Sep 20, 2018

Infective Heredity

Today, a fast moving, sidestepping, gene-swapping free-for-all that would’ve made Darwin’s head spin.

David Quammen tells us about a shocking way that life can evolve - infective heredity. To figure it all out we go back to the earliest versions of life, and we revisit an earlier version of Radiolab. After reckoning with a scientific icon, we find ourselves in a tangle of genes that sheds new light on peppered moths, drug-resistant bugs, and a key moment in the evolution of life when mammals went a little viral.

Check out David Quammen's book The Tangled Tree: A Radical New History of Life 

This episode was produced by Soren Wheeler. 

Support Radiolab today at Radiolab.org/donate

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Jad Abumrad:

Oh wait, wait, you're listening to-

 

Speaker 2:

Okay.

 

Jad Abumrad:

All right.

 

Speaker 2:

Okay.

 

Jad Abumrad:

Alright.

 

Speaker 2:

You're

 

Jad Abumrad:

listening

 

Speaker 2:

to radiolab.

 

Speaker 3:

Radiolab.

 

Speaker 2:

Radiolab

 

Speaker 3:

From

 

Speaker 2:

WNY

 

Speaker 3:

C?

 

Speaker 2:

C

 

Speaker 4:

That incredibly talented young boy was soon a talented young man composing symphonies, con [crosstalk 00:00:24]

 

David Quammen:

Hello, hello.

 

Robert Krulwich:

Hello

 

David Quammen:

Robert, hi

 

Robert Krulwich:

Hi, let me just[crosstalk 00:00:28]

 

Jad Abumrad:

Wow, what was that?

 

Robert Krulwich:

That wa- that was the, um, mist of classical music that is public radio being suddenly interrupted by science journalist and author David Quammen.

 

David Quammen:

Hey, are we all here now?

 

Robert Krulwich:

Now we're all here.

 

Robert Krulwich:

And you are Jas Abu mrad

 

Jad Abumrad:

Yes I am

 

Robert Krulwich:

I am Robert Kruller, this is Radiolab.

 

David Quammen:

Yeah yeah.

 

Robert Krulwich:

And actually what happened here is I, I called David because he has just published a book, which contains an idea that I found so surprising, I, I had not, known of this. It's kind of a, a smack in the face to Charles Darwin's theory of evolution.

 

David Quammen:

Yes. There have been a number of ????? that have been added to Darwin's theory over the 150 years or so since he published it, but this is, this is more than that, this is a big fricking asterisk.

 

Robert Krulwich:

(Laughs)

 

Robert Krulwich:

And to explain what that means, David told me a story about a moth.

 

David Quammen:

Yes, uh, the peppered moth. It lives in forests of central England among other places and during the 19th century, this moth was white with little flecks of black on it, and um, these moths sometimes roost on the, on the trunks of trees, and the trunks of trees surrounding Manchester, England, were kind of light colored. So when these moths roosted on the trees they were pretty well camouflaged, a light, slightly peppered moth on a light, slightly peppered tree trunk. So they were protected against predation by birds. And then the tree trunks changed. Why did the tree trunks change? Because of the industrial revolution, because of smoke stacks of Manchester were turning out a lot of coal smoke, they were burying coal for all their industrial processes. And there was this soot, this coal soot that was coming out, and it was blanketing the trees in the nearby forest, so the tree trunks turned black. And the moths were no longer camouflaged. 'Cause the moths were white.

 

Robert Krulwich:

You wouldn't wanna be a white moth sitting against a coal black tree because then you're, you're [crosstalk 00:02:35]

 

David Quammen:

No, no.

 

Robert Krulwich:

bird would know exactly where you are.

 

David Quammen:

Right. What happened? The moths turned black.

 

Jad Abumrad:

Oh yeah sure, this is the, this is the classic sort of evolution story.

 

Robert Krulwich:

Exactly. That story was told, it was, it because a textbook example of Darwinian evolutionary change in, in real time, and the way that happens were we're told, is that once the trees turned dark the moths-

 

David Quammen:

Changed by incremental mutation.

 

Robert Krulwich:

Like, you know, thanks to some tiny little mistake in some moth gene-

 

David Quammen:

The- the black speckling got bigger on certain moths, and those were a little bit more protected, and then the speckling got a little bit bigger, the moths got a little grayer [crosstalk 00:03:18]

 

Robert Krulwich:

And then very, very slowly over generation after generation after generation of moths, they get a little bit darker, and then darker still, 'til you end up eventually with a population of moth that turns completely black.

