Campfires are where we tell stories: ghost stories, myths, tall tales, fables, and jokes. In the second episodes of Cosmos, Neil DeGrasse Tyson starts us off with a shaggy dog story, literally. “There was a time, not long ago, before dogs,” he says. “They didn’t exist. Now there are big ones, small ones, snugglers, guardians, hunters, every kind of dog you could possibly want. How did that happen?“
If you guessed “evolution,” you would get only partial credit, for the diversity within the species Canis lupus, which includes dogs, wolves, and dingoes, owes to a particular type of evolution—artificial selection, rather than natural selection.
Dogs, to answer Tyson’s question, came from wolves, their closest cousins. Wolves can get freaked out if they venture too close to a campfire, but some, through natural variation, had lower levels of stress hormones and were relaxed enough to hang out and make s’mores with our Ice Age ancestors. While the other wolves were left asking “s’more of what?” these wolves, able to come close to the human kitchen, began to eat more regularly and therefore left more offspring, passing on their cheerful disposition. “This selection for tameness would be reinforced with each generation,” Tyson says, “until that line of wolves evolved into dogs. You might call this survival of the friendliest,” he says as a whimpering Rottweiler enters the frame.
After dogs, humans learned to artificially select other species: corn, chickens, marijuana, Brassica oleracea. It’s impossible to deny the influence we’ve had over these species and we’ve done it in so short of a time. In less than 20,000 years we’ve turned gray wolves into greyhounds. “If artificial selection can work such profound changes in only ten or fifteen thousand years, what can natural selection do operating over billions of years?”
For those of us waiting to see how long it would take for Cosmos to take on evolution, the answer is “not long” and it’s done in brilliant fashion. Familiar, diverse and cuddly, dogs are the perfect way to introduce core ideas such as selection and differentiation. Fundamentalist Christians (and Muslims, among others) like to tell their own campfire stories about how we came to be, so for them this will be Tyson’s own special episode of “Are You Afraid of the Dark?” but with darkness replaced by truth.
From here we take on “all the beauty and diversity of life,” the result of natural selection. To see the effects of just a single genetic change and how nature can select for it, our spaceship of the imagination drops in on a pregnant mama bear during the last ice age. Didn’t think you’d be visiting bear ovaries today, did you? Inside the ovaries are eggs, and inside the eggs is the DNA of the next generation of bears. The script of life, DNA is a molecule, and these molecules are subject to review under the processes of biochemistry. The particular arrangement of the chemical letters of DNA is subject to random changes. With a pretty nifty mechanical DNA unzipper/copy machine, we see how errors in proofreading can lead to a mutation. It’s a tiny random event—many changes are harmless though some are deadly—but when it affects something like fur color, it can mean big things for baby bear.
Not only do we get to see where the first dogs come from in this episode, we also get to see where the first polar bears come from in this episode, which is good, because we may soon be seeing the last polar bears in real life. As a ninja embraces the shadows, our new bear with the white fur mutation embraces the blinding white of the ice sheet. The seals don’t stand a chance and as baby bear becomes a mama bear of its own, the gene for white fur propagates through the population of Arctic bears, while brown loses out. Nature has spoken, rewarding genes that increase the chances of survival. And if climate change melts the ice at the North Pole, erasing the polar bears’ advantage? You guessed it, bye bye bears. So if you want to see polar bears outside of Coca-Cola commercials, it may be time to do something about it.
Ok, you may be thinking, fur is great, but what about something more complex? How does something like the eye evolve? It’s a great question that deserves an explanation. It’s also a question that people more interested in perpetuating an ideology, like proponents of “intelligent design” use to try and confuse those of us who haven’t studied the evolutionary history of the eye.
Well, since you mention it, Ann Druyan has pieced together a plausible natural history of the eye. There’s no way to be certain, but it’s good enough to seriously hoist the intellectual design movement’s own petard up by its underpants. Call it a brain wedgie, if you like.
But before we get to the eye, we first have to think about trees. It turns out that humans and oak tress share the same DNA when it comes to the proteins needed to metabolize sugars. Sparrows, mushrooms, and bacteria all have sections of their DNA in common with each other and with us. The genes for digesting sugars and other basic necessities for life evolved before we all branched off from each other. “The stuff of life is so malleable that once it got started, the environment molded it into a staggering variety of forms. There are half a million kinds of beetles alone, not to mention what might as well be an uncountable number of bacteria. We have yet to discover most of the different forms of life on this planet alone.
Evolution can disguise an insect as a tree to deter predators and a flower as a wasp to encourage pollination. “This is the awesome shape shifting power of natural selection,” Tyson says.
“Science reveals that all life on earth is one.” In many ways, we are lucky that Darwin was as good a scientists—and good a writer—as he was. The “tree of life” is a perfect metaphor and Cosmos takes full advantage of this visually. This tree of life is massive, with numerous branches, a fitting a monument to evolution by natural selection.
