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00:00:00Satsang with Mooji
00:00:30Mooji
00:01:00All my life I've wondered about life beyond the Earth.
00:01:07On those countless other planets that we think circle other suns, is there also life?
00:01:14Might the beings of other worlds resemble us, or would they be astonishingly different?
00:01:19What would they be made of?
00:01:21In the vast Milky Way galaxy, how common is what we call life?
00:01:27The nature of life on Earth and the quest for life elsewhere are the two sides of the same question.
00:01:37The search for who we are.
00:01:39All living things on Earth are made of organic molecules, a complex microscopic architecture built around atoms of carbon.
00:01:54In the great dark between the stars, there also are organic molecules in immense clouds of gas and dust.
00:02:02And inside such clouds, there are batches of new worlds just forming.
00:02:12Their surfaces are very likely covered with organic molecules.
00:02:16These molecules almost certainly are not made by life, although they are the stuff of life.
00:02:21Unsuitable worlds, they may lead to life.
00:02:25Organic matter is abundant throughout the cosmos, produced by the same chemistry everywhere.
00:02:32Perhaps given enough time, the origin and evolution of life is inevitable on every clement world.
00:02:55There will surely be some planets too hostile for life.
00:02:59On others, it may arise and die out, or never evolve beyond its simplest forms.
00:03:05And on some small fraction of worlds, there may develop intelligences and civilizations more advanced than ours.
00:03:16All life on our planet is closely related.
00:03:20We have a common organic chemistry and a common evolutionary heritage.
00:03:24And so our biologists are profoundly limited.
00:03:29They study a single biology.
00:03:31One lonely theme in the music of life.
00:03:36Is it the only voice for thousands of light years?
00:03:39Or is there a cosmic fugue?
00:03:42A billion different voices playing the life music of the galaxy.
00:03:47This blue world is where we grew up.
00:03:56There was once a time before life.
00:03:58Our planet is now burgeoning with life.
00:04:01How did it come about?
00:04:03How were organic molecules originally made?
00:04:06How did life evolve to produce beings as elaborate and complex as we?
00:04:13Able to explore the mystery of our own origins.
00:04:20Let me tell you a story about one little phrase in the music of life on Earth.
00:04:25In the history of humans, in the 12th century, Japan was ruled by a clan of warriors called the Heike.
00:04:55The nominal leader of the Heike, the emperor of Japan, was a seven-year-old boy named Antoku.
00:05:09His guardian was his grandmother, the lady Ni'i.
00:05:12The Heike were engaged in a long and bloody war with another samurai clan, the Genji.
00:05:34Each asserted a superior ancestral claim to the imperial throne.
00:05:39Their decisive encounter occurred at Tanu-ura, in the Japanese inland sea, on April 24th, in the year 1185.
00:05:55The Heike were badly outnumbered and outmaneuvered.
00:05:59With their cause clearly lost, the surviving Heike warriors threw themselves into the sea and drowned.
00:06:06The emperor's grandmother, the lady Ni'i, resolved that they would not be captured by the enemy.
00:06:18What happened next is related in the tale of the Heike.
00:06:23The young emperor asked the lady Ni'i,
00:06:25Where are you to take me?
00:06:28She turned to the youthful sovereign, with tears streaming down her cheeks, and comforted him.
00:06:46Blinded with tears, the child sovereign put his beautiful small hands together.
00:06:52He turned first to the east, to say farewell to the god of Issei.
00:07:00And then to the west, to recite the Nembutsu, a prayer to the Amida Buddha.
00:07:07The lady Ni'i took him in her arms, and with the words,
00:07:11In the depths of the ocean is our capital, sank with him at last beneath the waves.
00:07:17The destruction of the Heike battle fleets at Dano Ura marked the end of the clan's 30-year rule.
00:07:46Now, the Heike all but vanished from history.
00:07:54Only 43 Heike survived, all women.
00:07:58These former ladies-in-waiting of the imperial court were reduced to selling flowers and other favors
00:08:05to the fishermen near the scene of the battle.
00:08:08These women, and their offspring by the fisher-folk, established a festival to commemorate the battle.
00:08:21To this day, every year, on the 24th of April, their descendants proceed to the Akama Shrine,
00:08:35which contains the mausoleum of the drowned seven-year-old emperor, Antoku.
00:08:41There, they conduct a ceremony of remembrance for the life and death of the Heike warriors.
00:08:52But there's a strange postscript to this story.
00:09:03The fishermen say that the Heike samurai wander the bottom of the inland sea still,
00:09:10in the form of crabs.
00:09:12There are crabs to be found here, which have curious markings on their backs.
00:09:18Patterns which resemble a human face, with the aggressive scowl of a samurai warrior from medieval Japan.
