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  • NATURE PODCAST

Podcast: Bird beak evolution, getting to Proxima b, and have physicists made metallic hydrogen?

Bird beaks show how evolution shifts gear, getting to Proxima b, and have physicists made metallic hydrogen?

In this episode:

00:41 Time for the stars

What will it take to launch an interstellar mission to Proxima b? Feature: First tip to the stars; Breakthrough Starshot program

07:51 Hydrogen result queried

Researchers claim to have made the long-sought ‘metallic’ hydrogen, but others are sceptical. Research paper: Dias and Silvera; News: Physicists doubt bold report of metallic hydrogen

15:11 Research Highlights

Downpours could change with climate warming, and Salmonella makes its host eat. Research Highlight: Salmonella makes hosts eat; Research Highlight: Lasting heavy rains to come

17:07 Beaks bolster bird theory

A single rare event could have prompted the speedy diversification of bird lineages. Research paper: Thomas et al.; News and Views: Catastrophe triggers diversification

22:34 News Chat

Scientists affected by Trump’s executive order on immigration, and using human-animal chimaeras in research. News: Meet the scientists affected by Trump’s immigration ban; News: The hybrid zoo

Never miss an episode: Subscribe to the Nature Podcast on Apple Podcasts, Google Podcasts, Spotify or your favourite podcast app. Head here for the Nature Podcast RSS feed.

doi: https://doi.org/10.1038/d41586-019-02037-1

Transcript

Bird beaks show how evolution shifts gear, getting to Proxima b, and have physicists made metallic hydrogen?

Interviewer: Kerri Smith

Coming up: what will it take to launch the first mission to another star system?

Interviewee: Gabriel Popkin

Forget about the rockets, the space shuttle, all that stuff. The craft itself will be tiny.

Interviewer: Adam Levy

And, a new paper claims to have created the elusive metallic hydrogen, but many physicists remain sceptical.

Interviewee: Ike Silvera

They can go ahead and try it. If they try it, they're either going to confirm it or show that it didn't happen.

Interviewer: Kerri Smith

Plus, what thousands of bird beaks can teach us about evolution. This is the Nature Podcastfor February 2nd, 2017. I'm Kerri Smith.

Interviewer: Adam Levy

And I'm Adam Levy.

[Jingle]

A group of physicists backed by $100 million pledge by a Russian investor are planning a trip to our nearest exoplanet. Kerri put together this report on their interstellar mission.

Audio Clip:

Stephen Hawking: We are here today to talk about Breakthrough Starshot and our future in space.

Interviewer: Kerri Smith

This is Stephen Hawking speaking in April 2016. He's on stage with a bunch of other scientists and the internet investor Yuri Milner, announcing the Breakthrough Starshot project.

Audio Clip:

Stephen Hawking: The limit that confronts us now is the great void between us and the stars. Today, we commit to this next great leap into the cosmos.

Interviewer: Kerri Smith

The next great leap will be interstellar. Breakthrough Starshot is aiming to develop the technology needed to get a spacecraft to our nearest star system, Alpha Centauri. There it will fly past an object of particular interest.

Audio Clip: [Music] Scientists say they have found the closest place outside of our solar system that could conceivably support life.

Audio Clip: The most exciting exoplanet discovery ever?

Audio Clip: It's been hiding right under our noses.

Audio Clip: An earth-sized planet.

Audio Clip: Proxima B.

Interviewer: Kerri Smith

Proxima B was announced in August 2016, just a few months after the Starshot announcement. It was a gift; there was already a NASA program and a handful of other projects researching how to go interstellar. Starshot has the same concept, but more money, and Proxima B was a natural destination. A feature in Naturethis week examines the interstellar voyage's to do list, but first, here's a description of the plan from Gabriel Popkin, author of the feature.

Interviewee: Gabriel Popkin

Forget about the rockets, the space shuttle, all that stuff. The craft itself will be tiny. It will be like, you could imagine, a small smartphone attached to a sail. On the ground, you're gonna have this extremely powerful laser that shoots up into the sky. Laser light bounces off the sail, and when it does that it pushes the sail.

Interviewer: Kerri Smith

So, that's the plan. Laser this thing into space and speed it up to one-fifth the speed of light, but this craft is built, equipped, and propelled by technologies that haven't been invented yet. Here's Philip Lubin, an astronomer on the Starshot committee who's also working on NASA's equivalent to the program.

