Why Some Species Survive Mass Extinctions

Summary

Summary of Short Wave Episode: "Why Some Species Survive Mass Extinctions"

Podcast: Short Wave (NPR)
Host: Bradley McCoy (guest host)
Date: November 5, 2025
Guest: Kemi Ashingiwa, Paleophysiology Graduate Student (Stanford University)

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Episode Overview

This episode delves into the science behind one of Earth's greatest mysteries: why certain species survive mass extinctions when others do not. Using the “Great Dying” (Permian-Triassic extinction) as a lens, host Bradley McCoy and guest Kemi Ashingiwa discuss new research revealing how physiological traits and environmental factors determined the winners and losers 251.9 million years ago—and what lessons we can draw for today’s warming, oxygen-changing world.

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Key Discussion Points and Insights

1. The Context: The Great Dying (Permian-Triassic Extinction)

• Background:
  • 251.9 million years ago, massive volcanic eruptions (Siberian Traps) unleashed enormous greenhouse gases, causing global temperature spikes and hypoxic (low-oxygen) oceans.
  • Nearly all species on Earth perished; the event is called the “Great Dying”—Earth’s biggest mass extinction.
  • Notably, some marine animals like bivalves (clams, mussels) survived, while others like brachiopods almost vanished.
• Quote:
  • Kemi Ashingiwa (01:27):

    "Temperatures go up, oxygen in the ocean goes down. Not everything dies, but almost everything dies."

2. The Central Mystery: Why Did Bivalves Survive?

• Bivalves and brachiopods seem similar—both are marine filter feeders with shells—yet their fates were drastically different.
• Quote:
  • Kemi Ashingiwa (02:19):

    "They both have shells, they're both filter feeders. But brachiopods almost no one has heard of because they almost all went extinct at the end Permian."

• Scientists have hypothesized:
  • Bivalves might be more tolerant of higher temperatures or low oxygen.
  • Competition and food quality could play a role.
  • Lack of quantitative, experimental data has hampered clear answers.

3. New Research: Testing Theories in the Lab

• Ashingiwa’s Experiments:
  • Compared modern relatives: bivalves vs. brachiopods.
  • Focused on their responses to:
    • Temperature
    • Oxygen levels
    • Sulfide (hydrogen sulfide, H₂S, produced by ocean bacteria in anoxic settings)
• Quote:
  • Kemi Ashingiwa (05:25):

    "Brachiopods are better at dealing with low oxygen... But when you increase the temperature, the, let's say, the quote-unquote advanced gills of the bivalve let them oxygenate themselves better, and they win out in the end."

  • For sulfide, bivalves were far more tolerant:

    "Bivalves are much, much better at dealing with sulfide than brachiopods are."

4. Experimental Methodology (08:30)

• Ashingiwa describes practical lab setup:
  • Batches of live bivalves and brachiopods were placed in:
    • Euxinic conditions (high sulfide, no oxygen)
    • Anoxic conditions (no oxygen, no sulfide)
    • Across various temperatures
  • Monitored survival over months.

5. Results and Interpretation (09:08)

• Brachiopods fare better than bivalves under anoxic/low-temperature settings.
• At higher temperatures—and especially with sulfide—bivalves clearly outperform brachiopods in survival.
• Quote:
  • Kemi Ashingiwa:

    "At low temperatures in anoxic settings, brachiopods ended up beating out bivalves. But then at higher temperatures, when you added sulfide, bivalves ended up surviving much, much better." (09:08)

6. Solving the Permian Puzzle

• These results support the idea that the survivors of the end-Permian extinction, like bivalves, had key physiological advantages for coping with:
  • High temperatures
  • Oxygen depletion
  • Increased sulfide—a triple whammy faced during mass extinctions
• Quotes:
  • Bradley McCoy (10:01):

    "The experiments indicate that bivalves are better able to deal with these stressors, which helps explain why they did so well post extinction—and why most people haven't heard of brachiopods."