00:09:26These Heike crabs, when caught, are not eaten.
00:09:38They're thrown back into the sea, in commemoration of the doleful events of the Battle of Dano Ura.
00:09:56This legend raises a lovely problem.
00:10:01How does it come about that the face of a warrior is cut on the carapace of a Japanese crab?
00:10:08How could it be?
00:10:10The answer seems to be that humans made this face.
00:10:15But how?
00:10:16Like many other features, the patterns on the back or carapace of this crab are inherited.
00:10:23But among crabs, as among humans, there are many different hereditary lines.
00:10:28Now, suppose purely by chance, among the distant ancestors of this crab,
00:10:35they came to be one which looked just a little bit like a human face.
00:10:40Long before the battle, fishermen may have been reluctant to eat a crab with a human face.
00:10:46In throwing it back into the sea, they were setting into motion a process of selection.
00:10:52If you're a crab and your carapace is just ordinary, the humans are going to eat you.
00:10:59But if it looks a little bit like a face, they'll throw you back and you'll be able to have lots of nice little baby crabs that all look just like you.
00:11:07As many generations past, of crabs and fisher folk alike.
00:11:14The crabs with patterns that look most like a samurai face preferentially survived.
00:11:20Until eventually, there was produced not just a human face, not just a Japanese face, but the face of a samurai warrior.
00:11:29All this has nothing to do with what the crabs might want.
00:11:34Selection is imposed from the outside.
00:11:37The more you look like a samurai, the better your chances of survival.
00:11:41Eventually, there are a lot of crabs that look like samurai warriors.
00:12:08This process is called artificial selection.
00:12:12In the case of the Heikki crab, it was affected more or less unconsciously by the fishermen,
00:12:17and certainly without any serious contemplation by the crabs.
00:12:22Humans, for thousands of years, have deliberately selected which plants and animals shall live.
00:12:29We're surrounded with farm and domestic animals, fruits, vegetables.
00:12:35Where did they come from?
00:12:37Were they once free living in their present form in the wild and then induced to adopt some less strenuous life on the farm?
00:12:43No.
00:12:45They are, almost all of them, made by us.
00:12:49The essence of artificial selection for a horse or a cow, a grain of rice or a Heikki crab, is this.
00:13:01Many characteristics are inherited. They breed true.
00:13:06Humans encourage the reproduction of some varieties and discourage the reproduction of others.
00:13:12The variety selected for eventually becomes abundant.
00:13:16The variety selected against becomes rare, maybe extinct.
00:13:20But if artificial selection makes such changes in only a few thousand years,
00:13:26what must natural selection, working for billions of years, be capable of?
00:13:33The answer is all the beauty and diversity in the biological world.
00:13:43That life evolved over the ages is clear from the changes we've made in the beasts and vegetables,
00:13:51but also from the record in the rocks.
00:13:55The fossil evidence speaks to us unambiguously of creatures that were once present in enormous numbers
00:14:03and that have now vanished utterly.
00:14:05There are far more species that have become extinct than exist today.
00:14:09They're the terminated experiments in evolution.
00:14:14These guys, for example, the trilobites, appeared 600 million years ago.
00:14:19They were around for 300 million years. They're all gone.
00:14:23There's none left.
00:14:25But in those old rocks, there are no fossils of people or cattle.
00:14:30We've evolved only recently.
00:14:32Evolution is a fact, not a theory. It really happened.
00:14:44That the mechanism of evolution is natural selection
00:14:47was the great discovery of Charles Darwin and Alfred Russell Wallace.
00:14:52Here's how it works. Nature is prolific.
00:14:56There are many more creatures that are born than can possibly survive.
00:15:00So those varieties, which are by accident less well-adapted, don't survive.
00:15:07Or at least they leave fewer offspring.
00:15:09Now, mutations, sudden changes in heredity, are passed on.
00:15:15They breed true.
00:15:16The environment selects those occasional mutations which enhance survival.
00:15:21And the resulting series of slow changes in the nature of living beings
00:15:26is the origin of new species.
00:15:28Well, many people were scandalized by the ideas of evolution and natural selection.
00:15:35Our ancestors looked at the intricacy and beauty of life
00:15:40and saw evidence for a great designer.
00:15:44The simplest organism is a far more complex machine than the finest pocket watch.
00:15:54And yet, pocket watches don't spontaneously self-assemble
00:15:58or evolve in slow stages on their own from, say, grandfather clocks.
00:16:04A watch implies a watchmaker.
00:16:08So, there seemed to be no way in which atoms could spontaneously fall together
00:16:14and create, say, a dandelion.
00:16:20The idea of a designer is an appealing and altogether human explanation of the biological world.
00:16:27But, as Darwin and Wallace showed, there's another way.
00:16:33Equally human, far more complex.
