Podcast Summary: "The Evolution Of The Butthole"

The Rest Is Science
Hosts: Professor Hannah Fry & Michael Stevens (Vsauce)
Release Date: February 12, 2026

Main Theme & Purpose

This episode of The Rest Is Science explores how asking playful scientific questions (like "How many holes does a straw have?") can lead to surprisingly deep insights about mathematics, evolutionary biology, and human anatomy—culminating in a lively, insightful discussion about how and why buttholes evolved. With their trademark wit and curiosity, Hannah Fry and Michael Stevens move from puzzled internet debates to big ideas about scientific progress, the limits of knowledge, and what makes humans unique.

Key Discussion Points & Insights

1. Mathematics Breaking & The Nature of Zero

Start: 00:26

• Listener Question: Why not invent math without zero, since division by zero "breaks" mathematics?
• Michael: "Shouldn't scientists busy themselves making a new math that doesn't have a zero?" (00:46)
• Hannah: Zero was a late addition to European mathematics; it came from Indian mathematicians via the Islamic world. It wasn't widely adopted in Britain until after Shakespeare's time. (02:50–03:28)
• Michael: The idea that "math breaks" at singularities (like dividing by zero or modeling black holes) is overstated—math is just a model, and sometimes its limits are exposed when reality behaves strangely. (03:28–04:25)

  "It feels so histrionic, like it's not breaking… it feels like clickbait." (03:28)

• Hannah: Physical equations are valid within certain scales or assumptions; they "break" when pushed beyond those domains (e.g., in singularities or black holes). Reality isn’t broken—the math just stops working. (04:25–07:19)
• Michael: Maybe we don't need new math, but a better understanding of what zero represents in reality. (08:19)
• Humorous aside: Pronouncing "Planck" as "Plonk."

  "From now on I'm going to call it Plonk's Constant, because I think that sounds much cuter." – Hannah (09:29)

2. The Fragility of Scientific Assumptions

Timestamps: 12:56–21:50

• Listener Question: What core assumptions might scientists be wrong about, and which would be most devastating?
• Hannah:
  • Dark matter is a big unknown—maybe it's not real; perhaps Einstein's theories break down at galaxy scales and we need "modified Newtonian dynamics" instead. (13:34–15:47)

    "There is this rival theory... which says, what if Einstein was just wrong?" (14:20)

  • The direction of time: We assume time only goes forward, but that's not always true in quantum physics. (16:00)
  • Constants of nature: Who says they've always had the same value everywhere and everywhen? (16:41)
  • Peer review: The process is assumed to guarantee true results, but is held together by "a lot of duct tape." (17:48)

    "Sometimes [selfish incentives] run counter to the things that serve that wide range." (19:02)

• Michael: Peer review is fallible, especially as AI makes it easier to "sound right" without being accurate. (20:33)

  "It's not God reviewed, it's peer reviewed." (18:20)

• Limits of Knowledge:
  • There may be things we're mathematically or fundamentally unable to know (e.g., consciousness).

    "We might discover that there are limits to what we can know that we don’t currently know about... left in the dark, having to accept it on faith." (20:33–21:39)

3. Human Obsession with Symmetry

Timestamps: 21:53–27:48

• Listener Jacob: Why do I feel compelled to center a poster? Is there an evolutionary basis? (21:53)
• Michael:
  • Humans evolved to value high-skill, difficult things—like making symmetrical tools or art—as markers of intelligence and fitness. (23:33)
  • Early stone axes were unnecessarily symmetrical, possibly for aesthetic or signalling reasons, not utility.

    "Humans that enjoyed things like, 'Hey, look this is symmetric,' did better... so now, we are their children."

• Hannah:
  • Right angles and symmetry are human inventions, rarely found in nature, but we surround ourselves with them.

    "Nature does not have right angles... but we are surrounded by them." (26:00)

  • The desire for symmetry is core to what it means to be human.

