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)

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.

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)

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."

[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..."

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

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.