00:16:37Natural selection, which makes the music of life more beautiful as the eons pass.
00:16:50To understand the passage of the eons, we've compressed all of time into a single cosmic year
00:16:55with the Big Bang on January 1st.
00:16:59Every month here represents a little over a billion years.
00:17:04The Earth didn't form until the cosmic year was two-thirds over.
00:17:08Our understanding of the history of life is very recent,
00:17:12occupying only the last few seconds of December 31st,
00:17:16that small white spot at bottom right in the cosmic calendar.
00:17:19What happened on Earth may be more or less typical of the evolution of life on many worlds.
00:17:25But, in its details, the story of life on Earth is probably unique in all the Milky Way galaxy.
00:17:33The secrets of evolution are time and death.
00:17:38Time for the slow accumulation of favorable mutations,
00:17:42and death to make room for new species.
00:17:45Life on Earth arose in September of the cosmic calendar,
00:17:50when our world, still heavily battered and cratered from its violent origin,
00:17:55may have looked a little like the moon.
00:17:59The Earth is about four and a half billion years old.
00:18:03In the cosmic calendar, it condensed out of interstellar gas and dust around September 14th.
00:18:10We know from the fossil record that the origin of life happened soon afterwards,
00:18:15maybe around September 25th, something like that,
00:18:19probably in the ponds and oceans of the primitive Earth.
00:18:23Now, the first living things were not anything so complex as a one-celled organism,
00:18:28which already is a highly sophisticated form of life.
00:18:32No, the first stirrings of life were much more humble,
00:18:35and happened on the molecular level.
00:18:39In those early days, lightning and ultraviolet light from the sun
00:18:43were breaking apart simple hydrogen-rich molecules in the primitive atmosphere,
00:18:48and the fragments of the molecules were spontaneously recombining
00:18:52into more and more complex molecules.
00:18:55The products of this early chemistry dissolved in the oceans,
00:19:03forming a kind of organic soup of gradually increasing complexity.
00:19:08Until, one day, quite by accident,
00:19:12a molecule arose which was able to make crude copies of itself,
00:19:17using as building blocks the other molecules in the soup.
00:19:19This was the ancestor of DNA, the master molecule of life on Earth.
00:19:27It's made of four different molecular parts called nucleotides,
00:19:31which constitute the four letters of the genetic code, the language of heredity.
00:19:37Each of the four nucleotides, the rungs on the DNA ladder,
00:19:42are a different color in this model.
00:19:44The instructions that are spelled out are different for different organisms.
00:19:49That's why organisms are different.
00:19:51Now, a mutation is a change of a nucleotide,
00:19:55a misspelling of the genetic instructions.
00:19:58Most mutations spell genetic nonsense, as you'd expect,
00:20:02because they're random.
00:20:04They're harmful for the next generation.
00:20:06But a very few, by accident, make better sense than the original instructions
00:20:11and aid the evolution of life.
00:20:12DNA is about a billion times smaller than we see it here.
00:20:19In fact, each of these things that looks like a piece of fruit is an atom.
00:20:24Without the tools of science, the machinery of life would be invisible.
00:20:33Four billion years ago, the ancestors of DNA were competing for molecular building blocks
00:20:39and leaving crude copies of themselves.
00:20:42There were no predators. The stuff of life was everywhere.
00:20:46So the oceans and the murky pools that filled the craters were, for these molecules, a garden of Eden.
00:20:53With reproduction, mutation, and natural selection, the evolution of living molecules was well underway.
00:20:59Varieties with specialized functions then joined together, making a collective, the first cell.
00:21:08The organic soup eventually ate itself up.
00:21:11But by this time, plants had evolved, able to use sunlight to make their own building blocks.
00:21:17They turned the waters green.
00:21:19A number of one-celled plants joined together, the first multicellular organisms.
00:21:27Equally important was the invention, not made until early November, of sex.
00:21:33It was stumbled upon by the microbes.
00:21:35By December 1st, green plants had released copious amounts of oxygen and nitrogen into the atmosphere.
00:21:46The sky is made by life.
00:21:49Then, suddenly, on December 15th, there was an enormous proliferation of new life forms.
00:21:57An event called the Cambrian Explosion.
00:21:59We know from the fossil record that life arose shortly after the formation of the Earth, suggesting that the origin of life might be an inevitable chemical process on countless Earth-like planets throughout the cosmos.
00:22:20But on the Earth, in nearly four billion years, life advanced no further than algae.
00:22:25Algae.
00:22:26So, maybe, more complex forms of life are harder to evolve.
00:22:31Harder even than the origin of life itself.
00:22:34If this is right, the planets of the galaxy might be filled with microorganisms.
00:22:40But big beasts and vegetables and thinking beings might be comparatively rare.