 

David Quammen:

That's the classic story.

 

Robert Krulwich:

Except-

 

David Quammen:

Except that we now know that's wrong.

 

Robert Krulwich:

It turns out it wasn't slow. It didn't take generations and generations.

 

David Quammen:

Sequencing of the moth genome has revealed a stretch of DNA, 22,000 letters of the DNA code, that suddenly jumped into these moths from somewhere, and in a flash the moths changed from white to black.

 

Robert Krulwich:

Pretty much in one day, really, a white peppered moth mom all of a sudden produces an all black baby.

 

Jad Abumrad:

Wait so how did that, how did that happen, they said a whole packet of genes just got shoved into this new, from, where did it comes from?

 

Robert Krulwich:

Well, David says it probably jumped from one part of the moth genome to a completely new part, different part. But what that means, of course, is that living things, it turns out, can change way faster than we thought, and therefore evolution can happen much faster than we thought. And on top of that, David says, scientists have now discovered this even stranger kind of super fast change that takes things that we- about parents and offspring individual species, things we've counted on for years, and just throws the whole mix into the air.

 

David Quammen:

Yes. Infected heredity.

 

Jad Abumrad:

Infective heredity. What is, what is that?

 

Robert Krulwich:

Oddly enough to explain this to you i have to go back-

 

Jad Abumrad:

Hello I'm Jas Abu mrad.

 

Robert Krulwich:

And I'm Robert Kruller.

 

Jad Abumrad:

And this is radiolab [crosstalk 00:05:03]

 

Robert Krulwich:

To an earlier version of us because it was 11 years ago I think that we made a show called, uh, "(So-Called) Life".

 

Jad Abumrad:

Life, not as we know it.

 

Jad Abumrad:

Oh, God, that show

 

Robert Krulwich:

And in that show we dealt with an early sort of more primitive version of this very question. So I'm jut gonna play you a few minutes of that, of that earlier show.

 

Robert Krulwich:

Let's talk about life, you and I [crosstalk 00:05:23]

 

Robert Krulwich:

And we'll come right back.

 

Robert Krulwich:

[crosstalk 00:05:24] when you look around at the world at living things and I say look, cat, there's a cat, and next to that is a dog, and that's a tree, and you notice that those things, of course, are different.

 

Jad Abumrad:

Yes

 

Robert Krulwich:

And then later when we go to school we learn about phylums and categories like kingdoms and stuff, so we learn about the nature of those differences and then you're taught about struggle, and competition-

 

Jad Abumrad:

Darwin, survival, and fitness [crosstalk 00:05:45]

 

Robert Krulwich:

Darwin, and species, and all that. There is a new theory that's being talked about that turns all of that on its head. I heard it first from this guy.

 

Steve Strogatz:

Um, I'm Steve Astrogate. I'm an applied mathematician at Cornell and [crosstalk 00:05:58]

 

Robert Krulwich:

And story he told me, which is based on analysis of DNA in very tiny organisms-

 

Steve Strogatz:

Microbes.

 

Robert Krulwich:

Is that once upon a time, he says, life began with a very primitive, very simple collection of cells and these cells, said Steve-

 

Office:

(Singing)

 

Jad Abumrad:

(Laughing)

 

Robert Krulwich:

These cells like to share.

 

Steve Strogatz:

It appears that as you, when you go back far enough, there's a kind of rampant sharing of molecules. It's a kind of orgy in which there are no well defined species or organisms, and I can give you my genes and you can pass- we're a, we're a commune.

 

Office:

(Singing)

 

Office:

(Laughing)

 

Jad Abumrad:

I totally remember recording that.

 

Soren Wheeler:

The kumbaya singing?

 

Robert Krulwich:

That's Siren Wheeler who was there at the start. He produced this piece years ago.

 

Jad Abumrad:

Yes.

 

Soren Wheeler:

I think it was just us around the office humming.

 

Jad Abumrad:

Yeah

 

Office:

(Singing)

 

Office:

(Laughing)

 

Robert Krulwich:

It was a commune.

 

Jad Abumrad:

What does, what does that mean i-it was a commune?