Interviewee: Philip Lubin

This is not a simple program. It's the order, I would say, of a 30-year effort to really pull this off.

Interviewer: Kerri Smith

So, what will it take to get a spacecraft ready for a journey to Proxima B? What kind of timeline could we imagine for what needs to happen and when?

[Music]

Interviewee: Steve Mirsky

Come join us on a trip to the unspoiled destination, Proxima B. Only 4.2 light years away. That's just 20 years' transfer time for a craft as light as ours. Only a handful of advances are needed to propel us to our nearest star. 2017 to 2025: miniaturize electronics to fit the onboard chips. These chips will help the craft navigate and perform measurements.

Interviewee: Philip Lubin

The fact that you carry around with you in your pocket a smartphone which you take for granted… 50 years ago, if you go back to the year 1966, such a device would have been considered to be lunacy.

Interviewee: Gabriel Popkin

If the trend in electronics miniaturisation continues just for a few more years, they may be where they need to be.

Interviewee: Steve Mirsky

2017 to 2035: develop powerful lasers to accelerate the craft to interstellar velocities.

Interviewee: Gabriel Popkin

The most powerful lasers right now of the type that they need put out about 100,000 watts, and they need to increase that by a million.

Interviewee: Philip Lubin

Laser amplifiers, in particular, have been increasing in performance exponentially with a doubling time of performance about every 18 to 20 months.

Interviewee: Steve Mirsky

But don't get too trigger happy with those bright lasers until you've laser-proofed your craft.

Interviewee: Philip Lubin

How do you develop an ultra-low mass space craft and the relevant matching reflector that allows the light to propel the spacecraft, not burn up the space craft in the process?

Interviewee: Steve Mirsky

2040: Starshot leaves earth. Our trip is underway, but don't bother getting your camera out yet. There's dust and debris and then several years of nothing before we reach our destination. Oh, here comes the Oort Cloud. There may be some turbulence.

Interviewee: Gabriel Popkin

Beyond Pluto and all the objects that we've really studied, there's a big cloud of objects, and this is where some of our comets come from. People don't really know very much about the Oort Cloud because we can only study the occasional comet that gets kicked out. It's probably full of billions, if not trillions, of comet-like objects and there's no way to prevent the craft from hitting one.

Interviewee: Steve Mirsky

2048, our flight through the Oort Cloud is complete. 2050: nothing happens. 2055: nothing happens. 2060: Starshot reaches Alpha Centauri. Better get your cameras working fast because we're not slowing down. We'll be flying past Proxima B for just two hours.

Interviewee: Gabriel Popkin

It would take another four years to send the data back to earth. So that would put us at 2064. I'll be 83 years old at that point. I'd really love to see this data, [laughs]to live long enough to see it.

Interviewee: Philip Lubin

In the beginning, I told everybody who wants to hear it that I'm not gonna be alive when this thing gets off the ground, literally. That doesn't bother me at all. I'd be content to see it begun and to work on the technical details in between even if I'm not around to actually see the first pictures.

Interviewee: Gabriel Popkin

The chance of them getting their craft to Alpha Centauri by 2060, I would give them less than 50 percent odds on that. Even if they don't quite make it to Alpha Centauri as quickly as they hoped to, they might still create a means of exploring space that adds a lot to what we have now.

Interviewee: Philip Lubin

This is many more uses than simply the ability to send tiny spacecraft out to the stars.

Interviewee: Kerri Smith

Thank you to Philip Lubin of the University of California, Santa Barbara and Gabriel Popkin, freelance writer based in Washington, D.C. The voice of the Starshot travel brochure was the wonderful Steve Mirsky on loan from Scientific American's podcast. Check out his work at sciam.com/podcast.

Interviewer: Adam Levy

Hydrogen is the simplest and most abundant element in the universe. Just one proton, just one electron, but despite its simplicity there's still plenty scientists don't know about hydrogen. Under normal conditions on earth hydrogen exists in pairs: two hydrogen atoms bound together to form a molecule, H2. But hydrogen can also form a metal, a solid or liquid material where the electrons are free to wander. At least, that's what theorists predicted over 80 years ago.

Problem is, the pressures required to create so-called metallic hydrogen are incredibly tough to reach, millions of times higher than the pressure at the surface of the earth. For decades, physicists have been working to create the elusive metallic hydrogen. Only last year, Kerri spoke with Phil Dalladay-Simpson of Edinburgh University, who had just squashed hydrogen hard enough to create a new phase, a stepping stone on the way to the metallic state.