  • Kemi Ashingiwa:

    "They got their butts kicked." (10:05)

7. Lessons for the Present (10:12)

• The multifactor stress of ancient extinctions mirrors modern challenges:
  • Anthropogenic climate change (greenhouse gases, warming, deoxygenating oceans) resembles ancient triggers.
  • The mix of stressors can be more lethal combined than alone.
• Notable Quote:
  • Kemi Ashingiwa (10:18):

    "What we have learned from our experiments, from these various models and all of these studies is that it's not just temperature that matters, it's not just oxygen that matters, it's not just sulfide that matters, it's all of these things together because their combined effects are so much worse."

• Urges caution for the present and future:
  • "We really want to limit our impact on the climate and on these ecosystems as much as possible because everything is interlinked... It would be a real tragedy for anthropogenic climate change to be the thing that knocks [brachiopods] out for good." (11:12)

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Memorable Moments & Notable Quotes

• On why we eat clams, not brachiopods:
  • Kemi Ashingiwa (02:09):

    "Which is why when you go to a seafood restaurant, there are mussels up the wazoo."

• On extinction’s evolutionary outcome:
  • Kemi Ashingiwa (10:06):

    "They got their butts kicked."

  • Bradley McCoy:

    "The winners write history, right?"

• On research motivation:
  • Kemi Ashingiwa (07:27):

    "[My lab] has an emphasis on synergistic effects between all of these different factors... that's important to investigate and interesting to study."

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[Bonus Segment] Science and Science Fiction (11:35 – 12:47)

• Kemi Ashingiwa, also a bestselling sci-fi author, says that writing and consuming science fiction keeps her curiosity alive amid the grind of lab work.
• Quote:
  • Kemi Ashingiwa (12:11):

    "I think writing science fiction and reading and watching really good science fiction helps me maintain this constant excitement about science and the work..."

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Key Timestamps of Important Segments

• 00:48–01:27 — Setting the Great Dying scene
• 02:09–02:35 — Introduction to the bivalve vs. brachiopod mystery
• 04:13–05:16 — Competing theories on why species survived
• 05:25–06:19 — Physiology difference and Ashingiwa’s recent findings
• 07:27–08:21 — Why study sulfide as a stressor
• 09:08–09:44 — Main experimental results
• 10:12–11:28 — How ancient lessons inform modern climate concerns
• 11:35–12:47 — The interplay between scientific research and science fiction writing

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Conclusion

In just under 15 minutes, this episode unveiled how cutting-edge research on primitive sea creatures and ancient extinctions can shed light on the multifaceted threats of present-day climate change. Through humor, informed discussion, and memorable analogies, Kemi Ashingiwa and Bradley McCoy explain why evolutionary winners aren’t always obvious—and why the survival lessons of the past hold crucial warnings for the species of the future.

Transcript

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[Bradley McCoy]

Hey, short waivers.

[Kemi Ashingiwa]

I have a free and quick favor to ask right now on the app or platform where you're listening.

[Bradley McCoy]

Could you leave us a rating or a review because it really helps new.

[Kemi Ashingiwa]

Listeners find our show and we read what people write. Like this listener who recently said quote, bite sized pieces of fascinating science news. It's now one of my go tos as a source of interesting non political news feedback like this helps us figure out what you like and what you don't. So leave us a review and keep listening to Short Wave. All right, onto the show.

[Bradley McCoy]

You're listening to Short wave from NPR. Hey Shortwavers producer Burley McCoy guest hosting. Today we're with an episode about a mysterious mass extinction.

[Kemi Ashingiwa]

So 251.9 million years ago there are these volcanoes that erupt and they pump all these greenhouse gases into the atmosphere.

[Bradley McCoy]

This is Kemi Ashingiwa. She's a paleophysiology graduate student at Stanford University. And this volcanic activity she's talking about wasn't just one or two eruptions. It was on the scale of a whole continent in what is now the Siberian Traps in Russia.

[Kemi Ashingiwa]

And as a result of this, there is global climate change. Temperatures go up, oxygen in the ocean goes down. Not everything dies, but almost everything dies.

[Bradley McCoy]

This mass extinction, Earth's third, is known as the Great Dying, though the official name is the Permian Triassic, or the end Permian mass extinction.