 

Robert Krulwich:

What do you mean, what does it mean. It means [crosstalk 00:06:45]

 

Jad Abumrad:

Well I, I mean, I know what it means in the '60s free love sense, but what does it really mean?

 

Robert Krulwich:

What are- what cells are exchanging is chemicals. Chemicals that give them talents and traits, genes. Here's what happens, I did this with Steve. In our ancient puddle, I mean, Darwin thought that life might have begun in a warm puddle.

 

Jad Abumrad:

Mm-hmm (affirmative)

 

Robert Krulwich:

lets say that you and I are both cells.

 

Steve Strogatz:

Okay

 

Robert Krulwich:

So once upon a time there was you in a puddle and I'm in the same puddle as you.

 

Steve Strogatz:

Mm-hmm (affirmative)

 

Robert Krulwich:

And it, it gets a little colder in the puddle so we should all get sick, but you don't get sick. You have some kind of accidental talent, you can handle cold water. I'm shivering describe again what happens at this point?

 

Steve Strogatz:

(Laughs)

 

Robert Krulwich:

In the glorious old days.

 

Steve Strogatz:

Well, my membrane, that is I-I'm a cell, I've got a membrane, I've got my outer layer, may be a little bit porous, and maybe- whoops- some of my genes just leaked out

 

Robert Krulwich:

(Laughter)

 

Steve Strogatz:

Okay, we're not talking sophisticated organisms.

 

Robert Krulwich:

Right

 

Steve Strogatz:

And maybe you're porous too, and, oh wow, you've just absorbed some of those genes.

 

Robert Krulwich:

So now we both have this.

 

Steve Strogatz:

We both got it.

 

Robert Krulwich:

We both got it. And if I've got this gene now, I can survive cold water because it's part of me, and if I bump into you - now it's part of you. So now the Steve gene has become a Robert gene, which has them become a Jas gene, and we're doing this over and over and over, and we're getting really, um, communal.

 

Office:

(Singing)

 

Jad Abumrad:

It sounds so friendly.

 

Steve Strogatz:

No, no, a-actually it, it-

 

Robert Krulwich:

Don't think of cells like people.

 

Robert Krulwich:

Shut Up.

 

Robert Krulwich:

All these exchanges, this gene swapping, was not intentional.

 

Nigel Goldenfel:

It's not purposeful sharing.

 

Robert Krulwich:

That's Nigel Goldeneye.

 

Nigel Goldenfel:

I'm a theoretical physicist at the University of Illinois.

 

Robert Krulwich:

And he and his colleague Carl Worse, did the science that led to some of these kinda goofy ideas.

 

Nigel Goldenfel:

It's not me sort of saying "Hey I'm gonna just help out my buddy over there, here's a couple of genes I think you'll find handy." It's not something like that.

 

Jad Abumrad:

Even still, if we're swapping genes so much, and you know, you're giving me yours and I'm giving you mine,

 

Robert Krulwich:

Yeah.

 

Jad Abumrad:

What does it actually mean to be, me?

 

Robert Krulwich:

Yeah.

 

Jad Abumrad:

If so much of me is spread around.

 

Robert Krulwich:

Well, it would be very weird. Imagine a world in which, for a while, I have your nose. God forbid.

 

Robert Krulwich:

(Laughing)

 

Jad Abumrad:

(Laughing)

 

Robert Krulwich:

And then I get my nose back, you have Steve's hair, then uh, Steve would get my ear, then he would get your nose.

 

Steve Strogatz:

Once you start having a lot of exchange-

 

Jad Abumrad:

I'll take your chin.

 

Robert Krulwich:

Okay, you can have my, um, allergies.

 

Nigel Goldenfel:

Then you start even asking what does it mean, um, to be a species.

 

Jad Abumrad:

You can have my, um, love affair with doubt.

 

Robert Krulwich:

(Laughs)

 

Nigel Goldenfel:

Uh, you may not even be able to talk about individuals

 

Robert Krulwich:

Yeah. If the mixing is good enough we're all kind of indistinguishable, so identity would be very strange in this ancient world.

 

Steve Strogatz:

A lot of the concepts that we take for granted in, in biology become more and more nebulous as you get further and further back to the root of the origin of life.

 

Robert Krulwich:

Take, for instance, Charles Darwin. What Nigel's really saying is for the first billion years of life-

 

Jad Abumrad:

With a "b".