00:22:46By December 18th, there were vast herds of trilobites foraging on the ocean bottom.
00:22:57And squid-like creatures with their multicolored shells were everywhere.
00:23:01We know enough to sketch in a few of the subsequent details.
00:23:09The first fish and the first vertebrates appeared on December 19th.
00:23:13Plants began to colonize the land on December 20th.
00:23:16The first winged insects fluttered by on December 22nd.
00:23:19And on this date also, there were the first amphibians.
00:23:24Creatures something like the lungfish, able to survive both on land and in water.
00:23:30Our direct ancestors were now leaving the oceans behind.
00:23:33The first trees and the first reptiles evolved on December 23rd.
00:23:42Two amazing evolutionary developments.
00:23:47We're descended from some of those reptiles.
00:23:55The dinosaurs appeared on Christmas Eve.
00:23:59There were many different kinds of dinosaurs.
00:24:01The Earth was once their planet.
00:24:07Many stood upright and had some fair intelligence.
00:24:11Great lizards crashed and thundered through the steaming jungles.
00:24:21Unnoticed by the dinosaurs, a new creature, whose young were born alive and helpless,
00:24:26was making its timid debut.
00:24:28The first mammals emerged on December 26th.
00:24:32The first birds, on the following day.
00:24:38But the dinosaurs still dominated the planet.
00:24:42Then, suddenly, without warning, all over the planet at once, the dinosaurs died.
00:24:47The cause is unknown, but the lesson is clear.
00:24:51Even 160 million years on a planet has no guarantee of survival.
00:24:56The dinosaurs perished around the time of the first flower.
00:25:00On December 30th, the first creatures who looked even a little bit human evolved,
00:25:09accompanied by a spectacular increase in the size of their brains.
00:25:13And then, on the evening of the last day of the last month, only a few million years ago,
00:25:18the first true humans took their place on the cosmic calendar.
00:25:25The written record of human history occupies only the last ten seconds of the cosmic year.
00:25:30Now, let's take a closer look at who our ancestors were.
00:25:37A simple chemical circumstance led to one of the great moments in the history of our planet.
00:25:42There were many kinds of molecules in the primordial soup.
00:25:45Some were attracted to water on one side and repelled by it on the other.
00:25:51This drove them together into a tiny, enclosed, spherical shell, like a soap bubble, which protected the interior.
00:26:00Within the bubble, the ancestors of DNA found a home, and the first cell arose.
00:26:06It took hundreds of millions of years for tiny plants to evolve, giving off oxygen.
00:26:11But that branch didn't lead to us.
00:26:15Bacteria that could breathe oxygen took over a billion more years to evolve.
00:26:21From a naked nucleus, a cell developed with a nucleus inside.
00:26:27Some of these amoeba-like forms led eventually to plants.
00:26:35Others produced colonies, with inside and outside cells performing different functions.
00:26:41Others, becoming a polyp attached to the ocean floor, filtering food from the water.
00:26:51And evolving little tentacles to direct food into a primitive mouth.
00:26:57This humble ancestor of ours also led to spiny-skinned, armored animals with internal organs, including our cousin, the starfish.
00:27:09But we don't come from starfish.
00:27:11About 550 million years ago, filter feeders evolved gill slits, which were more efficient at straining food particles from the water.
00:27:21One evolutionary branch led to acorn worms.
00:27:25Another led to a creature which swam freely in the larval stage, but as an adult was still firmly anchored to the ocean floor.
00:27:33Some became living hollow tubes.
00:27:37But others retained the larval forms throughout the life cycle, and became free-swimming adults with something like a backbone.
00:27:45Our ancestors now, 500 million years ago, were jawless, filter-feeding fish, a little like lamp rays.
00:28:00Gradually, those tiny fish evolved, eyes and jaws.
00:28:05Fish then began to eat one another.
00:28:09If you could swim fast, you survived.
00:28:14If you had jaws to eat with, you could now use your gills to breathe the oxygen in the water.
00:28:19This is the way modern fish arose.
00:28:26During the summer, some swamps and lakes dried up, so some fish evolved a primitive lung to breathe air until the rains came.
00:28:33Their brains were getting bigger.
00:28:37If the rains didn't come, it was handy to be able to pull yourself along to the next swamp.
00:28:42That was a very important adaptation.
00:28:48The first amphibians evolved, still with a fish-like tail.
00:28:52Amphibians, like fish, laid their eggs in water where they were easily eaten.
00:28:56But then a splendid new invention came along, the hard-shelled egg laid on the land where there were as yet no predators.
00:29:04Reptiles and turtles go back to those days.
00:29:11Many of the reptiles hatched on land never returned to the waters.
00:29:15Some became the dinosaurs.
00:29:16One line of dinosaurs developed feathers useful for short flights.
