And this has given us new insight into human origins and recent prehistory that has not
47:01been possible through nuclear gene studies.
47:05Wallace and his team reasoned that the way to discover the ancestral home of modern people
47:10was to locate the population that had the most ancient mitochondrial DNA.
47:15They collected blood samples from different racial populations around the world and began
47:19studying the patterns of variations between groups.
47:24They analyzed the data in a number of ways.
47:26Since they knew that humans had originally shared a common ancestor with the apes, they
47:31also compared human mitochondrial DNA to that of other primates.
47:37They decided to look for the contemporary human population which had patterns of mitochondrial
47:41DNA that were most similar to those commonly found in primates.
47:46This they thought would be the human population with the oldest link to the original source
47:51of the mitochondrial DNA.
47:53We compared the mitochondrial DNA variants of the human forms with those of other primates.
47:58When we did that, we found that a mitochondrial DNA that's found primarily in Asia was the
48:03most similar to that found in the other primates.
48:06So this raised the possibility that in fact the real root of the mitochondrial DNA tree
48:10was in Asia, not Africa.
48:13According to this interpretation, Asia, not Africa, was the true home of modern people.
48:19This is a startling and unexpected conclusion that if true, confounds most theories of human
48:24migration as well as the fossil record.
48:29We're not concerned particularly at this point that the fossil evidence suggests an African
48:34origin because in our opinion, our best thing that we can do is study the genetic history.
48:41Even though our work is still very early in its infancy, we believe that there is a lot
48:46of information there and that we will gain a lot of insight as the years go by.
48:51In this new research, the interpretation of the data depends on the methods of analysis.
48:57Wallace and his team can analyze their data in other ways that do point to Africa as our
49:01land of origin.
49:03This agrees with the conclusions of another team at the forefront of the field.
49:08So let's start with your mother.
49:10Was she born in the U.S.?
49:12Yes, she was born in New York.
49:14About what time?
49:15Rebecca Kan at the University of California at Berkeley also sampled mitochondrial DNA
49:21for her studies of human origins.
49:23She asked women about their family history to learn about their recent female ancestry.
49:28We thought when we started out we would be able to trace the movement of women throughout
49:33the world.
49:34We wanted to be able to look at the way people migrated and because there were differences
49:40between the way males move and the way females move and historically women were often treated
49:45as property and so they were traded along with livestock or with flints or things like
49:51that and so there were ways we thought of testing hypotheses that people had about where
49:58we all came from and correlating genetics with oral history and with written histories
50:05in certain populations.
50:06We thought we would get an idea of where the human species came from, modern people, anatomically
50:12modern people, and perhaps when our own species arose.
50:17When's the baby due?
50:18In four months.
50:19Four months, so that's February?
50:24End of March.
50:25End of March.
50:26Okay.
50:27Thanks for agreeing to come in and talk and thanks for agreeing to donate your placenta.
50:34Kan used placentas donated by new mothers as her source of mitochondrial DNA.
50:39Like the researchers in Georgia, she and her team collected samples from diverse racial
50:44populations, but they relied on a different method of analysis from that which had led
50:48Douglas Wallace to his unexpected finding.
50:52You look for the population that has the greatest number of differences.
50:56If you're comparing DNA sequences, you want to see the greatest number of mutations that
51:01are shared within that particular group.
51:07In their samples, the Kung people of the Kalahari from Africa were the population that contained
51:11the greatest amount of variation in their mitochondrial DNA.
51:18The Berkeley group reasoned, therefore, that human beings must have been in Africa longer
51:22than anywhere else.
51:25But there is a more remarkable finding that both the Georgia and California teams agree
51:29on.
51:31When they compared the mitochondrial DNA patterns in people alive today, they realized that
51:36the patterns linked up into branches.
51:39These could be traced backwards to early discrete populations with similar specific mutations.
51:45But their most provocative suggestion was that about 200,000 years ago, these branches
51:50linked up into one single source for all the mitochondrial DNA that exists today.
51:55Our major conclusion was that the human species, the group that gave rise to us, whether we
52:01call them anatomically modern humans, homo sapiens, sapiens, or whatever, that population
52:07contained a woman, an Eve if you want to call her that, and she was somewhere in Africa.
52:14She belonged to a group which spread throughout all areas of the world, and we're all descended
52:19from her.
52:21This is a powerful notion.
52:23Every single human being who is alive today carries within a vestige of this great, great
52:28grandmother of modern people.
52:30For thousands of generations, her genetic legacy has traveled from woman to woman.
52:36But even though all our mitochondrial DNA may be descended from this common ancestor,
52:41she would not have been the sole founder of the human race.
52:45We don't feel that this data proves or shows that there was only one woman as a founder.
52:52There are certain aspects of the mitochondrial DNA inheritance that could well result in
52:57many founding women's mitochondrial DNAs being lost, and this can be easily understood
53:03by just thinking about the inheritance.
53:05Let's take for an example two women, one of which has two daughters and the other of which
53:10has two sons.
53:12It's clear that the mitochondrial DNA of the woman that had two sons is now lost to all
53:16of history.
53:18So we are unable from just looking at the lineage of today's mitochondrial DNAs to deduce
53:22exactly how many founding women there were.
53:26Depending on parameters such as population size and other factors, this number could
53:30be a small number up to a number in the thousands.
53:34This is not exactly a modern Adam and Eve story about our origins.
53:39Although only one woman gave us our mitochondrial DNA, many of the other women of her time contributed
53:44the nuclear DNA that exists today.
53:49Yet only she would have spawned all the mitochondrial DNA that each of us carries.
53:54If this is true, it has powerful implications for our understanding of human history.
54:00I think one of the things that I found most personally exciting about our discovery of
54:05a single female lineage of mitochondrial DNA is it showed how closely related all of the
54:11different people on our globe are to each other, and that in fact we really are part
54:16of one human family, all of which tracing back to a few human ancestors.
54:25Sometimes as science struggles to address the fundamental issues of our evolution, more
54:29questions are raised than answered.
54:32The theories of our distant past based on contemporary genetic samples are still very
54:36controversial.
54:38But the study of our origins has always been one of radical ideas and startling upheavals.
54:45Human history is constantly rewritten as evidence grows and interpretations change.
54:53We may never learn every chapter of our evolution, but we now know that in addition to all we
54:59can discover from the fossils, each and every one of us carries in our genes messages from
55:04our past, messages that may someday reveal the roads that we as a species have traveled.
55:45♪♪♪
55:55♪♪♪
56:15For a transcript of this program, send $4 to NOVA, Box 322, Boston, Massachusetts, 02134.
56:33Please be sure to include the show title.
56:36To purchase film or video copies of this program for educational use, call toll-free 1-800-621-2131.
56:44In Illinois or Alaska, call COLLECT, 312-940-1260.
56:54Major funding for NOVA is provided by this station and other public television stations
56:59nationwide.
57:01And by Allied Signal, a technology leader in aerospace, electronics, automotive products,
57:07and engineered materials.
57:13The Johnson & Johnson family of companies, supplying healthcare products worldwide.