[Kemi Ashingiwa]

The End Permian is the largest loss of animal diversity in Earth's history.

[Bradley McCoy]

The vast majority of all species on land and at sea were wiped out, but a small percentage survive, like a class of marine filter feeders called bivalves.

[Kemi Ashingiwa]

Bivalves are essentially like clams, which there.

[Bradley McCoy]

Are a lot of on Earth relatively.

[Kemi Ashingiwa]

Which is why when you go to a seafood restaurant, there are mussels up the wazoo.

[Bradley McCoy]

Less triumphant, the tale of their distant cousins, the brachiopods.

[Kemi Ashingiwa]

They both have shells, they're both filter feeders. But brachiopods almost no one has heard of because they almost all went extinct at the end Permian.

[Bradley McCoy]

And the mystery is why did bivalves do so good when brachiopods almost went extinct?

[Kemi Ashingiwa]

We want to know how climate change impacts species on the scale of planets.

[Bradley McCoy]

Because Kemi says the conditions that led to the world's largest mass extinction, those volcanoes that erupted some 250 million years ago and spewed greenhouse gases into an ancient sky.

[Kemi Ashingiwa]

Those greenhouse gases is actually similar to anthropogenic cloud climate change.

[Bradley McCoy]

Today on the show, a mass extinction mystery. How scientists are looking to descendants from the great dying for clues that may help the species of today. You're listening to Shortwave, the Science podcast from NPR.

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[Bradley McCoy]

Okay, Kami, can you lay out the possibilities of why some species in this epic mass extinction called the Great Dying die out while a handful lived?

[Kemi Ashingiwa]

Okay, that is, that is the question. So at the end, Permian bivalves beat out their distantly related cousins, brachiopods. And one of the biggest questions for this extinction is how? And people suggested all sorts of things. People have talked about maybe bivalves are better at dealing with high temperature. Maybe bivalves are better at dealing with low oxygen. People have talked about competition and food availability, availability and the quality of this food. And so there are all these theories, but there's not as much quantitative data. And so that's where eco physiologists and paleo physiologists come in. We're trying to collect data, quantitative data to support these theories.

[Bradley McCoy]

Okay, and what, what have you learned from that data? Like, what are bivalves better at that brachiopods aren't, or vice versa?

[Kemi Ashingiwa]

So brachiopods are better at dealing with low oxygen, but then when you increase the temperature, the, let's say the quote, unquote, advanced gills of the bivalve let them oxygenate themselves better, and they went out in the end. So just to restate that, brachiopods are a bit better at dealing with low oxygen, but bivalves are better at dealing with high temperatures. When it comes to my own research, I recently finished up a study looking at the impact of sulfide on bivalves and brachiopods. And what I saw in this study was that bivalves are much, much better at dealing with sulfide than brachiopods are. And this could help explain potentially how bivalves were able to win out in the end.

[Bradley McCoy]

Okay, so your experiments are spec. Specifically looking at how clams versus brachiopods respond to sulfide. What is sulfide?

[Kemi Ashingiwa]

Yes.

[Bradley McCoy]

Where did it come from? And what's it doing to them?

[Kemi Ashingiwa]

Okay, so sulfide is H2S. It is this chemical that is produced by bacteria in anoxic settings.

[Bradley McCoy]

No oxygen.

[Kemi Ashingiwa]

No oxygen. Yeah. So essentially, when the end Permian happened, greenhouse gases resulted in this huge spike in temperature. It resulted in this huge decrease in oxygen. And these microbes that produce sulfide love anoxia. They love it when there's no oxygen. And so this deoxygenation happened. These microbes that produce sulfide were living it up. They produce tons of sulfide, and then you have a lot of sulfide in the ocean, and that put pressure on animals.

[Bradley McCoy]

I see. Okay, so what made you want to go this route? All the other things that could have been this kill switch. Why did you pick sulfide?

[Kemi Ashingiwa]

So there's been a lot of discussion about temperature, there's been a lot of discussion about oxygen, there's been a lot of discussion about sulfide. But there's a limited number of experiments on all three of these together, or even two of them together. And I think in the labs that I'm part of, there is definitely an emphasis on, you know, these synergistic effects between all of these different factors. And I think that's important to investigate and interesting to study. Yeah.

