Radiolab: "Sperm Tales"

Date: October 7, 2008
Hosts: Jad Abumrad, Robert Krulwich
Guests: Joanna Ellington (fertility expert), Tim Birkhead (biologist, University of Sheffield), Harry Moore (sperm biologist)

Episode Overview

In this Radiolab "tidbit" episode, hosts Jad Abumrad and Robert Krulwich present a sneak preview of an upcoming full episode dedicated to the science, mystery, and mayhem of sperm. Through conversations with leading experts, the hosts explore the astonishingly complex, competitive, and occasionally cooperative world of sperm—dispelling myths and revealing bizarre true facts about human and animal reproduction. The tone is playful, curious, and often humorous as they journey from human sperm oddities to remarkable discoveries in the animal kingdom.

Key Discussion Points & Insights

1. Why Spend a Show on Sperm?

• [01:49] Robert frames the episode as a lighthearted but tantalizing teaser for an upcoming in-depth feature on sperm, noting, "Why would you spend so much time talking about that?" Jad adds, jokingly, "it's a very sad, sad, lonely show."
• The show promises unexpected insights from a deep dive into an ostensibly simple topic, living up to Radiolab’s trademark of finding fascination in small details.

2. How Many Sperm ‘Make the Cut’?

Interview with Joanna Ellington, Fertility Expert

• [02:22] Robert asks, if you’re “a healthy male at the top of your game... what proportion of your gang would be fit and ready to do the deed?”
• [02:50] Joanna reveals:
  • Only 14% (or more) of sperm are normally shaped in a healthy ejaculate; meaning 86% are abnormally shaped.

    "A normal ejaculate from a man is if you have 14—one-four—14% or more of the sperm that are normally shaped. That's a very low percent." (Joanna Ellington, 02:50)

• [03:06] Abnormal sperm may have:
  • Defective tails (can’t swim, go in circles, swim slowly)
  • Tails that are knotted or fail to unwind
  • Large, round "balloon head" (Globospermia)
  • Holes in the DNA (vacuoles)
  • Two tails, double or triple heads
  • Many are completely immobile (dead)

    "Some of them swim in a circle... some going slowly... some of them are going to be dead and not moving at all." (Joanna Ellington, 03:15-04:32)

• [04:36] Joanna summarizes that there are "hundreds of little enumerations that could go wrong" as sperm attempt to reach the egg:

  "If you were to actually write down everything that could go wrong with sperm... it would be hundreds of little enumerations..." (Joanna Ellington, 04:36)

Notable quote:

"But that's why men make sperm all the time. They constantly are making it. They constantly have a fresh supply." (Joanna Ellington, 04:43)

3. Sperm Competition vs. Sperm Cooperation

• Jad marvels at the odds, lamenting "the odds are not in our favor" [05:20]; Robert reinforces that this is “when you’re healthiest”.
• The public imagination (and pop culture) envisions sperm as competitors—racing to the prize.

  "The public image here is that every guy that you put in is, in a Woody Allen movie sense, competing against his neighbor." (Robert Krulwich, 05:36)

• But the hosts tease a twist: a surprising level of sperm cooperation in some animals.

4. Remarkable Sperm: The Wood Mouse Case

Story from Tim Birkhead (Biologist) and Harry Moore (Sperm Biologist)

• [05:58] Biologist Tim Birkhead and his colleague Harry Moore become curious after Moore’s cat brings in a wood mouse with "large testicles."

• [06:56] Examination reveals:

  • All rodents have sperm with slightly hooked heads, but the wood mouse’s hook is “extreme.”

    "The hook bends right back and touches the head again... it looked as though the hook was a specific adaptation to grasp the tails of other sperm." (Harry Moore, 06:56–07:15)

• [07:24] Experiment: Placing wood mouse sperm in special medium, Moore observes them forming “sperm trains,” gripping each other head to tail.

  "The sperm all joined up together in what he called sperm trains." (Harry Moore, 07:24) "It's a bit like spaghetti moving forward." (Harry Moore, 07:42)

• [07:45] Measurement shows these sperm trains move twice as fast as single sperm.

• Robert asks, if sperm cooperate, “Who gets to be the daddy sperm?”

• [08:08] Moore explains: Some sperm self-sacrifice (undergo the “acrosome reaction,” losing fertilization ability) to free others—allowing a “vanguard” to fertilize the egg.

  "They give up for their brethren." (Robert Krulwich, 08:21)
  "Yeah, that's exactly it." (Harry Moore, 08:24)

• [08:36] The sperm in a train are from the same male and share genetic interests, making sacrifice evolutionarily sensible.

  "All those sperm are related, so they all have more or less a common interest." (Harry Moore, 08:36)

5. Reflection & Teaser for Full Episode

• The hosts reflect on how surprising and “novel” it is to find sperm that cooperate rather than only compete.

  "The idea that a sperm would sacrifice itself for a brother sperm is very novel when you think about how normally this is thought of as such a competitive event." (Robert Krulwich, 08:50)

• They reiterate their excitement for listeners to hear the full episode in the coming weeks.
• Closing banter and plugging Radiolab’s website.

Memorable Moments & Quotes

• On sperm abnormalities:

  "Are there double headed ones?" (Robert Krulwich, 04:22)
  "Yes, absolutely." (Joanna Ellington, 04:23)

• On the competitive myth:

  "So it's Jerry versus Ted versus Andy versus Mark versus Freddy versus Billy and they're all rushing to the goal." (Robert Krulwich, 05:36)

• On sperm trains:

  "When he measured the speed at which the sperm trains moved, it was about twice that of isolated sperm." (Harry Moore, 07:45)
  "They all joined up together in what he called sperm trains." (Harry Moore, 07:24)

• On sperm sacrifice:

  "Some of the sperm undergo what's called the acrosome reaction... those sperm can no longer fertilise, but they free a vanguard of sperm that then can fertilize." (Harry Moore, 08:08)
  "They give up for their brethren." (Robert Krulwich, 08:21)

Important Timestamps

• 01:49: Introduction to the “sperm tidbit”
• 02:22–05:13: Discussion with Joanna Ellington about sperm morphology and fertility odds
• 05:36: Public image of sperm as competitors
• 05:58–06:56: Mouse sperm anecdote begins
• 07:24–08:24: Discovery and implications of “sperm trains” and cooperation in wood mice
• 08:36–09:15: Summing up—sperm cooperation and implications

Takeaway

This Radiolab episode teases the complexity and wonder of sperm biology, upending the classic narrative of ruthless individual competition with surprising tales of cooperation and sacrifice. Through clever storytelling and expert voices, the episode leaves listeners eager for the deeper dive to come.