 

Robert Krulwich:

With a "b". Everything that Darwin teaches, all that stuff hasn't happened, there's no borders, no individuals, there's no species.

 

Steve Strogatz:

That is, Darwinism, evolution as we now understand it, that's an interlude. In the real story of life. It's only what's happening now.

 

Robert Krulwich:

What you got back at the very beginning was a whole bunch of cells swapping genes, swapping advantages, swapping disadvantages. It's kind of a wild time.

 

Steve Strogatz:

A tremendous explosion of diversity in a way that life has not seen since then.

 

Robert Krulwich:

Until...

 

Robert Krulwich:

One dark and terrible day-

 

Jad Abumrad:

(Laughs)

 

Robert Krulwich:

-three billion years ago, as interpreted by Freeman Dyson, famous physicist.

 

Jad Abumrad:

Freeman Dyson.

 

Robert Krulwich:

And delivered here now by our friend the mathematician Steve Astrogate. Here's Steve.

 

Steve Strogatz:

One evil day, a bacterium anticipating Bill Gates by three billion years, refused to share.

 

Steve Strogatz:

Refused to share.

 

Robert Krulwich:

Ooh.

 

Steve Strogatz:

The first bad guy is this cellular Bill Gates who- who decides that I've- I've got an innovation that I don't feel like sharing, or possibly if I've found a way to keep my membrane from leaking. That is, I'm not going to be a sharing soul any more.

 

Jad Abumrad:

And why? I mean, what made that one little cell decide to stop sharing?

 

Steve Strogatz:

That's a good question. WE don't really know.

 

Robert Krulwich:

But what we do know.

 

Steve Strogatz:

This is, was maybe the most dramatic moment in the history of life on earth.

 

Steve Strogatz:

This transition from the age of, if you want to call it, the age of sharing, to the age of selfishness.

 

Robert Krulwich:

And gradually, once one creature stopped sharing, pretty soon the others followed, and then more and more did the same thing and now, for the first time in the history of life, finally we get Darwin. No we get get species. Now we see differences.

 

Steve Strogatz:

Yes it's the age of identity, of individualism. It's also the age of, of stasis.

 

Robert Krulwich:

Things change but they change much more slowly.

 

Steve Strogatz:

And any great thing, you know, like you are a bat and you figured out sonar. I, I don't have sonar. I can't get sonar.

 

Robert Krulwich:

(Laughs)

 

Steve Strogatz:

It'd be nice to have sonar. Or you're like you a little electric fish that lives in the muddy water of the Amazon. You don't care its totally dark, you can see because you can see with electricity. I can't see with electricity. If I'm in the dark I'm bumping my head.

 

Jad Abumrad:

Did we really use Bill Gates as a stand in for, like, selfishness??

 

Soren Wheeler:

Yeah, well, I mean, at the time he was the ultimate corporate-

 

Jad Abumrad:

That's ho-

 

Jad Abumrad:

Oh that's horrible that we did that. [crosstalk 00:12:12]

 

Soren Wheeler:

[crosstalk 00:12:13] Gates Foundation.

 

Soren Wheeler:

(Laughs)

 

Robert Krulwich:

That's right he's actually gone over to the light side instead of the dark side.

 

Steve Strogatz:

Yeah right. Exactly.

 

Soren Wheeler:

That is, uh, Steve Astrogate. I ended up calling him up just to chat him through some of this stuff and he told me that he actually heard this whole idea from a lecture by physicist Freeman Dyson.

 

Steve Strogatz:

Dyson is just a great writer and a great speaker and he had this memorable line in there, at least memorable to me, when he started talking about, I mean he phrased the whole thing in terms of sharing, which may be why in that previous episode we had that kumbaya singing.

 

Steve Strogatz:

(Laughter)

 

Soren Wheeler:

That wasn't my doing by the way.

 

Steve Strogatz:

No, no, that was, that was us.

 

Steve Strogatz:

But anyway, so, then he said, one evil day some privative bacterium anticipating Bill Gates by 3 billion years refused to share its DNA.

 

Soren Wheeler:

Oh so that was

 

Robert Krulwich:

That was Freeman Dyson's-

 

Steve Strogatz:

That's his, yeah that was his joke.

