NARRATOR: Ok, go to the window. Or better yet, step outside. A squirrel darts past. Trees and weeds surge up towards the sky. Birds tickle the air. Get down on the ground and there’s more—worms wriggling, mushrooms sprouting, beetles crawling. There’s stuff you can’t even see, like bacteria. And everywhere you go on this planet – on land, underground, in the air, and in the water—there’s more life to be found.
And all of it—even you—is shaped by the most incredible of forces. Evolution.
DANIEL MATUTE: Evolution essentially multiplies majesty by majesty by majesty.
NARRATOR: And our understanding of all that majesty – it goes back to the mid-1800s, when an English 20-something, a guy named Charles Darwin, got an invitation he couldn’t refuse.
JANET BROWNE: To travel ’round the world. It was 5 years. And that voyage made him into a thinker.
JOEL CRACRAFT: He was just a great naturalist—he saw things out in nature, and he asked: “Why?”
NARRATOR: As in, why is there such a stunning diversity of life? Why are similar looking species sometimes located on opposite sides of the planet?
It was Darwin and Alfred Russel Wallace – who independently puzzled out a mechanism behind evolution.
JANET BROWNE: Which was natural selection.
NARRATOR: Natural selection just means that nature—the natural environment—is what’s selecting which organisms survive long enough to reproduce. And it depends on two key ingredients.
The first is some way of getting features, or traits, to be inherited from one generation to the next, which usually means reproduction.
The second is variation. If organisms were to make exact duplicates of themselves every time they reproduced, nothing would change. There’d be no elephants, no pine trees, no humans—we’d still just be single-celled proto-organisms.
Now, the environment can’t support every individual that’s born. Maybe it’s too dry or too wet for some of them, maybe all the food’s up in tall trees, maybe there’s not enough food, or maybe it’s just really cold. Whatever it is, organisms compete for resources. And this is where selection comes in.
For instance, scientists believe that a few hundred thousand years ago, before there were polar bears, some brown bears got stranded in the Arctic. The few that survived likely had fur coats that were a bit thicker, and lighter in color than the others. That would’ve kept them warmer, and helped them blend in with the snow to sneak up on prey more easily.
The point is—not all variations make it.
ASH BULLARD: And the things that survive go on to reproduce.
NARRATOR: In other words, survival of the fittest. Which doesn’t necessarily mean the biggest or the strongest.
SUSAN PERKINS: Fittest in an evolutionary sense is whoever has the most descendants.
NARRATOR: In the Arctic, the bears with thicker and whiter coats survived more often and had more offspring – offspring that inherited the thicker and whiter fur. And gradually, other changes accumulated too. Until this population became a separate species from the brown bears.
However, if we were to swap out the snow for a forest, having polar bear-like fur would likely be a bad thing.
In other words, evolution doesn’t progress in one fixed direction—but it’s not entirely random either. With so many environments selecting for all kinds of traits, evolution has resulted in the countless species that have lived on Earth.
Now, Darwin wrote these ideas down.
JANET BROWNE: He was not a visual man.
NARRATOR: So when he did bother to draw something, people took notice. Like this image he sketched in one of his notebooks.
JANET BROWNE: It’s a tree.
JOEL CRACRAFT: And it tells us how things are related. That is, they all can be traced back to a common ancestor.
NARRATOR: That ancestor—the first living organism on our planet—is at the base of the tree trunk. Here’s another view of this so-called phylogenetic tree. As life’s evolved over the last 3.8 billion years, new species have branched off, leading to entire lineages of different organisms.
SUSAN PERKINS: Every branching point in that tree is a story.
NARRATOR: Stories of global domination, of extinction. Stories of beauty, and of remarkable adaptation to an ever-changing world.
DANIEL MATUTE: I mean, the goal of the tree of life is: try to understand how every species is related to each other. The breadth of this – that is amazing.
NARRATOR: And that’s where you come in. In NOVA’s Evolution Lab, you’ll be climbing around the tree of life to build out portions of that tree. To see how evolution really works, and understand why it matters to you. Like: did you eat a dinosaur last night for dinner? Can you save someone from a venomous snakebite? Or do you have a Neanderthal ancestor?
Play this Lab, build the tree of life—which is your family tree, and discover just how connected you are to everything that’s alive and everything that’s ever lived.