Interviewee: Phil Dalladay-Simpson

So it looks like we're on the cusp of reaching this metallic state.

Interviewer: Kerri Smith

Now, this might seem like a naive suggestion, Phil, but just squeeze it harder and see what happens.

Interviewee: Phil Dalladay-Simpson

Well, the problem is these experiments are very hard to get to these pressures. So this might actually be the technical limit from the apparatus.

Interviewer: Adam Levy

But now, a year on, a new team with a different apparatus say they've managed to overcome this limit. Their results, published in Science,have created both excitement and controversy. I called up co-author Ike Silvera to see why creating metallic hydrogen is worth all this effort in the first place.

Interviewee: Ike Silvera

We want to understand this on fundamental grounds, and that gives a good benchmark for a theorist to know which of their calculations are correct. The second thing is that it's been predicted that it will be a high temperature, possibly room temperature super conductor, and this would be fantastic. There's no other – no substance that's known – that conducts electricity without dissipation at room temperature.

Interviewer: Adam Levy

So to try and create metallic hydrogen, how do you actually go bout generating these immense pressures?

Interviewee: Ike Silvera

We use diamonds. Diamonds are the hardest material that we know. So we take two diamonds, and then you push the diamonds together. You have to get to a sufficiently high pressure for the transition to take place, and what's happened in the past is that before you get to a pressure where it becomes metal, the diamonds break. And so, we decided to put a big focus on getting to the highest pressures, and we changed a lot of the techniques that we and others had been using in the past.

Interviewer: Adam Levy

As you ramp up the pressure, how does it change? What do you actually see happening to the hydrogen?

Interviewee: Ike Silvera

As we turn the pressure up, we could monitor what's happening to the sample, and we found that at lower pressures, it was transparent to light. As you get up to really high pressures, the sample actually becomes black, and then when we turn the pressure up even higher, suddenly, it becomes reflective, luster-y, and that's the quality of a metal.

Interviewer: Adam Levy

This reflective appearance is why Ike reckons they finally created metallic hydrogen. This would be the first and only sample of this substance on earth and potentially the first room temperature super conductor able to conduct electricity without loss of energy. But other researchers aren't celebrating. In fact, rather the opposite. I caught up with Nature reporter Davide Castelvecchi to find out the word on the scientific street.

Interviewee: Davide Castelvecchi

I spoke to most of the competitors of the people who are actually trying to do the same thing and who know what the challenges are, and they are not convinced at all.

Interviewer: Adam Levy

Is there a possibility that they're just holding out and hoping that they might be able to do it, and there's some element of jealousy, or did they specify some pretty specific complaints about this setup?

Interviewee: Davide Castelvecchi

There have been, very consistently, a number of complaints that all these other experts have raised about the experimental methods in this paper and the fact that there's not enough data shown, the fact that they've only essentially done the experiment once on one sample, and they haven't even tried to repeat it.

Interviewer: Adam Levy

In this paper, they say they see the hydrogen change into a reflective state, indicating that it's gone into this metallic state, reflecting like a metal. What are the sceptics saying explains this, if not hydrogen turning into a metallic state?

Interviewee: Davide Castelvecchi

Well, there's two things. One, they don't really believe the measurements of shininess. The other is that they say, "We're not even sure that there is still hydrogen at that point because the hydrogen could have escaped from the diamond anvil, and maybe what we're seeing is some contamination maybe."

Interviewer: Adam Levy

Say that they actually have genuinely managed to create metallic hydrogen. What do you think it would take to convince these skeptical competitors of it?

Interviewee: Davide Castelvecchi

My feeling is that the level of mistrust seems so high that even if the same group comes up with a new paper with more data, at this point, I suspect that that won't be enough.

Interviewer: Adam Levy

So it'd have to be another group repeating these kinds of results?

Interviewee: Davide Castelvecchi

Right.

Interviewer: Adam Levy

So, of the people you spoke to, is the mood kind of excited to try and prove this wrong or prove it right, or is there a kind of frustration that there's a lot of attention going to this thing that these competitors don't necessarily feel is right?

Interviewee: Davide Castelvecchi

There is immense frustration. The people I talked to said this should not have been published. At the same time, there is a feeling in the field that after more than 80 years, we are on the brink of finding metallic hydrogen.