 

Steve Strogatz:

So anyway I was sitting there in this lecture and he started mentioning a certain biologist, Carl Worse. And he talked about him in such glowing terms as one of the great microbiologists of our time. And um,

 

Jad Abumrad:

So you- so you hadn't heard of Carl Worse before that?

 

Steve Strogatz:

No I had not.

 

Jad Abumrad:

So I, the reason I was asking is that-

 

Robert Krulwich:

I think in the show we actually mentioned Carl as, as I remember it.

 

Soren Wheeler:

You know I don't know if you guys know this or not but that was 11 years ago, right, I was actually an intern at the time. I'd just showed up and I was tasked with tracking down Carl Worse, who's the guy who we mentioned as sort of like, the grandfather of this idea and he was like, a huge, huge deal in science um he discovered this whole other branch on the tree of life, the archaea

 

Jad Abumrad:

Oh he's Mr. Archaea?

 

Robert Krulwich:

It's pretty big one, its a whole, a whole nother kingdom of life.

 

Soren Wheeler:

Yeah. It got him on the front page of the New York times and I, I had to track him down and it turns out he was like, the just most classic, curmudgeonly scientist.

 

Soren Wheeler:

(Laughter)

 

Soren Wheeler:

It took me 20 emails to get him to even, like, just let us talk to his collaborator Nigel Goldeneye who we talked to in the show, but whatever, he was a very strange, he was a very curmudgeonly man. But you know, like he came to like me and I actually spent some time with him in his office and we, I can do the curmudgeonly thing if I need to, you know, we-

 

Soren Wheeler:

(Laughter)

 

Jad Abumrad:

You've got those skills.

 

Soren Wheeler:

Yeah, I could, we passed some curmudgeonly jokes back and forth, and, uh anyway, uh, after he heard the piece he wrote me the most seething, scathing email.

 

Jad Abumrad:

Oh no

 

Soren Wheeler:

About- And nothing, there was nothing in it about like, you got this wrong. It was just, like, you made a cartoon of my work. Which honestly, now, listening back I agree with him a little more than I did at the time.

 

Jad Abumrad:

Yeah, yeah.

 

Soren Wheeler:

But he was like "I'm a serious person and you've made this into, like. a dog and pony show." And I was like, I was brand new.

 

Jad Abumrad:

Yeah.

 

Soren Wheeler:

And it hurt, I mean like, I was, I felt like really, really bad. And he's like, you've disrespected Nigel, and so I wrote, I wrote, I called up Steve maybe and said "Oh man, you know this happened." And Steve was like, hey listen, forget them.

 

Soren Wheeler:

(Laughter)

 

Soren Wheeler:

Don't worry about it.

 

Jad Abumrad:

I love Steve.

 

Steve Strogatz:

Yeah, I don't know, I, I, it sounds like something I might have said.

 

Soren Wheeler:

Do you remember having that conversation?

 

Steve Strogatz:

I honestly don't remember having that conversation.

 

Soren Wheeler:

And then I was like, I needed that so bad at the moment in my career, for someone like, with Steve's stature to like, balance it out in that way.

 

Jad Abumrad:

Yeah.

 

Steve Strogatz:

Um, yeah, I think, I mean it's a little bit funny that he would, to me, a little surprising, that he wouldn't have gotten what you were trying to do-

 

Soren Wheeler:

Yeah.

 

Steve Strogatz:

-or what we were trying to do. I think our playfulness, in an attempt to be clear, and to communicate, and to attract people who may not otherwise not listen to a story about something called horizontal gene transfer. He should've gotten that, because he himself in his writing was very playful.

 

Soren Wheeler:

Mm-hmm (affirmative)

 

Steve Strogatz:

He was very fun to talk to, I mean he was absolutely, Carl was very playful and harrassable and grouchy and charming-

 

Soren Wheeler:

Yeah

 

Steve Strogatz:

-but he would certain tell you what he thought.

 

David Quammen:

Yeah, yeah, this guy is a great character.

 

Jad Abumrad:

And David it turns out in his new book talks a lot, a lot a lot about Carl Worse and this revolution in our thinking about the evolution of life.

 

David Quammen:

Towards the end of his life he started to think he was more important and, um, more profound than Darwin. He got a very negative attitude, toward, towards Charles Darwin.

 

Robert Krulwich:

And on Darwin's birthday he said he send, he sent out a note that everybody should, that this should be a day of rage

 

David Quammen:

That's right. Yes, he did that.

