Podcast Summary: "Selects: How Extinction Works"

Stuff You Should Know — iHeartPodcasts
Hosts: Josh Clark & Charles W. "Chuck" Bryant
Air Date: November 1, 2025

Episode Overview

In this "Selects" episode, Josh and Chuck revisit their popular 2014 deep dive into extinction—how it occurs, why it’s a natural part of life on Earth, and how human activity may be ushering in a new mass extinction. The duo breaks down scientific theories, discusses key extinction events from the past, and examines the complications (and controversies) around de-extinction and current biodiversity loss. The episode is peppered with their signature blend of humor, pop culture references, and accessible science explanations.

Key Discussion Points & Insights

1. Setting the Stage: Extinction as a Process

• Extinction is introduced as a normal part of the evolutionary process, not just a modern tragedy.
• Historical context: For most of scientific history, extinction was denied, largely for religious reasons.
  • Quote: “For a very long time, I guess, scientists believed that God created all the animals on Earth and that his will was too perfect…to even allow for extinction.” (Charles, 06:49)

Notable Figures:

• Georges Cuvier (1812): Asserted extinction was real and caused by cataclysmic events ("Especis perdus" or "Lost Species"). (07:23)
• Charles Darwin: Allowed for extinction, but saw it as a gradual process. This slow view dominated until late 20th century. (08:20)

2. Scientific Shifts: Sudden Extinction Events

• Mass extinctions can happen abruptly, not just slowly over time.
• Alvarez Hypothesis & the Dinosaurs:
  • In 1980, Walter Alvarez linked a clay layer full of iridium (rare on Earth, common in asteroids) to the end of the dinosaurs, proposing an asteroid impact 65 million years ago.
  • Confirmation came in 1991: A massive crater was found under the Yucatan, matching the extinction timeline. (09:05–10:57)

3. The “Big Five” Mass Extinctions

(29:09–34:45)

• The five recognized “mass extinction” events:

  1. Ordovician (c. 490mya): Rapid sea-level drop, loss of half of all animal families.
  2. Late Devonian (c. 360mya): Uncertain cause, about a quarter of marine families perished.
  3. Permian-Triassic (c. 250mya): “The Great Dying,” up to 96% of life gone—likely due to volcanic activity and acid rain.
  4. End-Triassic (c. 200mya): Marine life hard-hit, specifics still debated.
  5. Cretaceous-Paleogene (K–Pg, c. 65mya): Asteroid impact, end of dinosaurs.

• There’s no strict numerical definition, but the “you know it when you see it” rule applies—massive, rapid, global losses.

  • Quote: “There’s no real definition for it...these five were so massive that there’s virtually no debate.” (Charles, 33:28)

4. Background vs. Mass Extinction

• Typical (“background”) extinction rate is 1–5 species/year.
• Current rates estimate 100–1000 times greater due to human activity. (13:20–13:28)
• References: Elizabeth Kolbert’s "The Sixth Extinction," and other scientific articles & HowStuffWorks resources.

5. Human Impact & the Sixth Extinction

(40:11–48:49)

• Growing consensus we’re in the midst of a Sixth Mass Extinction (Anthropocene), driven by:
  • Habitat loss, overexploitation, pollution, invasive species, and climate change.
• Notable statistic: "Only 2% of rivers in the US run unimpeded. Everything else has been altered in some way." (Jerry, 47:22)
• Human actions causing "constant stress" rather than a single cataclysm, making current biodiversity loss unique—and potentially more damaging.
  • Quote: “Now there’s no stress relief, it’s just a constant. There’s no recuperation because it’s not over.” (Jerry, 35:21)

Sixth Extinction Causes:

• Overkill Theory: As humans spread, megafauna (giant animals) vanished, suggesting hunting and habitat destruction drove extinctions—debated but supported by correlation. (43:17)
• Climate Change Theory: Some argue natural climate cycles are primary, but modern rates and patterns point strongly to human involvement. (45:09)

6. De-Extinction & Rediscovered Species

• De-Extinction: Science can sometimes "bring back" extinct animals (e.g., Bucardo goat in 2003), but raises ethical and ecological questions.
  • Quote: “Just because we can, does that mean we should?” (Charles, 25:19)
• Lazarus Species: Some species, like the coelacanth and Cuban solenodon, thought extinct, were found alive—highlighting fossil record limitations. (19:52–21:49, 49:47–51:29)
• Risks of focusing on bringing species back instead of conserving those present are discussed.

