Cosmos: A Spacetime Odyssey Recap - Episode 102

"Some of the Things that Molecules Do"

Episode 2 of Cosmos dealt with DNA and evolution
Cosmos: A Spacetime Odyssey (ep 102). FOX Broadcasting

 Note:  This is a recap for episode 102 entitled "Some of the Things that Molecules Do". You can read the episode 101 recap here.

This week’s episode starts off with our fearless leader, host Neil deGrasse Tyson, all bundled up in the woods at a campfire talking about how dogs didn’t exist at one point in time.  Now there are tons of different kinds of dogs.  Where did all of these different kinds of dogs, and really all the different living things on Earth, come from?

 Tyson tells us it’s a great power that sounds like a myth, but it’s not.

After a visually stunning opening credits with a grand musical score, we’re back to our beloved host in the woods who says we’re going back 30,000 years to when our wandering ancestors were living in the last ice age.  They used the sky to predict weather, harvest times, and other things that would help them survive.  However, they still lived in fear as they camped out under the stars because there were hungry bears and mountain lions among other creatures that could harm them.  

A wolf comes up behind Tyson, and he scares it off with a piece of wood lit on fire.  He then throws the leftovers from his dinner out to the side and tells the audience all of the wolves around him want to eat the bone, but they do not come close because they have stress hormones coursing through them since they are scared of humans and know they could be killed.

 However, a few wolves once had a natural variation that made them less afraid of humans.  

Evolution of Dogs

15,000 years ago, some of these wolves figured out that if they didn’t threaten the humans, the humans would do the hunting for them and they would be safe and eat well.  This domestication allowed them to survive longer to leave offspring that had the same disposition.

 The wild wolf line diverged and evolved into dogs. This also benefited the humans because the dogs not only cleaned up their leftovers, they also became a security detail for the human ancestors. Another trait that evolved in dogs is cuteness.  The cuter the dog, the more likely it was to be adopted by a human.

A cartoon depiction then shows a more recent human ancestor.  These people have settled into a community instead of continuing to wander endlessly.  The slight break in the ice age weather has allowed them to set up a camp where they could stay in villages.  They invented agriculture and could produce clothing.  

The wolves have become domesticated in exchange for food. They no longer get to choose their own mates because they humans do it for them. If the wolves couldn’t be trained, they were killed off and only those fully domesticated survived to have offspring after being bred to other wolves with similar dispositions. Dogs evolved through artificial selection and humans have been helping control evolution of other species ever since then. It only took 15,000 to 20,000 years to turn a gray wolf into all of the dog breeds we see today.

All of a sudden, we are back on the Cosmos “Ship of the Imagination” from last week’s episode.

 Tyson tells us that almost everything we eat today was created by artificial selection from a less tasty plant or animal. So if artificial selection by humans can cause all that diversity in a relatively short amount of time, what could natural selection do over billions of years?  His answer: everything. All of the diversity we see is a culmination of billions of years of natural selection driving evolution.

Evolution of Bears

When we return from commercial break, Tyson tells us that we’ve been living in an ice age for the last 2 million years. We just happen to be in an “intermission” of sorts right now where the climate is cold and dry.  The winter sea ice used to stretch from the North Pole down to where Los Angeles is today.  Bears once roamed freely on this expansive ice cap.

The next thing we know, we’re traveling on the Ship of the Imagination down to a cellular level and into the bear’s reproductive system.

 The ship shrinks to the molecular level as it enters the bear’s eggs and Tyson tells us we are now at a size where a grain of sand would hold a million of our ships. He points out proteins called kinesin that help move things around the cell. Every living cell has them. The ship moves into the nucleus where the DNA is kept.

All life has the same DNA “language”. It’s a molecule shaped like a twisted ladder, otherwise known as a double helix.  The “rungs” of the ladder are made up of what Tyson calls the four “letters of the genetic alphabet” that spell out instructions for living things and all of the processes they undergo.There are as many atoms in a single molecule of DNA as stars in a typical galaxy.

The DNA message is copied very carefully.  First, the molecule is untwisted and broken apart by a protein. The genetic code letters float freely around in the liquid part of the cell.  Each strand of DNA finds the right partner for its code and each strand makes a new partner strand for itself.  This happens before the cell splits in two so each new cell will get an exact copy of the DNA. There is a special protein that proofreads and makes sure there are no mistakes, but every now and then a mistake will sneak by and a mutation has occurred.  Tyson points out a mistake that has been made in the bear’s egg cell that could have consequences on a very large scale.

We then see some animated bears and Tyson tells us the mutation in the bear’s egg cell has led to a loss of the darker pigments in the bear’s fur.