Interviewer: Adam Levy

In spite of all the doubts Davide has heard about whether metallic hydrogen has indeed been created, Ike Silvera is taking the criticism with a large pinch of salt. Instead, he's eagerly awaiting efforts from other groups to repeat his work.

Interviewee: Ike Silvera

We have people in the field that are sceptical and people in the field that are lauding our accomplishment, and it turns out that the people in the field that are sceptical are competitors of ours, and they've made comments like, "I don't believe that you can get that high of a pressure. Fine, we've shown what we've done. We've shown how to do it, and in our paper we show all the techniques. So they can go ahead and try it. If they try it, they're either going to confirm it or show that it didn't happen. I'm confident that they'll find that it happens.

Interviewer: Adam Levy

That was Ike Silvera, who's at Harvard University in Cambridge, U.S. His paper is available in the journal Science, Sciencemag.org. You also heard from Nature reporter, David Castelvecchi, who has written a metallic hydrogen news story, as well as Edinburgh University post graduate student Phil Dalladay-Simpson.

Interviewer: Kerri Smith

Still to come in the News Chat, we take a look at the impact of Trump's immigration executive order on researchers, but now Noah Baker joins us to read this week's Research Highlights.

Interviewer: Noah Baker

If you catch a bacterial infection, it's common to lose your appetite, but catch salmonella and you might just find that you keep munching. Researchers found that a protein produced by salmonella stops its host’s appetite from dropping too much. They gave mice either salmonella or a mutant strain that couldn't produce the protein. The mice with the regular bug had more of the protein in their faecesthan those with a mutant strain. Salmonella could be using this appetite trick to help spread to new hosts as well as to keep its current host alive. Find that paper in Cell.

As the world warms, the atmosphere heats up, and that means it holds more water. So, downpours are expected to become more intense, but does that increase the actual amount of rain? After all, the storms might get more intense, but shorter. A group looked at how three degrees of warming could change extreme rainfall events. They predicted that, for most regions, there would be more rain in heavy downpours. In fact, the extra rain pushed many storms over the threshold into being extreme events by today's standards. This heavy rainfall could make adapting to climate change a tough task. Read more in proceedings of the National Academy of Sciences.

Interviewer: Adam Levy

Before we jump back into the show, we just wanted to remind you that the Nature Podcastisn't the only way to hear from us. Make sure to subscribe to the Nature Video Channelon YouTube. You can find that at the helpful URL: YouTube.com/naturevideochannel.

Interviewer: Kerri Smith

And make sure to follow us on Twitter @NaturePodcast. For slightly more Kerri Smith themed Tweets, it's @miniKerri.

Interviewer: Adam Levy

And I'm @climateadam. Speaking of Tweets, this next piece is all about bids. You may not know this, but podcast reporter, Shamini Bundell is a bit of a secret twitcher, that is, somebody who likes bird watching. So, when she heard about a paper on bird beaks, she flew at the chance to interview the author, Gavin Thomas from the University of Sheffield. Gavin has been studying evolution on a grand scale. He wanted to know if 3D scanning thousands of bird beaks could reveal any big patterns, patterns which could help explain the complex evolutionary history of our feathered friends.

Interviewee: Gavin Thomas

So there's a lot of interest at the moment in trying to understand the diversity of life, so trying to, for example, ask why there are so many different types of species, but also the way in which those species differ.

Interviewer: Shamini Bundell

Didn't Darwin kind of figure that one out a while ago? Have we not got the answer? Natural selection. There you go, done.

Interviewee: Gavin Thomas

To an extent, that's true, yes. So, natural selection provides a mechanism for how species evolve over generations and perhaps over tens to hundreds of years. But then if we're thinking about really long-term effects, so how species have accumulated over millions or tens of millions of years, then natural selection doesn't always play out. They're trying to understand how natural selection scales up. There's a particular challenge that maybe is less frequently thought about at the moment.

Interviewer: Shamini Bundell

So, you're looking for much bigger patterns than are usually studied, and this is what you referred to in the paper as macroevolution. So instead of asking how a particular trait evolves in a species, you are asking how an entire group of species arises. Are there any overall patterns? The group you picked was birds, and why this example, and how did you get the data you need?

Interviewee: Gavin Thomas

We're working with birds, which are a particularly well-studied group and are particularly well-represented in natural history museums. So we've been measuring the shape of the bill in birds, and the reason that we focus on bird bills is that it's a nice structure. It's relatively easy to measure, but they tell us a lot about the way that the bird uses its environment in terms of their diet and the way that they forage. So that's telling us about their ecological niche.

