In Our Time – "Pheromones" (Archive Episode)

BBC Radio 4 – Aired September 25, 2025
Host: Melvyn Bragg
Guests:

• Tristram Wyatt (Senior Research Fellow, Dept. of Zoology, University of Oxford)
• Jane Hurst (William Prescott Professor of Animal Science, University of Liverpool)
• Francis Ratnieks (Professor of Apiculture, University of Sussex)

Main Theme and Purpose

This episode of "In Our Time" delves into the world of pheromones: the invisible chemical signals that facilitate communication in the animal kingdom, orchestrating behaviors from mating and foraging to defense and social organization. The discussion spans from the historical discovery of pheromones in the 20th century to their evolutionary roles, applications in pest control, and the ongoing debate about their relevance in humans. The program emphasizes both scientific insight and moments of fascination, exploring how these subtle chemical cues underlie animal—and potentially human—behavior.

Key Discussion Points & Insights

1. Definition and Discovery of Pheromones

• Ancient and Early Observations: The concept of animals communicating by scent dates back to the Greeks and was noted by Darwin:
  • “During the season of love, a musky odor is emitted by the glands of the crocodile...” (Melvyn Bragg, 02:56)
• Chemical Isolation: Ernst Butenandt, using the bioassay of male silk moth wing fluttering, isolated and identified the first sex pheromone from half a million silk moths after 20 years of research (Melvyn Bragg, 04:36).
  • Memorable moment: The enormous effort required—half a million moths just for a few micrograms of compound.
• Electrophysiological Advances: Use of moth antennae as sensitive detectors predated the molecular identification—laying groundwork for modern approaches (Melvyn Bragg, 04:48–05:47).

Quote:
"It's invisible chemical signals between members of the same species." — Tristram Wyatt, succinct definition, (05:53)

2. Pheromones in Insects: Social Communication

• Social Insects as Model Systems: Honeybees and ants exemplify pheromone use to regulate complex group behaviors:
  • Foraging, reproduction, defense, and navigation all choreographed by specific pheromones (Francis Ratnieks, 06:08)
• Alarm Pheromone in Bees: Released when stung, smells like bananas, rapidly mobilizes hive defense (Francis Ratnieks, 07:46)
  • Advice: “Pull out the sting as fast as possible.” – Tristram Wyatt, (08:39)
    “It’s probably too late by then...” – Francis Ratnieks, (08:42)
• Ancient Recognition: References by Aristotle and Pliny the Elder, and early 17th-century British naturalists, show observational awareness pre-dating scientific explanation (Francis Ratnieks, 09:59).

3. Pheromones in Mammals: Simplicity and Complexity

• Stereotyped vs. Learned Behaviors: Mammalian brains introduce behavioral flexibility; simple responses are common in less learned situations, e.g., newborns (Jane Hurst, 11:07)
  • The rabbit mammary pheromone ensures that pups find their mother’s milk immediately—essential as mothers visit the nest for only minutes per day (Jane Hurst, 13:16).
  • This pheromone also induces learning, allowing pups to associate new cues with feeding.
• Mice and Maternal Odour: In contrast to rabbits, mice pups imprint specifically on their own mother’s unique scent (Jane Hurst, 26:11).

Quote:
"Newborn rabbit kits... start rapidly searching around with their noses and try to grasp hold of what essentially should be a nipple... it’s just stimulated by this very, very simple chemical." — Jane Hurst, (13:36)

4. Evolution of Pheromones

• Molecular Diversity: Pheromones range from simple volatiles to large soluble proteins, shaped by evolutionary pressures in various habitats (Tristram Wyatt, 15:28).
• From Cue to Signal: Example of goldfish—male response to hormones in water evolved into females emitting these molecules deliberately, becoming true pheromones (Melvyn Bragg, 16:30).
• Pheromones in Pest Control: Inspired by 19th-century observations, synthesized pheromones today disrupt mating in crop pests without affecting non-target species (Melvyn Bragg, 18:00–19:13).

5. Special Cases: The Queen Substance

• Honeybee Queen Substance: Studied before chemical structure known, regulates reproduction and social structure (Francis Ratnieks, 19:35)
• Royal Jelly as Allohormonal Pheromone: Ingested pheromones influence larval development, blurring lines between chemical communication and nutrition (Tristram Wyatt, 22:35).

6. Individual and Social Recognition in Mice: The Darsin Protein

• Scent Marking: Male mice mark territory with major urinary proteins (MUPs) as an individual signature.
• Discovery of Darsin: A specific, universally produced male mouse protein that’s potently attractive to females and triggers learning of individual male odors—named after ‘Darcy’ from Pride and Prejudice (Jane Hurst, 28:18–31:20).