00:29:21Today, the only living descendants of the dinosaurs are the birds.
00:29:26The great dinosaurs evolved along another branch.
00:29:31Some were the largest flesh-eaters ever to walk the land.
00:29:33But 65 million years ago, they all mysteriously perished.
00:29:40Meanwhile, the forerunners of the dinosaurs were also evolving in a different direction.
00:29:46Small, scurrying creatures, with the young growing inside the mother's body.
00:29:51After the extinction of the dinosaurs, many different forms developed.
00:30:00The young were very immature at birth, in the marsupials, the wombat, for example, and in the mammals.
00:30:08The young had to be taught how to survive.
00:30:11The brain grew larger still.
00:30:13Something like a shrew was the ancestor of all the mammals.
00:30:22One line took to the trees, developing dexterity, stereo vision, larger brains, and a curiosity about their environment.
00:30:31Some became baboons.
00:30:34But that's not the line to us.
00:30:37Apes and humans have a recent common ancestor.
00:30:41Bone for bone, muscle for muscle, molecule for molecule.
00:30:45There are almost no important differences between apes and humans.
00:30:52Unlike the chimpanzee, our ancestors walked upright, freeing their hands to poke and fix an experiment.
00:31:01We got smarter.
00:31:03We began to talk.
00:31:11Many collateral branches of the human family became extinct in the last few million years.
00:31:16We, with our brains in our hands, are the survivors.
00:31:22There's an unbroken thread that stretches from those first cells to us.
00:31:27Let's look at it again, compressing 4 billion years of evolution into 40 seconds.
00:31:32into 40 seconds.
00:31:33We'll see you in our hands.
00:31:34Here we go, it's seven minutes.
00:31:35We'll see you in the next few minutes.
00:31:37Let's look at it again.
00:31:41We'll see you in the next few minutes.
00:31:45We will see you in the next few minutes.
00:32:19Those are some of the things that molecules do given four billion years of evolution.
00:32:27We sometimes represent evolution as the ever-branching ramifications of some original trunk, each branch pruned and clipped by natural selection.
00:32:38Every plant and animal alive today has a history as ancient and illustrious as ours.
00:32:44Humans stand on one branch, but now we affect the future of every branch of this four-billion-year-old tree.
00:32:54How lovely trees are. The human species grew up in and around them.
00:33:04We have a natural affinity for trees.
00:33:07Trees photosynthesize. They harvest sunlight. They compete for the sun's favors.
00:33:17Look at those two trees over there, pushing and shoving for sunlight, but with grace and astonishing slowness.
00:33:27There are so many plants on the Earth that there's a danger of thinking them trivial, of losing sight of the subtlety and efficiency of their design.
00:33:44They are great and beautiful machines powered by sunlight, taking in water from the ground and carbon dioxide from the air and converting them into food for their use and ours.
00:33:58This is a museum of living plants, the Royal Botanic Gardens at Kew in London.
00:34:14Every plant uses the carbohydrates it makes as an energy source to go about its planty business.
00:34:27And we animals who are ultimately parasites on the plants, we steal the carbohydrates so we can go about our business.
00:34:35In eating the plants and their fruits, we combine the carbohydrates with oxygen, which as a result of breathing, we've dissolved in our blood.
00:34:50From this chemical reaction, we extract the energy which makes us go.
00:34:55In the process, we exhale carbon dioxide into the atmosphere, which the plants then use to make more carbohydrates.
00:35:02What a marvelous cooperative arrangement, plants and animals each using the other's waste gases.
00:35:11The whole cycle powered by abundant sunlight.
00:35:15But there would be carbon dioxide in the air, even if there were no animals.
00:35:20We need the plants much more than they need us.
00:35:23There are many family resemblances among the organisms of the earth.
00:35:32Some are very apparent, such as the use of the number five.
00:35:36Humans have five major bodily projections.
00:35:39One head, two arms, two legs.
00:35:42So do ducks, although the functions of their bodily projections are not quite the same.
00:35:48An octopus or a centipede has a different plan, and a being from another planet might be much stranger still.
00:35:57These family resemblances continue, and on a much deeper level, when we go to the molecular basis of life.
00:36:05There are tens of billions of different kinds of organic molecules.
00:36:12Yet only about fifty of them are used in the essential machinery of life.
00:36:17The same fifty employed over and over again, ingeniously, for different functions in every living thing.
00:36:24And when we go to the very kernel of life on earth, to the proteins that control cell chemistry,
00:36:31to the spiral or helix of the nucleic acids which carry the hereditary information,
00:36:38we find these molecules to be absolutely identical in all the plants and animals of our planet.
00:36:46This oak tree and me, we're made of the same stuff.
00:37:15If you go back far enough, you'll find that we have a common ancestor.