Interviewer: Shamini Bundell

This might be a stupid question, but is there a different between a bill and beak?

Interviewee: Gavin Thomas

No. Bill and beak tend to be used quite interchangeably.

Interviewer: Shamini Bundell

So you had all these beak measurements from museum specimens. It was actually 3D scans?

Interviewee: Gavin Thomas

Yes, that's right.

Interviewer: Shamini Bundell

So really detailed information about the exact shape?

Interviewee: Gavin Thomas

Yes. So, for this paper we had scans for more than 2,000 species. A lot of the processing of that data has been done by volunteers. We're hoping eventually to have at least all living bird species, which would be around 10,000 scans.

Interviewer: Shamini Bundell

You have all this data. What kind of patterns did you see in it?

Interviewee: Gavin Thomas

One of the main results in the paper is the idea that early on in the history of birds, there's a really rapid accumulation of different types of bills. So the shape of the bird bill is changing very rapidly early on. So this is where the weird bird groups evolve: things like pelicans and flamingos and spoonbills and so on, have evolved rapidly early on. But then once you've evolved into these unusual bill shapes, what happens thereafter is just relatively minor tweaking of the same thing. Essentially, it's just kind of filling gaps. So you have, overall, this leads to a pattern of rapid early evolution and then a slow-down.

Interviewer: Shamini Bundell

And was that what you expected to find?

Interviewee: Gavin Thomas

It's long been hypothesised that you have an early burst-like pattern, but it's something that has genuinely only been tested within relatively small groups of species, but it's not really been tested extensively, particularly with ecologically-relevant data with measurements like the bill measurements that we've been taking.

Interviewer: Shamini Bundell

And this beak pattern you've found is a macroevolutionary pattern. Why is looking at this larger scale, instead of just microscale evolution, important?

Interviewee: Gavin Thomas

We think this is important because if we just assumed that microevolution scales to macroevolution, then we wouldn't expect to see lots of variation in the rate of evolution across major groups. But the fact that we do tells us that something different is going on.

Interviewer: Shamini Bundell

And these ideas of patterns, is that something that you'd be interested in applying to other groups or looking for these patterns in other groups?

Interviewee: Gavin Thomas

So, we focused on birds here, but what we really need to know now is whether these are the sorts of patterns – that we've observed – are the things which are idiosyncratic and just limited to birds, or whether it's something which is a much more general pattern where we have these bursts of evolution early on in large clades.

Interviewer: Shamini Bundell

Are there any practical applications to understanding these kind of evolutionary patterns?

Interviewee: Gavin Thomas

Potentially. So, there's an idea that specialised species might be at greater risk of extinction, and so we can use the data that we have on bill shape to ask whether ecologically unusual species are also those species that are currently threatened with extinction.

Interviewer: Shamini Bundell

And maybe identify species that are at threat?

Interviewee: Gavin Thomas

Yeah, so we could potentially identify species that we don't currently recognise as being threatened, but potentially could be given how specialised they are.

Interviewer: Adam Levy

That was Gavin Thomas at the University of Sheffield talking to reporter Shamini Bundell about his new paper. I think she was winging it a bit, but I have no "egrets" about giving the story "top billing." If you want to find out more about that "egg-cellent" paper, then you'd better "flamin-go" and find it on the Naturewebsite, Nature.com/nature.

Interviewer: Kerri Smith

And do feel free to Tweet us @NaturePodcast if you have any more "fowl" puns. Time now for this week's News Chat, and we have a special guest with us in the London studio. Jane Lee is here from Washington, D.C. where she is the assistant U.S. news editor. Welcome, Jane.

Interviewee: Jane Lee

Thanks. Good to be here.

Interviewer: Kerri Smith

Now, it's not going to surprise anyone that our first topic is Trump. One of his executive orders from last week has had large ripple effects already on people being able to go to the U.S.

Interviewee: Jane Lee

Right. So he signed an executive order last week that bars refugees for 120 days, but refugees from Syria indefinitely, and then the order included barring citizens from 7 Muslim-majority countries compromised by terrorism for 90 days.

So, those countries are Iran, Iraq, Libya, Somalia, Sudan, Syria, and Yemen. And that's had some immediate effects for researchers in the United States who are citizens of those countries, either being unable to travel outside the U.S. to conferences and such, for fear that they might not be able to get back in, or relatives come visit them in the States.