 Most mutations are harmless, some are deadly, and a few can give an organism an advantage over its competition. The bear that had the mutation in her eggs has given birth to two cubs.  One has the newly mutated white fur, and the other is a normal brown color.  The white bear is able to be hidden better in the snowy environment and it is able to sneak up on prey more easily. This allows it to thrive and pass down its white fur gene to its offspring while many dark colored bears die off.  Eventually, the entire population of arctic bears are white.

Mutations are random and happen all the time. The environment naturally selects those who are better suited to survive there. Over time, more differences will happen in the bear population. They become different species.  This is what Charles Darwin meant by the “Origin of Species”. An individual will not evolve, but the population will.

If the polar ice caps keep melting, the polar bears will go extinct and will be replaced by brown bears that have adapted to the warmer climates. This is evolution by natural selection and not artificial selection. Darwin proposed this in 1859, but the “uproar” over the idea has not gone away. Tyson asks, “why?”

The Controversy of Evolution

When we get back from commercial, Tyson jumps right into why human evolution is controversial. He likens it to feeling embarrassed by our relatives. Our closest living relative is the chimpanzee and Tyson points out they don’t always act properly in public. There is a need to distance ourselves from them to make us feel special. It is easier to just believe we were created separately than to think we share a common ancestor.

Tyson then asks how does it make you feel that we are also related to trees?

We look into the oak tree’s DNA and then compare it to Tyson’s own DNA and it shows we have the same codes for processing sugars. It means that humans and trees are what Tyson describes as “long lost cousins”.  He then says we share a common ancestor with butterflies, wolves, mushrooms, sharks, bacteria, and sparrows. Differences in a few parts of the DNA sequence are what make species different from each other.  In fact, everyone has unique DNA sequences (unless you are an identical twin). These differences provide the raw materials for natural selection to work on.

The Tree of Life

All living things have the same instructions for life’s basic functions in their DNA. Things like how to digest sugar evolved long before the different species branched off of the tree of life from each other. Closely related species are on the same branch of the tree of life and each species is its own individual twig.

Distantly related species occupy other branches of the tree.  The trunk is the common ancestors of all life.

Tyson tells us the tree of life is much bigger than what can be shown here.  Biologists have catalogued over half a million different kinds of beetles alone.  There are also large amounts of different types of bacteria.

We haven’t even found many of the terrestrial species out there yet. Changes in the environment allow new species to appear on the tree of life. This diversity was started over three and a half billion years ago. Evolution can disguise animals as plants so they can fool predators. It can also create plants that look like animals so they will be pollinated.

Humans are one tiny branch among millions of the tree of life.  Darwin discovered the mechanism that caused evolution. At the time, the prevailing thought was that there must be an intelligent designer that created all species separately because life was too complex for it work naturally.  For example, take the human eye. It is too intricate. It takes an iris, lens, retina, optic nerve, muscles, and the brain among other parts to work. It was too complex to have just appeared on its own. We jump back on the Ship of Imagination to see if this assumption is true.

Evolution of the Human Eye

When we return from the break, we have traveled back to the beginning of life on Earth. All of life on Earth was just bacteria.  One of those bacteria acquired a mutation that allowed it to absorb sunlight. It was now a light sensitive bacteria. This phenomenon is shown as a split screen that shows what the bacteria’s point of view would have looked like compared to a human’s.

Another mutation would cause dark bacteria to move away from intense light. The bacteria that could detect light had an advantage as they could flee the harsh ultraviolet light while others could not.

They continued to evolve and eventually these light sensing areas were concentrated on a spot of pigment making it possible to find the light and use it to make food. Eventually, a “dimple” evolved in the light spot and the organisms could then detect light from shadows and make out some objects in the vicinity including predators and prey. This evolved into a socket and over thousands of years natural selection continued to sculpt the eye.

An opening could close to the size of a pinhole and it was covered by a protective membrane to control how much light could get in and it sharpened the image.

A lens came into existence next from the gel that was by the pinhole. It allowed not only a more sharp focus, but also allowed in more light for a brighter picture. Then the pinhole enlarged to let in more light. The creatures could now see in high definition both close up and far away. The split screen shows nearly an identical picture on both sides as what we can see and what those fish could see.

Then something terrible happened, Tyson tells us. As life moved to land, their eyes that had evolved for living in the water were not as good on land due to the refraction of light. Tyson tells us our eyes have not been as good ever since then. 75 million years later, we still can’t see in the dark or the very small details in front of us like the fish can. So why didn’t nature evolve us a new set of eyes? Tyson explains that evolution can only adapt what is there and cannot start from scratch. We can see all of the stages of development in the eye in various species living today.