00:37:19That's why our chemistry is so alike.
00:37:25Let's take a trip to examine this common basis of life.
00:37:29A voyage to investigate the molecular machinery at the heart of life on earth.
00:37:35A journey to the nucleus of the cell.
00:37:39First, we need a cell.
00:37:41I have trillions.
00:37:43I can afford to donate a few.
00:37:46The casual act of pricking a finger is an event of some magnitude on the scale of the very small.
00:37:58Millions of red blood cells are detoured from their usual routes.
00:38:02But most continue to cruise about the body, carrying their cargos of oxygen to the remotest freckle.
00:38:13We're about to enter the living cell, a realm in its own way as complex and beautiful as the realm of galaxies and stars.
00:38:22Among the many red blood cells, we encounter a white blood cell, a lymphocyte, whose job it is to protect me against invading microbes.
00:38:31It makes antibodies on its furrowed surface, but its interior is like that of many cells.
00:38:37Plunging through the membrane, we find ourselves inside the cell.
00:38:44Here, every structure has its function.
00:38:50Those dark green blobs are factories, where messenger molecules are busy building the enzymes which control the chemistry of the cell.
00:38:59The messengers were instructed and dispatched from within the nucleus, the heart and brain of the cell.
00:39:06All the instructions on how to get a cell to work and how to make another are hidden away in there.
00:39:12We find a tunnel, a nuclear pore, an approach to the biological holy of holies.
00:39:18These necklaces, these intricately looped and coiled strands, are nucleic acids, DNA.
00:39:31Everything you need to know on how to make a human being is encoded in the language of life, in the DNA molecule.
00:39:38This is the DNA double helix, a machine with about 100 billion moving parts, called atoms.
00:39:55There are as many atoms in one molecule of DNA as there are stars in a typical galaxy.
00:40:02The sequence of nucleotides, here brightly colored, is all that's passed on from generation to generation.
00:40:13Change the order of the nucleotides, and you change the genetic instructions.
00:40:26DNA must replicate itself with extreme fidelity.
00:40:30The reproduction of a DNA molecule begins by separating the two helices.
00:40:35This is accomplished by an unwinding enzyme.
00:40:39Like some precision tool, this enzyme, shown in blue, breaks the chemical bonds that connect the nucleotides
00:40:46and bind the two helices of DNA together.
00:40:49The enzyme works its way down the molecule, unzipping DNA as it goes.
00:40:55Each helix copies the other, supervised by special enzymes.
00:41:03The organic soup inside the nucleus contains many free nucleotides.
00:41:07The enzyme recognizes an approaching nucleotide and clicks it into place, reproducing another rung in the double helix.
00:41:15When the DNA is replicating in one of your cells, a few dozen nucleotides are added every second.
00:41:25Thousands of these enzymes may be working on a given DNA molecule.
00:41:30When an arriving nucleotide doesn't fit, the enzyme throws it away.
00:41:46We call this proofreading.
00:41:48On the rare occasions of a proofreading error, the wrong nucleotide is attached,
00:41:52and a small random change has been made in the genetic instructions.
00:41:56A mutation has occurred.
00:41:58This enzyme is a pretty small molecule, but it catches nucleotides, it assembles them in the right order,
00:42:06it knows how to proofread.
00:42:08It's responsible in the most fundamental way for the reproduction of every cell and every being on Earth.
00:42:14That enzyme and DNA itself are molecular machines with awesome powers.
00:42:31Within every living thing, the molecular machines are busy making sure that nucleic acids will continue to reproduce.
00:42:39A minor cut in my skin sounds a local alarm and the blood spins a complex net of strong fibers
00:43:07to form a clot and staunch the flow of blood.
00:43:11There's a very delicate balance here.
00:43:13Too much clotting, and your bloodstream will solidify.
00:43:16Too little clotting, and you'll bleed to death from the merest scratch.
00:43:20The balance is controlled by enzymes instructed by DNA.
00:43:28Down here, there's also a kind of sanitation squad comprised of white blood cells
00:43:33that swings into action, surrounds invading bacteria, and ravenously consumes them.
00:43:40This mopping up operation is another part of the healing process, again controlled by DNA.
00:43:48These cells are parts of us, but how alien they seem.
00:43:52Within each of them, within every cell, there are exquisitely evolved molecular machines.
00:43:58Nucleic acids, enzymes, the cell architecture.
00:44:02Every cell is a triumph of natural selection.
00:44:06And we're made of trillions of cells.
00:44:09We are, each of us, a multitude.
00:44:14Within us is a little universe.
00:44:17Human DNA is a coiled ladder, a billion nucleotides long.
00:44:40Many possible combinations of nucleotides are nonsense.
00:44:45That is, they translate into proteins which serve no useful function whatever.
