In the second episode of Cosmos, Neil DeGrasse Tyson tackles the greatest story science has ever told: the story of life.
Tyson begins with the evolution of dogs from wolves via artificial selection, or if you prefer, the domestication of humans by dogs. Wolves that were friendlier, tamer and more loyal to humans were selectively bred to be our companions. As we settled into agricultural communities in the break between ice ages, dogs became the partners of our labors, consuming and burying our trash, defending our territory and helping us hunt.
"Artificial selection turned the wolf into the shepherd," Tyson tells us before asking the question that has inspired battles in courtrooms and classrooms since Darwin first posed it in 1859: "If artificial selection can accomplish that much in just a few thousand years, what can natural selection accomplish given billions of years?"
In the Ship of the Imagination, Tyson takes us on a fantastic voyage through the genetic code of the ice age bears who gave rise to modern polar bears in a process he calls "the opposite of random." He confronts the "twinge of discomfort" some might feel at the suggestion we are related to the apes: "No one can embarrass you like a relative." Of course, it's not just the apes. The genes in our body that digest sugar are identical to the genes used by plants and insects. And so is each species on Earth is arranged on a gigantic family tree, a literal tree of life.
To challenge the notion that life is simply too complex to have arisen out of an undirected process like natural selection, Tyson selects one of the favorite chew toys of special creation: the human eye. How is it possible for something so, you will forgive the phrase, irreducibly complex as the human eye to have arisen from natural selection alone? The story of the eye is told in a split screen, with the stages of ocular development shown on the left and the visual field of the eye on the right. With each generation, slight improvements in eye structure result in images that become clearer and clearer.
By connecting small changes in morphology to large improvements in performance, Tyson illustrates the inconvenient truth for those who insist the eye must be designed: everything about the eye, and indeed the rest of our bodies, shows evidence of incremental improvement occurring over multiple generations, not special creation occurring in one generation. Nothing in biology makes sense in light of any other explanation.
In the final segment, Tyson describes the five major extinction events that threatened life on Earth, with special attention to the Permian event, and the role of extremophiles in preserving the tree of life against catastrophe. He then visits Titan in the Ship of the Imagination and wonders what kind of life could survive in a world of liquid methane seas and frozen water mountains.
Tyson finishes the episode by replaying Carl Sagan's original 40-second line-animated history of life on Earth. This callback to Sagan's original program highlights the power that modern visual effects have brought to Cosmos. More than anything else, the story of life is a visual story, a story of bodies emerging and re-merging, changing shape and passing those shapes down through the eons.
Sagan's take may well be the more poetic, but the more literal modern graphics of Tyson's Cosmos show us that this is not myth or fanciful imagining, not simply a narrative we tell ourselves about the development of life or a mere opinion. Tyson tells us that evolution is a theory, but what science means by theory is fact. It happened. It's as real as gravity. It can be described literally and now rendered literally.
In this episode of Cosmos, we truly see what Sagan called "some of the things molecules can do, given a billion years of evolution."
Cosmos airs on Sunday nights at 9:00 on Fox and Monday nights at 10:00 on the National Geographic Channel