Podcast Summary: Short Wave – “Toxic? These Animals Don't Care”

Host: NPR (Regina Barber)
Guest: Dr. Shabna "Shab" Mohamadi, Evolutionary Biologist
Date: August 19, 2025

Episode Overview

This episode of Short Wave explores the surprising story of cardiotonic steroid toxins—compounds made famous by poisonous toads, dangerous plants, and even classical art. Host Regina Barber chats with Dr. Shabna Mohamadi (“Shab”), whose career has focused on how both animals and humans interact with (and sometimes resist) these deadly poisons. The episodes dives into the science of adaptation, the wild diversity of toxin resistance, and unexpected connections to human health—from gut microbes to male contraception.

Key Discussion Points & Insights

1. Cardiotonic Steroids: Toxicity & Biological Effects

• Toxins as Defense: Many plants and animals, like certain toads in South America, produce cardiotonic steroids—a class of toxins so powerful that they can kill predators by disrupting the sodium-potassium pump in cells (00:18-01:13).
  • “When they're ingested and they reach the bloodstream...they bind to and disable...the sodium-potassium pump. It plays a role in almost every single physiological system: blood pressure regulation, cardiac contractility, brain function.” — Dr. Shabna Mohamadi (00:47)
• Wide Diversity: There are “hundreds of different kinds of these toxins,” present in everything from plants to insects (01:13).

2. Human Use of Toxins

• Ancient Medicine: Humans have co-opted carditonic steroids medicinally since ancient Egypt, using them to treat heart failure (01:43-02:14).
  • “To this day, we still do that. Actually, some versions of cardiotonic steroids are prescribed for treating congestive heart failure.” — Shab (02:11)

3. Gut Microbes and Toxin Resistance (03:05-04:49)

• Microbial Defense: Not all humans absorb the same amount of toxin due to the presence of certain gut bacteria that can break them down.
  • “…there is a bacteria in our gut. Not everybody has it, and some people have more of it than others. This bacteria can actually metabolize cardiotonic steroids…they break it down so that less ends up getting absorbed in your blood.” — Shab (03:35)
  • “Thanks to our gut bacteria. As long as you have a good, healthy gut flora.” — Shab (04:42)

4. Vincent Van Gogh and Foxglove: Art Meets Poison (04:49-06:07)

• Artistic Impact?: There’s a theory that Van Gogh ingested foxglove (source of digoxin, a cardiotonic steroid) that might have influenced his vision and thus his art.
  • “One of his famous paintings…his doctor…next to him is a plant, and this plant is the foxglove…it produces the cardiotonic steroid digoxin…” — Shab (04:55)
  • “One of the rare [side effects]…is seeing bright halos around lights…like Starry Night.” — Shab (05:41)
  • “Maybe the reason why he painted the way he did…was because he was recreationally consuming cardiotonic steroids.” — Shab (05:53)

5. How Animals Weaponize or Resist the Toxin

• Defense Mechanisms:

  • Toads synthesize toxins from cholesterol, storing them in skin glands (06:20).
  • Other animals engage in sequestration, using toxins from their prey to defend themselves (European hedgehogs, African crested rats, monarch butterflies) (07:00-08:00).
  • “Monarch butterflies…caterpillars feed on milkweed and they…take the cardiotonic steroids…store it in their own body.” — Shab (07:21)
  • “The European hedgehog…chew[s] on toad skin…lick[s] it onto their spines…” — Shab (07:34)
  • “African crested rat…their hairs have these hollow spaces and those spaces can wick the toxin into the hair.” — Shab (07:49)

• Predator Resistance:

  • Some predators (birds, snakes) have developed ways to eat toxic prey without absorbing toxins—like eating only the non-poisonous parts (08:11).
  • “Birds…just eat the insides of the toad and leave the skin out. They know that the skin is toxic.” — Shab (08:18)
  • “Snake in Asia…do it with their mouths…bite around in the stomach area and get that out and leave the skin behind.” — Shab (08:25)

• Convergent Evolution:

  • Multiple unrelated organisms evolve the same resistance mechanism—specific mutations at nearly the same site on the sodium-potassium pump (08:58-10:12).
  • “All of these animals…have evolved resistance…by one or two mutations at the same place on the sodium-potassium pump…[but] through different mutations, but it’s always at the same site.” — Shab (09:43)

6. Lab Research: Reconstructing Evolution (10:12-11:19)

• Experimental Evolution: Shab's lab uses statistics and genetics to resurrect ancient proteins in the lab and test at what point resistance mutations would have been possible.
  • “…we can reconstruct the gene for this protein 60 million years in the past…Then we resurrect that in the lab…[and] move modern resistance mutations back in time…to see how the effects change…” — Shab (10:39)

7. Human Applications: Birth Control

• Male Contraception Research: Targeting sperm-specific sodium-potassium pumps—using derivative toxins—inspired by the evolutionary arms race between toxins and resistance (11:31-12:49).
  • “…if they can disable only copy number four [of the sodium potassium pump, specific to sperm], then they can disable sperm.” — Shab (12:33)

Memorable Quotes

• “Toxicity…can feel ubiquitous in this world, and yet some predators have learned to overcome it. How do they do it? And what does all of this have to do with Vincent Van Gogh?” — Regina Barber (02:14)
• “Thanks to our gut bacteria. As long as you have a good, healthy gut flora.” — Shab (04:42)
• “All of these animals…have evolved resistance to cardiotonic steroids by one or two mutations at the same place on the sodium-potassium pump.” — Shab (09:43)
• “We do this at the gene level so we can reconstruct the gene for this protein 60 million years in the past…” — Shab (10:39)
• “If they can disable only copy number four, then they can disable sperm.” — Shab (12:33)
• “We went from, you know, predators eating toxic animals to Vincent Van Gogh to male contraception. I loved this.” — Regina Barber (12:49)

Notable Timestamps

• 00:18-01:13 — Introduction to cardiotonic steroids and their function.
• 02:14 — Setting up the episode’s central mysteries.
• 03:05-04:49 — Gut microbes and resistance to toxins in humans.
• 04:49-06:07 — Van Gogh, foxglove, and art influenced by toxins.
• 06:20-08:00 — Toxin production and usage in animals for defense.
• 08:11-10:12 — How predators develop resistance (mechanical and genetic); convergent evolution.
• 10:12-11:19 — Laboratory research reconstructing evolutionary adaptations.
• 11:31-12:49 — Applying toxin resistance knowledge toward male contraception.

Episode Tone & Takeaways

Regina and Shab’s discussion is fast-paced, witty, and laced with tangible curiosity and fun—making complex evolutionary and biomedical science deeply accessible and human. The episode is a journey through nature’s chemical arms race, touching on medicine, art, genetics, and futuristic applications, all in under 15 minutes. If you’re a fan of nature’s weird solutions or ever wondered why Van Gogh’s stars glow so brightly, this episode is a must-listen.