00:44:50Only a comparatively few nucleic acid molecules are any good for life forms as complicated as we are.
00:44:59But even so, the number of useful ways of assembling nucleic acids is stupefyingly large.
00:45:06It's probably larger than the total number of atoms in the universe.
00:45:11This means that the number of possible kinds of human beings is vastly greater than the number of human beings that has ever lived.
00:45:20This untapped potential of the human species is immense.
00:45:25There must be ways of putting nucleic acids together which will function far better by any criterion you wish to choose
00:45:32than the hereditary instructions of any human being who has ever lived.
00:45:39Fortunately, we do not know, or at least do not yet know, how to assemble alternative sequences of nucleotides to make alternative kinds of human beings.
00:45:51But in the future we might well be able to put nucleotides together in any desired sequence to produce whatever human characteristics we think desirable.
00:46:00A disquieting and awesome prospect.
00:46:04We human beings don't look very much like a tree.
00:46:19We certainly view the world differently than a tree does.
00:46:25But down deep, at the molecular heart of life, we're essentially identical to trees.
00:46:32We both use nucleic acids as the hereditary material.
00:46:37We both use proteins as enzymes to control the chemistry of the cell.
00:46:42And most significantly, we both use the identical code book to translate nucleic acid information into protein information.
00:46:53Any tree could read my genetic code.
00:46:57How did such astonishing similarities come about?
00:47:02Why are we cousins to the trees?
00:47:06Would life on some other planet use proteins, the same proteins, the same nucleic acids, the same genetic code?
00:47:15The usual explanation is that we are, all of us, trees and people, anglerfish, slime molds, bacteria, all.
00:47:26Descended from a single and common instance of the origin of life four billion years ago in the early days of our planet.
00:47:35Now, how did the molecules of life arise?
00:47:41In a laboratory at Cornell University, we mix together the gases and waters of the primitive Earth, supply some energy, and see if we can make the stuff we can do.
00:48:08But what was the early atmosphere made of? Ordinary air?
00:48:27If we start with our present atmosphere, the experiment is a dismal failure.
00:48:34Instead of making proteins and nucleic acids, all we make is smog, a backward step.
00:48:40Why doesn't such an experiment work?
00:48:43Because the air of today contains molecular oxygen.
00:48:46But oxygen is made by plants.
00:48:49It's pretty obvious that there were no plants before the origin of life.
00:48:53We mustn't use oxygen in our experiments because there wasn't any oxygen in the early atmosphere.
00:48:59This is perfectly reasonable because the cosmos is made mostly of hydrogen, which gobbles oxygen up.
00:49:09The Earth's low gravity has allowed most of our original hydrogen gas to trickle away to space.
00:49:15There's almost none left.
00:49:18But four billion years ago, our atmosphere was full of hydrogen-rich gases, methane, ammonia, water vapor.
00:49:26These are the gases we should use.
00:49:34Taking great care to ensure the purity of these gases, my colleague, Bishan Kari, pumps them from their holding flasks.
00:49:55An experiment like this was first performed by Stanley Miller and Harold Urey in the 1950s.
00:50:18The starting gases are now introduced into a large reaction vessel.
00:50:22We could shine ultraviolet light on this mixture, simulating the early sun.
00:50:27But in this experiment, the gases will be sparked, as the primitive atmosphere was, by early lightning.
00:50:34After only a few hours, the interior of the reaction vessel becomes streaked with a strange brown pigment.
00:50:39A rich collection of complex organic molecules, including the building blocks of the reactor.
00:50:44After only a few hours, the interior of the reaction vessel becomes streaked with a strange brown pigment.
00:51:02A rich collection of complex organic molecules, including the building blocks of the proteins and the nucleic acids.
00:51:11Under the right conditions, these building blocks assemble themselves into molecules resembling little proteins and little nucleic acids.
00:51:21These nucleic acids can even make identical copies of themselves.
00:51:28In this vessel are the notes of the music of life, although not yet the music itself.
00:51:39Now, no one so far has mixed together the gases and waters of the primitive Earth and at the end of the experiment had something crawl out of the flask.
00:51:55There's still a great deal to be understood about the origin of life, including the origin of the genetic code.
00:52:01But we've only been at such experiments for 30 years. Nature's had a 4 billion year head start.
00:52:08Incidentally, there's nothing in such experiments that's unique to the Earth.
00:52:13The gases we start with, the energy sources we use, are entirely common through the cosmos.
00:52:20So, chemical reactions something like these must be responsible for the organic matter in interstellar space,
00:52:27and the amino acids and the meteorites, similar chemical reactions must have occurred on a billion other worlds in the Milky Way galaxy.
00:52:36Look how easy it is to make great globs of this stuff.
