Imagine the tree of life. The tip of every branch represents one species, and if you follow any two branches back through time, you'll hit an intersection. If you keep going back in time, you'll eventually find the common ancestor for all of life. That ancestor is called LUCA, the last universal common ancestor, and there is no fossil record to tell us what it looked like. Luckily, we have Jonathan Lambert. He's a science correspondent for NPR and today he's talking all things LUCA: What we think this single-celled organism may have looked like, when it lived and why a recent study suggests it could be older and more complex than scientists thought. Have other questions about ancient biology? Email us at [email protected] — we'd love to hear from you!Listen to every episode of Short Wave sponsor-free and support our work at NPR by signing up for Short Wave+ at plus.npr.org/shortwave.In a previous version of this episode, we said that the research team used carbon-dated fossils to calibrate a molecular clock aimed at estimating the age of LUCA. In fact, the researchers used radio isotopic-dated fossils for that purpose.Learn more about sponsor message choices: podcastchoices.com/adchoicesNPR Privacy Policy
Chapter 1: What is LUCA and why is it important?
Chapter 2: What does LUCA tell us about the tree of life?
And if you follow any two branches back in time, they converge on their most recent common ancestor. So like chimps and humans, for instance, converge on a common ancestor that lived like less than 10 million years ago.
If you keep tracing any path of ancestry back far enough, whether you start with gorillas or sharks or ginkgo trees or those neat bacteria that live in the bowels of the earth, you'll eventually reach the same single point. That's Luca. That's the ancestor of every living thing and every dead thing that we know about.
Grandma. Wow. That's awesome. Why do we want to know about Luca?
Scientists want to understand what it was like because it gets at this really fundamental question of where we, as in all life on Earth, came from. And here's a new development. A team of scientists took the biggest swing yet at trying to paint a picture of Luca through some pretty tricky detective work.
So today on the show, how scientists use clues from life today to uncover what our last universal common ancestor may have looked like.
how it could be a bit older and more complicated than we thought, and if true, could hint that we're not the only life in the universe.
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Chapter 3: How do scientists study LUCA?
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All right, let's back up a second, John. How do we even know that Luca, who I fully believe in, but still, how do we know that Luca existed?
Evidence that it existed is hidden in every living thing. So we all share some basic fundamental machinery of life, things like a genetic code or using amino acids to build proteins.
I thought it was the desire to belong and, you know, have friends. Not that.
Yeah, yeah, not that. And given what we know about how evolution works, that genes get passed down from generation to generation, it follows that something like LUCA must have existed.
Right. If we share genes with bacteria, we must have gotten that from a shared ancestor way back when. So is look at just another term for the origin of life?
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Chapter 4: What challenges do researchers face in identifying LUCA?
In a way, you can think of it as almost the end of the story. of the origin of life as we know it, because all of the things that are in common across all of life that exists today would also have been already present by Luca.
Wow.
Yeah, and understanding the nature of the end of that story can still tell researchers a lot about early evolution.
Let's pick up that story then. How are researchers trying to tell it and figure out what Luca may have looked like?
So in general, all these efforts try to guess the genes and proteins that Luca had by looking for what's shared across different organisms. Like, for example, if you compare a gene that's basically the same in us and chimps, it's pretty safe to say that we inherited it from our common ancestor. That's the simplest explanation.
But that kind of inference gets a lot more complicated the further back in time you go.
What do you mean?
Well, genes get up to a lot of shenanigans that can throw off that detective work.
Well, what kinds of things can genes do to throw the scientist detective off their scent?
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Chapter 5: What new insights have emerged about LUCA?
Chapter 6: How do horizontal gene transfers complicate our understanding of LUCA?
What do you mean?
Well, genes get up to a lot of shenanigans that can throw off that detective work.
Well, what kinds of things can genes do to throw the scientist detective off their scent?
Yeah, so there's horizontal gene transfer, which is this thing where instead of passing genes vertically from one generation to the next, some microbes can pass them horizontally to their neighbors. Like a bacterium can give its other bacteria friends antibiotic resistance, for example, when it butts up against them and shares that little bit of DNA.
Oh, okay.
And so that can make it seem like a bunch of species all inherited this gene from a common ancestor when in reality it just got shared a bunch.
So that muddies the waters of the quest to draw a clearer picture of LUCA. What else does that?
Yeah. And then there's the issue of genes getting lost, but only for some species. Like if genes that were in LUCA get lost down the line in certain species, it could lead researchers to falsely conclude that the genes evolved after LUCA since it's not shared by all its descendants. Right.
I know enough about science as a non-scientist to know that this essentially means the data is really cluttered. Or like scientists would say, the data is really noisy.
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