 

Robert Krulwich:

but what I'm wondering is, now that you've spent a book's attention on him, do you feel that he has some right to say that the picture we have of how life changes needs serious amending or is he just barking because he's a barker?

 

David Quammen:

No, he, um, he was entitled, not to think that he was greater than Darwin, but to think that what he discovered was very, very damn important to understanding the full history of evolution on earth. What has happened all throughout the history life on the planet for a billion years and is still happening today. This is where we are now.

 

Robert Krulwich:

The crazy details coming up right after the break.

 

Speaker 12:

This is Yong Yun calling from Astoria, New York. Radiolab is supported in part by the Alfred P. Sloan Foundation: enhancing public understanding of science and technology in the modern world. More information about Sloan at www.slone.org.

 

Speaker 13:

Great podcasts deserve a great platform. That's why Pocket Casts delivers a beautifully designed, simple but powerful experience that offers more control. It's the premium app for podcast listening, search and discovery. And it's now free. Download Pocket Casts at pocketcasts.com or find us in the Apple App or Google Play stores.

 

Jad Abumrad:

Jas.

 

Robert Krulwich:

Robert.

 

Jad Abumrad:

Radiolab

 

Robert Krulwich:

And we're back with David Quamman, and this new, new to us, way of changing life.

 

David Quammen:

Infective heredity. These leaping genes, these transfers of DNA that create new genetic possibilities, in a blink.

 

Robert Krulwich:

Turns out, David told us, that the swapping of genes that we talked about in the early history of life, that's still happening today.

 

David Quammen:

Correct. Yes.

 

Robert Krulwich:

Bacteria all around us.

 

David Quammen:

Those bugs are trading genes. Genes are jumping sideways from one kind of bacterium to another. Even in our bellies, even in our guts.

 

Robert Krulwich:

So let's say that you go to France on a vacation and you touch something there. And then you lick your finger. I don't know why, or, or you eat something. Now new bacteria from that European food is going into you stomach, and now not only do you have some new bugs in you, but they can start trading their genes with bugs that are already in you.

 

David Quammen:

Yes

 

Jad Abumrad:

What would that mean, like, physically, like would it look like, out the cell wall and then...?

 

David Quammen:

Well, they've found that there are several different mechanisms for this. Two bacteria would create a little pipe, a little sort of penis like thing, between them and genes would be transferred. But genes were moving sideways under other circumstances too. From dead, busted open bacteria into live bacteria-

 

Robert Krulwich:

Has it acquired this new trait at once?

 

David Quammen:

Immediately.

 

Robert Krulwich:

Immediately.

 

David Quammen:

So in an instant, a new population, even a new species of bacteria can possess all of those gradually, laboriously acquired adaptations that, um another strain of bacteria evolved.

 

Robert Krulwich:

These bugs, they don't have to wait around for generation after generation to pick up random mutations. Our bacteria inside us can pick up whole new abilities and new tricks all at once from their new neighbors.

 

David Quammen:

So for instance, one kind of bacteria could pass genes for antibiotic resistance to another completely different kind of bacteria.

 

Robert Krulwich:

So say you've got somebody sitting in a hospital with a, uh, staphylococcus infection. Some of the bugs inside her figured out how to resist penicillin.

 

David Quammen:

When that bug then comes out of that human and it gets left on a table in a hospital and someone else gets infected by it, then they will also have an infection that is resistant to penicillin.

 

Robert Krulwich:

But if say, they happen to be in the hospital sick with something totally different, they have a different kind of harmful bacteria doing trouble, giving them trouble, then those old bacteria in them can learn, in a flash, from the new bacteria. Now everybody's penicillin resistant.

 

David Quammen:

And that's why, th-that's why antibiotic resistance is spreading around the world so lickety-split. That is really important, that's a, that's a global health crisis, and the World Health Organization, among others, have called that a global health crisis. Tens and tens and tens of thousands of people are dying from that so that's really important and urgent. But the most important part of this whole subject is not practical, it's a matter of understanding, understanding the history of life, understanding who we are

 

Robert Krulwich:

Quite literally because according to David the way we are, we humans are, has been affectd by visits from other creatures' genes.

 

David Quammen:

Yes 8% of the human genome is viral DNA.

 

Robert Krulwich:

8% of the human-

 

David Quammen:

That DNA has come into humans, or into our mammal ancestors, sideways.