OK, now on to the eye. The human eye—and the octopus eye for that matter—are extremely complex organs. Cornea, lens, iris, retina, and optic nerve have to combine to create images for the brain to process. Too complex, especially to happen twice, driven by mindless evolution, or so you may be led to believe.
But what if it were the result a series of changes that started small and increasingly gave the organisms that had acquired them a slightly better chance at survival?
Throughout this entire sequence, we’re often given a split screen, to see a visualization of what the creature might “see” with this hypothetical proto-eye.
Let’s first consider single celled organisms in the early seas. Out of the blue, one of these suddenly is now carrying around a light sensitive protein in it. Throw in a random mutation for that organism to flee intense light and we are off. Sunlight, as you can ask anyone with melanoma, can be as dangerous as it is comforting. The high-energy ultraviolet rays that damage DNA which sometimes leads to fatal mutations.
Fast-forward a couple million generations and now we find that those light sensitive proteins have collected together into a pigment spot. Seems plausible. If the organisms evolving this trait were photosynthetic algae, the ability to find the light would give them a huge advantage in the oceans, where sunlight quickly loses strength with depth. Adding in a dimple in the pigment spot would allow a more advanced organism to distinguish light from shadow a crude representation of objects in its vicinity. Deepen the dimple and add a small opening and you’ve got nature’s first camera obscura. Throw on a membrane to protect the sensitive surface of the socket and later muscles to control the size of the opening and now we’ve got something that adds focus to the picture. “This launched the visual equivalent of an arms race,” Druyan writes.
If you let the membrane evolve into a lens in this configuration, it allows for both brightness and focus. The hole doesn’t have to be as small so it can open up to let in more light. We’re now swimming with the fishes that can see objects both close up and far away. Finally, filling the eye with fluid helped adjust for the different ways that light behaves when travelling through air and water.
However, this fluid filled eye wasn’t so good once life moved up onto land. But we can’t start over with a visual system optimized to see through air, evolution can only improve upon what it already knows. “At every stage of its development, the evolving eye functioned well enough to provide a selective advantage for survival. And among animals alive today, we find eyes at all these stages of development. And all of them function,” Tyson says. “The eye, and all of biology makes no sense without evolution.” Evolution is a scientific fact, Tyson says emphatically looking directly into the camera. If Quentin Tarentino had been directing this episode, Tyson’s line might have been, “Say ‘evolution is only a theory’ again I dare ya, I double dare ya, motherfucka. Say ‘evolution is only a theory’ one more goddam time.
Thankfully, Tyson appeals not to fear but to revelation. “Accepting our kinship with all life on earth is not only is it solid science, it’s a soaring spiritual experience.”
Among those kin are dead relatives though, “broken branches” on the tree of life. Tyson takes us to the mausoleum of the lost species, many which died out in one of five (or six, if you accept that we’re living through one right now) mass extinctions. The worst of these was the Permian extinction, which happened 250 million years ago. Trilobites had ruled the seas for over 270 million years but aren’t around any longer, wiped out by an environmental disaster. Volcanic activity over thousands of years ignited coal deposits, flooding the atmosphere with carbon dioxide and greenhouse gases, heating the earth and stopping ocean currents dead. Bacteria bloomed, but almost everything else died. Nine out of every ten species on the planet died.
It took almost ten million years before new life forms started evolving, like the dinosaurs, but we all know how that ended.
“Life has taken a quite beating over the eons and yet it’s still there,” Tyson says. “The tenacity of life is mindboggling. We keep finding it where no one though it could be.”
The hardest creatures to kill are not cockroaches, or drug resistant bacteria, or even Rasputin, but tardigrades, microscopic creatures also known as water bears. They’re kind of cute, even if they look like a sea cucumber with eight legs and claws. A tardigrade can survive, freezing, boiling, desiccation and even the vacuum of space. None of the five mass extinctions has been able to wipe them off the face of the Earth. Who knows, maybe they’ll never leave.
If the tardigrades can survive the vacuum of space, surely life could exist elsewhere in the universe, right? To find out, we go not too far away to Saturn’s moon Titan. Though Titan has an atmosphere that’s mostly nitrogen, it has no oxygen and is much denser. And while it’s much, much colder than even Canada, it has rain, rivers, lakes and seas, just like Earth. But while we have liquid water, Titan has liquid methane. Could life swim in Titan’s hydrocarbon lakes? Might they inhale hydrogen and exhale methane? Sadly, even trip down to an undersea vent in the spaceship of the imagination reveal anything.
Similar vents here on Earth may have been the first home of life on Earth, as evidence from bacteria indicates their ancestors like high temperatures. From those single celled organisms have grown an entire tree of life.
The episode ends with another call back to the original Carl Sagan cosmos, an animation of a possible path from bacteria to human beings, showing the continuity of life, just one of the things the molecules do.