4. The "How Many Holes?" Debate: Topology, Straws, and the Human Body

Timestamps: 29:32–48:07

• Listener Question: How many holes does a straw have?
  • Michael: Topologically, a straw has one hole. If you stretch it, it’s like a plate with one hole. (29:48–30:54)

    "By using a mathematical definition of a hole, the straw has one." (30:19)

  • Hannah: Topological debates depend on whether you count "boundaries" (ends of a straw) or "tunnels" (the through-hole). Both sides of the argument make sense, but the formal mathematical approach gives a clear answer. (31:09–35:01)
• Topology & Early Life:
  • Early animals (e.g., jellyfish) only had one opening, used for both eating and excreting—an inefficient system.
  • Evolution's big leap: forming a through-gut (two openings/tunnel)—the origin of the anus. (37:09)

    "Around about 550 million years ago...a worm-like creature...evolved a second hole—a tunnel all the way through." (37:38)

  • This innovation ("the butthole revolution") enabled more efficient digestion and complexity in life forms. (38:03)

    "The butthole as an innovation was genius." – Hannah (38:07)

• Human Anatomy as Topology:
  • Humans (like most animals) are essentially a donut: a tube with a hole running through from mouth to anus.
  • Our mouths, noses, and eyes are clustered at one "end" of the tube for efficient food sensing and intake.
  • There’s a crucial anatomical crossover in the throat between the breathing and food tubes—necessary for brain and body integration, but also the reason choking is a risk. (39:53–41:53)
• Michael’s Viral Video: "How many holes does a human have?" (42:43–45:56)
  • Definition: Holes must be big enough for a human hair (≥ 60 microns). By this, humans have seven holes:
    1. Mouth-to-anus (digestive tract)
    2. Left nostril
    3. Right nostril
    4. Left eye lacrimal punctum (tear duct)
    5. Right eye lacrimal punctum
    6. Left eye (second tear duct)
    7. Right eye (second tear duct)
    • Ears don’t count; tympanic membrane blocks passage. (43:19–43:56)
  • Hannah: Received a wood-turned model representing this topology—a "seven-holed" human. (44:25–46:28)

    "Just that. Really loving right angles as well. This is us... The whole description of humanity that you ever need." – Hannah (46:28)

  • Piercings, Anomalies: More holes can exist with piercings or rare anatomical variations. (47:15–47:42)

Notable Quotes & Memorable Moments

• Hannah on the butthole’s evolutionary impact:

  "Pooping and eating out of the same hole is not a good idea, I would say." (37:04)
  "The butthole as an innovation was genius." (38:07)

• Michael, humorously abstract:

  "[Eating on the toilet] is a celebration of the fundamental donutness of my body." (38:43)

• On limits of knowledge:

  "I think we might discover that there are limits to what we can know... We’ll be left in the dark, having to accept it on faith." – Michael (20:33)

• On symmetry and right angles:

  "Nature does not have right angles... but we are surrounded by them." – Hannah (26:01)

Important Timestamps

• [00:26] – Introduction of listener question about "zero" in mathematics
• [03:28] – Zero’s slow adoption in Europe
• [07:19] – Mathematical equations "breaking" vs. limits of models
• [13:28] – Core scientific assumptions and dark matter
• [17:48] – Assumptions in scientific publishing and peer review
• [21:53] – Why we crave symmetry (poster-centering)
• [29:32] – The "how many holes in a straw?" debate
• [37:38] – The evolutionary innovation of the butthole
• [43:19] – Human body: how many holes?
• [44:25] – Hannah’s wood-turned "seven-holed" human
• [47:03] – Variations, anomalies, and piercings: more holes possible

Tone & Language

The conversation’s tone remains witty, playful, and highly accessible—balancing deep scientific explanation with approachable humor and good-natured banter. The hosts’ chemistry keeps the episode lively and relatable, no matter how weird the questions get.

Episode Takeaways

• Even silly questions (e.g., "how many holes?") can reveal profound insights about evolution, anatomy, mathematics, and human behavior.
• The evolution of the through-gut (butthole) was transformative, enabling complex animal life.
• Symmetry and right angles are unnatural, but distinctly human obsessions—reflections of our cognitive and evolutionary lineage.
• Scientific models have limits; progress requires questioning even the most foundational assumptions.
• Topology offers a mind-bending but practical way to understand ourselves—humans, at heart, are just fancy, symmetrical tubes.

For more quirky science questions and brainy fun, tune in weekly to The Rest Is Science.