 

Robert Krulwich:

So here's how that goes. Like, you're siting around, and a virus gets into your blood stream, and it travels into one of your cells. And when it's in there it drops some of its DNA into your DNA, and if it gets into an ovary cell or a sperm, well then it will be passed along.

 

David Quammen:

So 8, 8% of our genome has come to us that way, from these viruses. Some of that is just gobbledygook in our genome, and some of it is instructions, in other words genes, that are still performing functions. And one of those creates a boundary layer between the human placenta and the fetus, an absolutely necessary essential boundary layer.

 

Robert Krulwich:

Now this is, came as a total shock to me because, after all, the thing that's really special about mammals is that-

 

David Quammen:

Female mammals, uh, or at least placental mammals, um, carry young around inside the body [crosstalk 00:22:47]

 

Robert Krulwich:

In the history of life this was a completely new development. I mean you, you think about fish, you think about reptiles, like, the dinosaurs, you think about the birds. What do they do when they have kids? They lay eggs. But now we get a creature that comes along and figures out how to keep the baby growing inside it. Of course if it does that it has to make sure it, its immune system doesn't attack that baby, and the baby has to be able to poop and stuff like that and get things out so there has to be some kind of boundary.

 

David Quammen:

And how did we get that good idea? We got that good idea from a virus.

 

Robert Krulwich:

Long, long ago some ancient mammal ancestor got a virus, got infected by a virus, and that virus introduced a new gene.

 

David Quammen:

In the original virus it created an envelope, a wrapping, around the virus, but it is been adapted to create a different kind of wrapping, the wrapping that goes around the fetus, and inside the placenta so it carries nutrients in, it protects the fetus from the mother's immune system, and it is allowing waste products from the fetus to be carried away and disposed of by the mother.

 

Jad Abumrad:

I mean, is this potentially the origin of mammals and would this being the without which if we hadn't gotten this talent from viruses we wouldn't have gotten the kinds of mammals that we have now?

 

David Quammen:

That, that layer could not exist and does not function without this viral gene telling it what to do.

 

Robert Krulwich:

Without this little bit of, of virus DNA-

 

David Quammen:

You can't be a mammal. You can't be a m-mother mammal and you can't be a child.

 

David Quammen:

In light of this stuff and, and for me in light of five years of studying it and, and following it and interviewing people about it, the categories that we apply to the world, categories like "individual", and "species" now appear more blurry. The edges are fuzzy. Is there such a thing as a human individual? Or is a human a composite of other forms of life, and what does that says is that we are composites, we are mosaics. It's, it's humbling and it's, and it's fascinating to think of yourself that way. Like for me, David. So it turns out that David is not just the descendent of a Norwegian father and a German-Irish mother, but he's also viral, and bacterial, and who knows what else. and I find that, um, I find that thrilling. Uh, I'm, I'm grateful to all those other limbs on the tree of life for the things that they've given us.

 

Robert Krulwich:

Thanks of course to Steven Astrogate of Cornell University, um, who is always willing to jump back into the pond, which he long since had left and thought he'd got dried off from. David Quamman's new book is called "The tangled Tree", and it's a gorgeous book. So thanks to them.

 

Jad Abumrad:

And thanks to all of you for listening. I'm Jas Abu mrad

 

Robert Krulwich:

I'm Robert Kruller

 

Jad Abumrad:

We'll see you next time.

 

Office:

(Singing)

 

Jad Abumrad:

Wait a second. Is that Kumbaya?

 

Robert Krulwich:

Well- that's a sly ruse [inaudible 00:26:45] Kumbaya.

 

Jad Abumrad:

You snuck it in, you Trojan horsed it.

 

Robert Krulwich:

(Laughing)

 

Speaker 14:

My name is [inaudible 00:26:51] calling from Mexico City. Radiolab was created by Jas Abu mrad and is produced Siren Wheeler. Dylan Keefe is our director of sound design. Maria Matasar-Padilla is our managing director. Our staff includes Simon Adler, Becca Bressler, Rachael Cusick, David Gebel, Bethel Habte, Tracie Hunte, Matt Kielty, Robert Kruller, Annie McEwen, Latif Nasser, Malissa O'Donnell, Arianne Wack, Pat Walters, and Molly Webster. With help from Shima Oliaee. Our fact-checker is Michelle Harris.

 

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