Tyson then gets into the argument that some people have about evolution being “just a theory” like it is an opinion.  He says that the theory of evolution, like the theory of gravity, is fact. Evolution really happened and accepting it is solid science. Evolution is blind and can’t anticipate catastrophes. Some of the trees of life were broken during the “five greatest catastrophes life has ever known.”

Mass Extinctions

The next segment starts by Tyson leading us into the “halls of extinction.” He calls it a monument to the broken branches of the tree of life.

There are millions of species alive today, and Tyson tells us that for every one of them, there are maybe a thousand others that have gone extinct. Most died from competition, but others died from one of the five mass extinction events that devastated life on Earth. The largest one happened 250 million years ago at the end of the Permian Period.

Trilobites were among the first animals to evolve eyes. They lived 270 million years and pretty much ruled the Earth.  They are extinct now because of an unparalleled environmental disaster. It began in Siberia with volcanic eruptions beyond compare. Earth was very different then with one supercontinent and one big ocean. The volcanic eruptions covered an area larger than all of Western Europe. This went on for hundreds of thousands of years polluting the air with carbon dioxide and other greenhouse gases. The Earth heated up and the ocean currents stopped circulating. Almost everything in the sea died and noxious sulfur dioxide gases suffocated nearly all land animals. 9 out of 10 species on Earth went extinct. This time was known as the “great dying.”

It took more than 10 million years to recover, but new species evolved to fill the gaps left from this mass extinction. The dinosaurs thrived for about 150 million years until they too went extinct from another of the catastrophic mass extinction events. Earth has taken a beating over all of Geologic Time, but life continues to bounce back. In fact, we keep finding life in places we didn’t think anything could live.

Life has been found in boiling water and solid ice. There are even life forms that can go without water for years. The tardigrade, or water bear, is a life form that can live anywhere from the highest mountains to the deepest trenches in the sea, or even your backyard. They are only about the size of a pin point, so they go unnoticed for the most part. They are the toughest life form on the planet and have survived all five mass extinctions and lived for half a billion years. They have shown us that life isn’t as picky and fragile as we once thought and it can live in all kinds of places we never thought possible.

Life Outside of Earth

What would life be like on other planets that have a different chemical make up than our own? Tyson takes us on a journey to Saturn’s giant moon Titan. Its hazy atmosphere has no oxygen and it’s far colder than anywhere on Earth. Beneath the smog of Titan is a landscape that is not too much different that what we would see in places on Earth.  

It is the only other land in our solar system that rains and has rivers and coastlines. It also has hundreds of lakes. One of these lakes is bigger than Lake Superior and as it evaporates, it rains back down into rivers that carve out canyons just like on Earth. However, these bodies are not made of water, but of methane and ethane.

The cold climate of Titan turns what would normally be gas on Earth into liquid methane. Titan does have water, but it is frozen solid. Still, it may be possible that life could be found on Titan. It would be much different than our water based life forms, possibly breathing in hydrogen instead of oxygen or using other chemicals instead of sugars for fuel.

How would we find out if such life exists? Tyson pilots the Ship of Imagination into the oil dark Kracken Sea on Titan. He tells us, even if there was a Kracken in the sea, we wouldn’t be able to see it because it is so dark. All of the oil and natural gas on Earth is just a tiny fraction of what Titan has in its reserves.

History of Life on Earth

Tyson says there is one last story he wants to tell and it’s the greatest story ever told. It’s the story of life on our planet. We start at the beginning of the Earth four billion years ago before life. No one knows how life was started and most of the evidence was destroyed by impacts over time. Science is not ashamed to admit there are things we don’t know. The only shame is to pretend that we have all the answers and maybe someone watching the program will be the first to solve the mystery of how life began.

The evidence from living species of microbes suggests life first started in extremely hot water near volcanic vents in the ocean. Tyson tells us that in the original Cosmos series with Carl Sagan, he traced the entire history of life from four billion years ago to the present day humans in 40 seconds. That 40 second clip then plays from the original series with illustrations starting at bacteria and going through lower life forms and up through humans to end the show.

 

 

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Scoville, Heather. "Cosmos: A Spacetime Odyssey Recap - Episode 102." ThoughtCo, Jan. 3, 2018, thoughtco.com/cosmos-a-spacetime-odyssey-recap-102-1224638. Scoville, Heather. (2018, January 3). Cosmos: A Spacetime Odyssey Recap - Episode 102. Retrieved from https://www.thoughtco.com/cosmos-a-spacetime-odyssey-recap-102-1224638 Scoville, Heather. "Cosmos: A Spacetime Odyssey Recap - Episode 102." ThoughtCo. https://www.thoughtco.com/cosmos-a-spacetime-odyssey-recap-102-1224638 (accessed January 17, 2018).