Name: What Was the Ancestor of Everything? (feat. PBS Space Time and It’s Okay To Be Smart)
Uploaded: 2021-05-03T00:31:37.000Z
Duration: 11 min 44 s
Description: VoiceTubeの動画で発音を聞きながら英語表現を覚えよう！学べる英語：

Part of what draws us to the study of natural history is our desire -- our drive -- to understand

The more fossils that we can find and study, the more branches and twigs we can add to

the tree of life -- that web of relationships that connects all organisms, living and extinct.

As any astrophysicist will tell you, the story goes back way farther than any fossil.

The story of life actually begins with, well, the beginning of everything.

In the aftermath of the Big Bang the universe was an energetic, structureless mess.

But that mess pulled itself together into atoms and stars and galaxies and planets and,

How did these little eddies of order form in a universe otherwise prone to increasing

I'm Matt O'Dowd from PBS Space Time, and you can learn all about the physics of the

origin of life in a video over on our channel

But for us here on Eons, the search for our origins go back to a single common ancestor

If you trace all of the branches on the tree of life backward, you realize they all come

That initial point, before anything branches, is a single species.

Darwin himself theorized that such a thing once lived.

He called it a “primordial form into which life was first breathed.”

Today, scientists call it the last universal common ancestor, or LUCA.

LUCA isn't the first thing to have lived.

Instead, it's the common ancestor of everything that's alive today.

Today, Eons is teaming up with our friends at Space Time and It's Okay to Be Smart

Even though Darwin suggested that there was a universal common ancestor, we couldn't

even guess what it might have been -- until we started to master genomics, the science

of mapping and studying the genetics of all living things.

Today we know that all life uses the same molecules of RNA, DNA, and protein.

And the genetic code that's responsible for making that stuff is basically universal,

That's one of the best arguments to support the notion that everything came from the same

It's also why most of the research that's gone into learning what LUCA was has involved

comparing the genomes of all kinds of living things, to see what else they have in common.

One of the first to take this approach was American biologist Carl Woese

In 1977, he discovered the existence of organisms that would make up a whole new domain of life,

They're a group of prokaryotes -- simple, single-celled organisms that are vaguely similar

But they turned out to be so diverse, and so different from any other living thing,

that Woese proposed a new tree of life -- one that divided life into three domains: archaea,

And, he said, where those three main branches converged, there was LUCA.

But he saw the three domains arising not from a single cell, but from a chaotic environment,

more than 4 billion years ago, when cells didn't quite exist yet.

In this scenario, he proposed, there were extremely simple things that were even more

He called them progenotes and envisioned them as tiny scraps of genetic information, surrounded

These progenotes wouldn't have been complex enough to create true offspring.

They might have been able to copy their genetic material, but not accurately.

So instead, they may have just floated about at random, constantly swapping little snippets

Sometimes, that genetic info might have worked well for a progenote, and could be copied.

But out of this basically random transfer of information, Woese thought, some of the

For instance, the genetic code that makes up genes as we know them could have come about

But that information might have been stored in RNA, not DNA as it is today.

To explain how that might have worked, here's a biologist I know who specializes in RNA:

Dr. Joe Hanson, host of It's Okay to Be Smart:

Now, RNA, in addition to storing information, can do stuff – biochemical reactions – like

we see in the ribosome, where RNA is used to not only code for, but also build, proteins.

Early on, RNA machines like the ribosome would have evolved alongside genetics version 0.1.

So, it's likely first life arose and evolved in this so-called RNA world, and only began

storing genetic information in DNA later on.

For more on how this happened -- and other theories about how life first arose on Earth -- check

out our video over on It's Okay to Be Smart.

So, instead of being a specific organism, or even a group of things.

Woese thought that LUCA was the whole process by which progenotes acquired the genes to

And from them would have come three lineages that evolved into modern bacteria, archaea,

Now, Woese's view of LUCA hasn't been abandoned, but many scientists have moved

That's partly because, when Woese was publishing these ideas, genetic sequencing was just coming

Back then, only a handful of genomes had been sequenced.

And now we've mapped the genes of thousands of living things.

And that means we can try looking for LUCA in new ways -- like, by lining up genomes

from across all of the domains of life and comparing them to see what they have in common.

If a gene appears in basically every living thing -- so it's considered universal -- then

it must have come from LUCA ... or so the thinking goes.

So, many researchers who study LUCA are trying to reconstruct its genome.

One way to do that is by finding what they call the minimal genome -- the smallest amount

of genes that a cell can have and still survive.

Since these most basic, essential genes are thought to have come from LUCA, if we could

identify them, that could tell us how LUCA looked and lived.

This work has been spearheaded mainly by researchers in Maryland who have studied the genomes of

bacteria like Haemophilus and Mycoplasma.

And based on what those organisms had in common, the team proposed back in 2003 that LUCA probably