Interviewer: Kerri Smith

So science obviously is an international enterprise. Naturehas been looking into some of the stories of those affected by it. What are some of the stores in the piece?

Interviewee: Jane Lee

There's a molecular geneticist who is finishing a post doc at the Harvard Medical School. He was preparing to go out in the job market and hoping that conference talks would give him much-needed exposure, but now… He's an Iranian citizen, and he worries that if he leaves the U.S., he might not be able to come back.

There is another researcher in Philadelphia who – he's an Iranian citizen with a green card, which means that he can live and work permanently in the United States. He's not able to visit his sick mother in Iran now for fear that he might not be able to get back.

Interviewer: Kerri Smith

What might be – what's your best guess at the long-term effects of something like this after the 90 days have elapsed?

Interviewee: Jane Lee

Well, that's a hard one because it's unclear what's going to happen after 90 days, 120 days. Several groups have launched lawsuits in the United States protesting these executive orders. It's unclear what the knock-on effects could be for international scientific collaborations like CERN or international collaborations just between individual scientists. Hopefully, there isn't a kind of brain drain or siphoning off of expertise and researchers from the United States, although I've seen articles, opinion articles in other countries' newspapers saying, "It's time to seize the talent that the U.S. seems to be turning away."

Interviewer: Kerri Smith

And there is also on the website, an interview with John Holdren, Obama's science advisor, who has become a little looser-tongued since leaving office.

Interviewee: Jane Lee

Yeah, he's called the executive order perverse and an abomination and a terrible, terrible idea. He's gone on to say that this immigration stance could undermine all the international science ties that Obama sought to build during his time in office. Reduced amounts of scientific collaboration means that we might not get notice on influenza outbreaks in other countries that could directly affect the U.S.

Interviewer: Kerri Smith

Because after all, Trump can't isolate himself from everything, including flu, I suppose. Now, we're going to move on to a more purely science story, which some listeners who don't like it when we talk about Trump, will much prefer. This is a story about a trend in biology, to use chimeras. What's a chimera, first of all?

Interviewee: Jane Lee

So, chimera is a human-animal hybrid. It's a combination of human cells and pig cells, for instance, or human cells and cow cells, for instance. Due to ethical regulations, they're not brought to term, but during the time that the researchers have them in the lab, they can look at the placement of the human cells, where they've gone, how many survive and are in the embryo, and they can help researchers in the future hopefully with human organ transplants, drug discoveries, and other types of basic research.

Interviewer: Kerri Smith

So you can insert a human cell into a blob of cells from a different creature and, I don't know, grow them better or see how they develop or –

Interviewee: Jane Lee

Right. So they take pluripotent stem cells, which are basically these cells that can turn into anything in the body. So, a heart, skin cells, muscles, things like that, and they inject those human stem cells into a mouse egg or a cow egg, and then grow them to the point to see if the embryo starts to grow human organs. So the human-pig hybrid, the embryo is only allowed to grow to about three or four weeks, but then during that time, the researchers were able to look at – they had modified the human cells with a green fluorescent protein so they could just track where they went.

It was actually only about 1 in 100,000 of the cells in the pig-human hybrid were human cells, but in other animal combination, so a mouse-rat combination, they actually were able to grow rat organs within a mouse body.

Interviewer: Kerri Smith

What would be the kind of ten-year goal or the long-term goal for the researchers of doing this kind of study?

Interviewee: Jane Lee

I think eventually they would like to get to the point where they could grow a human organ in an animal for transplantation into a person, and so right now there's a long list of people waiting for organs on the donor list. Once they're lucky enough to get an organ, I mean, they have to deal with a life-long regimen of immunosuppressant drugs, and there's always a fear that the body is going to reject that organ. But if you can transplant an organ into someone made up of their own cells, you don't have that problem. You don't have to wait for the hope of maybe getting an organ. You can grow one or have one grown for you.

Interviewer: Kerri Smith

For more details on all of the stories we've mentioned – Trump's executive order on immigration, the John Holdren interview, and the story of chimeras – you can find more at Nature.com/news. For the latter story on chimeras, that paper came out in Cell.

Interviewer: Adam Levy

That's all we have time for this week, but if you haven't got your podcast fill, make sure to look out Backchat. That came out a few days on the RSS feed. I'm Adam Levy.

Interviewer: Kerri Smith

And I'm Kerri Smith.

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