[Bradley McCoy]

And so are you looking at sulfide with other things?

[Kemi Ashingiwa]

Yeah.

[Bradley McCoy]

Are you like.

[Kemi Ashingiwa]

Okay, so with the study, I was looking at the impact of sulfide or the impact of euxineas. That's sulfide with no oxygen. I was looking at the impacts of anoxia, which is just no oxygen at all.

[Bradley McCoy]

No oxygen.

[Kemi Ashingiwa]

No oxygen at all. Yep. And I was looking at these effects on the species at a range of temperatures.

[Bradley McCoy]

Okay. And then briefly paint the picture of what your experiments look like. Like, you don't have a clam in your left hand. And like your.

[Kemi Ashingiwa]

Pretty much. With these experiments, I collected a bunch of bivalves and brachiopods, and then I put some into a euxine setting. So sulfide with no oxygen. And I put some into Anoxic settings. So no oxygen and no sulfide there. And I looked at their survival over a couple months at these different temperatures.

[Bradley McCoy]

And then what did you learn from your experiments?

[Kemi Ashingiwa]

Yes, what I ended up seeing overall was that at the low temperatures in anoxic settings, brachiopods ended up beating out bivalves. But then at higher temperatures, when you added sulfide, bivalves ended up surviving much, much better. And this indicates that bivalves are better able to deal with these added stressors that mass extinctions like the end Permian presented animals with.

[Bradley McCoy]

Okay, so at low temperatures, brachiopods good. High temperatures, sulfur bad.

[Kemi Ashingiwa]

Bracha bad. Yes.

[Bradley McCoy]

Okay, got it. And so then how does this work help us solve the mystery of what happened during the end Permian mass extinction?

[Kemi Ashingiwa]

So the experiments indicate that bivalves are better able to deal with these stressors, which helps explain why they did so.

[Bradley McCoy]

Well post extinction and why most people haven't heard of brachiopods.

[Kemi Ashingiwa]

Right. Because they got their butts kicked.

[Bradley McCoy]

The winners, right? History.

[Kemi Ashingiwa]

Yeah, the clams. The clams, the clams, yeah. Yeah.

[Bradley McCoy]

Now how could all of this together, your experiments, what you know from other researchers, help the species of today.

[Kemi Ashingiwa]

Yeah. So mass extinctions provide a lot of critical information about how climate change, changes in temperature, changes in oxygen, changes in things like sulfide, how those changes animal life and life in general. And so what we have learned from our experiments, from these various models and all of these studies is that it's not just temperature that matters, it's not just oxygen that matters, it's not just sulfide that matters, it's all of these things together because their combined effects are so much worse. And I think it means that climate change is an extremely tricky problem, an extremely complicated problem, and we really want to limit our impact on the climate and on these ecosystems as much as possible because everything is interlinked. I think brachiopods have been around for a really, really long time. They survived the end Permian, and it would be a real tragedy for anthropogenic climate change to be the thing that knocks them out for good.

[Bradley McCoy]

Kemi, thank you so much for chatting with me today.

[Kemi Ashingiwa]

Thank you so much for having me today.

[Bradley McCoy]

This episode was produced by Hannah Chin and edited by our showrunner, Rebecca Ramirez. Tyler Jones checked the facts and Jimmy Keeley was our audio engineer. Beth Donovan is our Vice president of podcasting. I'm Bradley McCoy. Thanks for listening to Short Wave from NPR. Aside from pursuing a science PhD, you are also a bestseller selling sci fi author. You've said that you get a lot of your sci fi ideas from your science, which I get makes sense. I'm wondering, does it ever work the other way around?

[Kemi Ashingiwa]

I would say yes, absolutely. I think writing science fiction and reading and watching really good science fiction helps me maintain this. I think constant excitement about science and the work. I think it's easy to get lost in the nitty gritty of of experiments when you've spent, you know, like 10 hours in the lab. But I definitely use science to inspire my fiction and I definitely use the media that that I love to, I think bolster my excitement for science.

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