7. Why Biodiversity Matters

• Ecosystem collapse can result from the disappearance of even small or seemingly unimportant species, due to complex food web interdependencies.
  • Examples: Bees (pollination), passenger pigeons, American buffalo. (23:28)

Notable Quotes & Memorable Moments

• Humorous Opener: “A viable living organism—one that, when we leave the studio, will probably become extinct.” (Chuck, riffing on the mix of scents in the studio, 03:02)
• On Scientific Humility: “We have no idea how many living species there are on the planet today. Or have been. It’s all just a good guess.” (Jerry, 21:49)
• On Human-Caused Change: “The world starts to try and recoup...with us, it’s constant stress, and no recuperation.” (Jerry, 35:21)
• On Oceans: “The drop in ocean pH levels that have occurred in the past 50 years… might exceed what’s happened in the past 50 million.” (Jerry, 48:49)
• Perspective: “All evidence is showing we are doing a lot to speed up extinction events...so much so that the big five is now possibly the big six.” (Charles, 36:55)

Timeline of Major Topics

| Timestamp | Segment Description | |-----------|---------------------------------------------------------------------| | 04:44 | Extinction: processes and misconceptions (religious/scientific) | | 06:00 | The coelacanth and "Lazarus species" concepts | | 09:05 | Acceptance of asteroid mass extinctions—the Alvarez hypothesis | | 13:20 | Normal vs. current extinction rates | | 19:49 | Rediscovered species and the coelacanth’s story | | 21:07 | "Pseudo-extinction" and fossil record challenges | | 23:28 | Biodiversity, ecosystem collapse, and human impacts | | 24:22 | De-extinction: science and ethical debate | | 29:09 | The "Big Five" mass extinction events | | 34:45 | How to define a mass extinction? | | 40:11 | Are we in the "Sixth Extinction"? | | 45:09 | Human-driven vs. natural (climate) causes—debate and data | | 47:52 | Human impacts: habitat change, CO2, ocean acidification | | 49:47 | Rediscovery of supposedly extinct animals ("Lazarus" examples) |

Takeaways

• Extinction is natural—but current rates are unprecedented and strongly linked to human activities.
• There is no unchanging baseline for life on Earth; ecosystems and dominant species shift constantly in response to extinction events—some gradual, some catastrophic.
• While de-extinction fascinates, the hosts caution against seeing it as a solution to current biodiversity loss.
• The "Sixth Mass Extinction" is not just a scientific concept but a real, pressing concern given ongoing human impact.
• The tension between hope (rediscovered species) and loss (mass extinction) runs through the episode’s tone, balanced by the hosts’ wit.

Further Reading / References

• Elizabeth Kolbert — "The Sixth Extinction" (book, New Yorker article)
• HowStuffWorks articles (notably "Will We Soon Be Extinct?" and "Why Is Biodiversity Important?")
• iO9 "Lazarus species" feature

Closing Thoughts

Josh and Chuck offer a nuanced, accessible exploration of extinction, mixing rigorous science, humor, and pop culture references. From mass extinctions long before humanity to the dilemma of de-extinction, listeners come away with a deeper appreciation for the fragility—and resilience—of life on Earth.

Note:
Advertisements and unrelated intros/outros were omitted from this summary. For the full episode and references, check Stuff You Should Know via iHeartPodcasts or your preferred podcast platform.