Quote:
"A single male mouse in possession of Darsin must be in want of a mate." — Jane Hurst, (31:20)

7. Pheromone Perception and Adaptation

• Trail and Defense Pheromones in Ants: Ants lay complex pheromone trails, with short-lived and long-lived variants—even ‘no entry’ signals to guide colony activity (Francis Ratnieks, 33:35).
• Olfactory Systems: Many vertebrates use a special vomeronasal organ finely tuned for detecting single molecules—including pheromones (Jane Hurst, 35:17).
  • Humans lack a functional vomeronasal organ, unlike most other mammals.

8. Deception and Eavesdropping

• Deceptive Signals: Bolas spiders in North America mimic moth pheromones to lure and capture prey (Melvyn Bragg, 37:04).
  • Spiders modulate their pheromone mimicry according to the time of night to target different species.
• Predator-Prey Arms Race: Honeybees eavesdrop on predator hornet pheromones to trigger a ‘cooking’ defense, forming hot bee balls to kill invaders (Francis Ratnieks, 38:44–39:47).

9. Complex Responses to Pheromones

• Within and Between Sexes: Males and females, or individuals at different physiological states, respond differently to the same pheromone (Jane Hurst, 40:45–42:38).
  • E.g., the mouse protein Darsin attracts females but stimulates competitive countermarking and aggression in males.

10. Do Humans Have Pheromones?

• Scientific Uncertainty and Speculation: Many online pheromone products are pseudoscientific; credible research has yet to conclusively identify a human pheromone, particularly for sexual attraction (Melvyn Bragg, 42:51–44:09).
  • Possible exception: secretion from Montgomery glands around the nipple may elicit infant feeding responses in any baby.
• Challenges: Human sexual and social behavior is guided by cultural learning and individual choice, making discovery and study of stereotyped pheromone responses difficult (Jane Hurst, 44:28–45:32).

11. State of Research and Future Directions

• Advances in Chemistry: Modern instruments (gas chromatography, mass spectrometry) make identification vastly easier; early research required massive amounts of biological material (bonus: Francis Ratnieks, 46:20).
• Importance of Bioassays: Key to discovery is observing reliable behavioral responses under naturalistic conditions—especially difficult in humans due to ethics and immense behavioral variation.
• Definition Debates: Animal vs. human pheromone researchers diverge on what constitutes a pheromone, with animal researchers emphasizing robust, consistent effects.

Quote:
"If we test any of these pheromones on my mice, I can guarantee you they will respond... That’s the whole point about pheromones: it’s a reliable response..." — Jane Hurst, (50:17)

Notable Quotes & Memorable Moments

• On the enormous task of isolating the first pheromone:
  “Twenty years and half a million [moths]! ...staggering figures for someone to concentrate on something that seemed so elusive...” — Tristram Wyatt (04:36)
• On context dependence even in insects:
  “Context is everything... for example, turnip moth males turn off for 24 hours after mating... context-dependent.” — Melvyn Bragg (31:58)
• On quick learning in rabbit pups:
  “You see this very stereotyped response... essential for these pups to be able to feed efficiently.” — Jane Hurst (13:36)
• On human pheromone myths:
  “If you search for pheromones on the Internet, you'll get lots of sites offering [them] for sale... they're basically made up.” — Melvyn Bragg (42:51)

Timestamps for Key Segments

• Discovery of Pheromones & Definition: 02:56–05:53
• Pheromones in Social Insects: 06:08–10:58
• Mammalian Complexity (Rabbit Pheromone): 11:07–15:28
• Evolution & Applications (Pest Control): 15:28–19:35
• Queen Substance & Royal Jelly: 19:35–23:47
• Mice & Darsin Protein: 26:11–31:20
• Context & Ant Pheromones: 31:58–35:11
• Olfactory Systems (Vomeronasal Organ): 35:17–36:58
• Deception (Bolas Spider, Hornets & Bees): 37:04–39:47
• Sexual and Individual Variation in Responses: 40:45–42:38
• Human Pheromones Debate: 42:51–45:32
• Future Directions & Bioassays: 46:20–51:39

Conclusion

The episode intertwines scientific rigor and entertaining anecdotes, showcasing how pheromones underpin communication and behavior across the animal world. While insect pheromones are well-characterized and applied, mammalian and especially human pheromones remain an area full of mysteries and methodological challenges, with cultural and biological complexity fiercely at play. The show balances evolutionary history, mechanistic details, and the ongoing puzzle of our own chemical signals.

For further listening:
Next week’s episode will explore “Antara Ibn Shaddad and the poetry of the Arabian Peninsula before Islam.”

Produced by: Simon Tillotson, BBC Studios
Host: Melvyn Bragg