00:52:40The molecules of life fill the cosmos.
00:52:45Now, what would life elsewhere look like?
00:52:50Even if it had an identical molecular chemistry to life on Earth, which I very much doubt,
00:52:56it could not be similar, very similar, in form to familiar organisms on the Earth.
00:53:03The random character of the evolutionary process must create elsewhere creatures very different from any that we know.
00:53:13Think of a world something like Jupiter, with an atmosphere rich in hydrogen, helium, methane, water and ammonia,
00:53:20in which organic molecules might be falling from the skies like manna from heaven,
00:53:25like the products of the Miller-Urey experiment.
00:53:28Could there be life on such a world?
00:53:31Well, there's a special problem.
00:53:33The atmosphere is turbulent, and down deep, before we ever come to a surface, it's very hot.
00:53:39If you're not careful, you'll be carried down and fried.
00:53:42So one way to make a living is to reproduce before you're fried.
00:53:46Turbulence will carry some of your offspring to the higher and cooler layers.
00:53:51Such organisms could be very little.
00:53:53We call them sinkers.
00:53:57The physicist E.E. Saul Peter and I, at Cornell,
00:54:00have calculated something about the other kinds of life that might exist on such a world.
00:54:05Vast, living balloons could stay buoyant by pumping heavy gases from their interiors,
00:54:15or by keeping their insides warm.
00:54:17They might eat the organic molecules in the air, or make their own with sunlight.
00:54:22We call these creatures floaters.
00:54:27We imagine floaters kilometers across, enormously larger than the greatest whale that ever was.
00:54:32Beings the size of cities.
00:54:36We conceive of them arrayed in great lazy herds as far as the eye can see.
00:54:43Concentrated in the updrafts, in the enormous sea of clouds.
00:54:48But there can be other creatures in this alien environment.
00:54:50Hunters.
00:54:54Hunters are fast and maneuverable.
00:54:56They eat the floaters, both for their organic molecules and for their store of pure hydrogen.
00:55:01But there can't be many hunters.
00:55:03Because if they destroy all the floaters, they themselves will perish.
00:55:12Physics and chemistry permit such life forms.
00:55:15Art presents them with a certain reality.
00:55:18But nature is not obliged to follow our speculations.
00:55:21However, if there are billions of inhabited worlds in the Milky Way galaxy,
00:55:27then I think it's likely that there are a few places which might have hunters and floaters and sinkers.
00:55:35Biology is more like history than it is like physics.
00:55:42You have to know the past to understand the present.
00:55:45There's no predictive theory of biology just as there's no predictive theory of history.
00:55:49The reason is the same.
00:55:51Both subjects are still too complicated for us.
00:55:53But we can understand ourselves much better by understanding other cases.
00:56:01The study of a single instance of extraterrestrial life,
00:56:05no matter how humble a microbe would be just fine,
00:56:09will de-provincialize biology.
00:56:11It will show us what else is possible.
00:56:17We've heard so far the voice of life on only a single world.
00:56:22But for the first time, as we shall see,
00:56:25we've begun a serious scientific search for the cosmic fugue.
00:56:41In recent years, we've learned much more about the origin of life.
00:56:46Do you remember RNA, that nucleic acid that our cells use as messengers
00:56:51carrying the genetic information out of the cell nucleus?
00:56:55Well, it's been found that RNA, like protein, can control chemical reactions,
00:57:02as well as reproduce itself, which proteins can't do.
00:57:06Many scientists are now wondering if the first life on Earth was an RNA molecule.
00:57:11And it now seems feasible that key molecular building blocks for the origin of life
00:57:17fell out of the skies four billion years ago.
00:57:20Comets have now been found to have a lot of organic molecules in them.
00:57:24And they fell in huge numbers on the primitive Earth.
00:57:29We also mentioned the extinction of the dinosaurs,
00:57:33and most of the other species of life on Earth about 65 million years ago.
00:57:36We now know that a large comet hit the Earth at just that time.
00:57:41The dust pall from that collision must have cooled and darkened the Earth,
00:57:46perhaps killing all the dinosaurs, but sparing the small, furry mammals who were our ancestors.
00:57:53Other cometary mass extinctions in other epochs seem likely.
00:57:59If true, this would mean that comets have been the bringers both of life and death.
00:58:04And death.
00:58:05And death.
00:58:06And death.
00:58:07Find the sound of her mind, human being white.
00:58:10Somehow they have shot it as a helicopter.
00:58:11We might see how many of them are living in life.
00:58:12Watch them as if pain moving intoack that!
00:58:14But that's why they're confident that they're used to touch more than walking wise.
00:58:17And no idea that Kim makes white.
00:58:19They've hard at Shout attention to Srivivalびs Granddad.
00:58:22The nation Himself still is now looking!
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