Tyson starts with dogs. Yes, dogs. We've all seen dogs and their many varieties. Especially kids. So Tyson starts with the simple questions: where did dogs come from? And why are there so many different kinds? Well, Tyson goes back about 30,000 years ago, during the last Ice Age, when human groups produced a large amount of food scraps. Most wolves "knew" better than to get to close to human groups. Tyson explains this as a hormonal response to situations that could be dangerous. The more hormones a given wolf produced near humans, the more distance that wolf would keep from humans. However, wolves with low stress hormones from fear would approach human groups and feast on the food scraps. Over time, these friendly wolves would protect their easy food source. Over time, human generations chose puppies for their cuteness, and bred older dogs for their obedience and work skills. Human breeding, or artificial selection, produced all the breeds we know and scoop poop for today. Tyson also points out that agricultural development is the same principle; we selected wild plants for food, discovered how to grow it ourselves, and kept seeds to grow future generations from the best food-producing plants.
Tyson then draws the distinction between artificial and natural selection. Artificial selection may be faster, but is totally under the control of a conscious mind. Natural selection is totally out of humans' control, and works over billions of years and millions of generations of living things, and has no desired end goal. Natural selection is driven by an organism's natural environment; artificial selection is driven by the desires of one species over another.
Tyson, after going through a little geological history, shows how natural selection produced polar bears. But first he starts by pointing out that he's about to get really small, because it turns out that microscopic proteins at the molecular level are driving the process by which life works. Tyson plays with scale to make the point that the very small can affect entire generations of huge animals. By showing how proteins make the instructions for building a living thing, DNA, Tyson also explains how cells divide and multiply. In most cells, including sex sells, a protein actually checks to make sure dividing cells' DNA codes are identical to the original. There's an occasional typo, though, which Tyson defines as a mutation. That mutation could result in a unnoticed change. It can also develop into a change which either helps or hinders that organism in its environment. Keep in mind, a bad mutation in one environment could be beneficial in another. It's the combination of environment and mutation that produces evolutionary change.
shit's gettin' real here in the DNA
Tyson shows how beneficial mutations give one organism an edge in some survival skill, such as a white bear on a polar ice cap. That beneficial mutation, being genetic, gets passed on. Organisms that didn't have the mutation don't reproduce as much. Over generations, the white bears' numbers increase in the bear population, while less well-evolved bears' numbers decrease. Other mutations get added to the mix, also either getting passed on or not. As generations keep producing slightly genetically different bears, the genetic differences keep adding up, until one generation is so genetically different from the original it mutated from, that another species has officially been born.
History Maker, Innovator, Genome Radical
Tyson explains how Darwin introduced our understanding of evolution, and describes the main controversy from people who refuse to accept evolution: too someone who prefers to be separate from nature, evolution and our relatedness to other animals takes away our specialness as humans. So Tyson introduces the tree of life, describing how our relatedness to other animals, plants and even bacteria resembles a tree with branches. The closer to the trunk, the older the species with more mutated descendants. An awesome, bushy oak tree springs up, with animal representations. Clearly, Tyson wants us to appreciate being connected to the world we live in, not demand that we be fundamentally different from it. The forms of life today, their shapes and abilities, represent the histories of biology, geology and climate on this Earth. That's pretty impressive, even if a supernatural explanation for life would make you feel a connection to the immortal.
Tyson then goes on to describe the idea that's supposed to replace evolution: intelligent design. Tyson describes that some people believe living things have too many complex pieces, and those complex pieces could not have evolved from natural selection. Tyson then crushes one of ID's first examples of these pieces, that are supposed to be irreducibly complex: the eye.
Tyson goes into a great set piece starting with early bacteria and describing the beginnings of sight, starting with mutated proteins that formed light sensitive patches that enabled early bacteria to avoid sunlight and reproduce mightily in darker waters. These light patches became depressions, where light could then be coupled with shadows, for the beginnings of making out form. Along the way, he shows the living thing with a new piece of the puzzle next to how it would have 'seen' the world. Bit by bit, each piece of the eye developed from something else, with the complexity that that particular organism needed. As organisms became more complex, so did their eyes. One big drawback of natural selection on our eyes? Land animals have had to adapt their eyes ever since leaving the water, since eyes initially developed to see in water. We've kind of gotten the shaft of visual evolution.
There's only one situation where evolution can't help living things: with sudden environment changes. Tyson explores our planet's mass extinctions, putting them in context and explaining the catastrophe called the Permian Mass Extinction, or the Great Dying, when 90% of the world's living species died out, including the trilobytes, the ubiquitous Permian life form.
Combination underwater bug and fish. Gross, but effective.
He explains that it started in what we would call Siberia today, when the world had one super-continent with oceans surrounding. Volcanic eruptions without end started a chain reaction that affected worldwide temperatures and atmospheric/ocean conditions. Almost everything except bacteria died. One survivor, the only creature known to have survived all five mass extinctions: the waterbear. It's a microbe, with a formal name of Tardigrade, which looks like a cross between a dust mite and a blind bear. Forget the honeybadger, don't mess with the waterbear.
What're you lookin' at???
Also, during the segment, Tyson is standing in some kind of central hall with corridors leading off. One is called a "nameless corridor", and left explicitly for another show. The dinosaur extinction? The expected mass extinction due to modern, human-caused climate change? We'll have to see what Tyson has in store for us.
Tyson takes the connection between living things and their planet on a ride around the solar system, stopping on Titan, one of Saturn's moons. Titan has a lot of liquid methane and ethane, two chemical compounds that are almost always gas on Earth. Titan is cold enough that the gases have condensed to form rivers, lakes, and seas. There's no oxygen; the temperature is ridiculously lower. What kind of life would ever be able to exist there?
You gotta' like how farts smell to live on Titan
We don't know. Tyson's final segment is about what still needs to be discovered, mainly how life even arose in the first place. How did inorganic matter organize into the first protein codes for building life? We don't know. And that, Tyson tells us, is okay. It's okay to not know everything. As science is the frontier between the known and unknown, defining what we don't know and coming up with a plan to know it is how we make progress.
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