Radiolab — "Kleptotherms"

Date: February 6, 2026
Hosts: Lulu Miller & Latif Nasser
Theme: The deep ties between warmth—physical, emotional, and social—and our lives, exploring how creatures (including humans) "steal" heat, what warmth means for those on the edges, and why our most trusted number in health may be more myth than fact.

Episode Overview

This episode of Radiolab takes listeners on an imaginative and investigative journey into the notion of warmth—how organisms seek, share, and sometimes "steal" it in surprising ways. Starting with the natural phenomenon of kleptothermy (the act of stealing heat from others), the show unspools stories that wander from the animal kingdom to human experiences of mental illness, social isolation, and the way body temperature became a cultural touchstone. Throughout, Miller, Nasser, and their guests probe at where the line between biological need and social signal begins to blur, leaving listeners with a new sense of how temperature is woven through both body and mind.

1. Kleptothermy: The Art of Stealing Heat

[01:13–06:30]

Key Points

• Lulu Miller invites listeners on a whimsical “storybook” journey, introducing the concept of kleptothermy—obtaining heat from another creature ("engaging in heat theft").
• Hans Isermann, a social scientist at University Grenoble Alps, shares examples from the animal kingdom:
  • The blue and black amphibious sea snake of New Caledonia sneaks into seabird burrows to "hug" birds, absorbing their heat without eating them.
    • “[The snakes] take advantage of the mass body heat in warming their own bodies.” (Hans Isermann, 03:43)
  • Male garter snakes pretend to be female to stimulate mating attempts from other males, gaining warmth through friction.
  • Dwarf caimans lie on termite nests to absorb collective bug heat.
• Humans also "steal" heat through huddling/cuddling—an act that, in scientific terms, is at least partially theft.
• Biologists see this as part of the “economy of action”—using less energy by sharing warmth is more efficient than creating it on one’s own.
  • “Getting our warmth from another creature is super efficient. It can decrease the cost of thermoregulation by up to about 60 or 70%.” (Hans Isermann, 05:29)
• Our sensations of warmth are deeply social and communal, a bond that shaped how we survived winters.

2. Redundant Clothing: Schizophrenia, Warmth, and Isolation

[06:51–22:22]

Key Points

• The story of John, a man from Connecticut, tracks his struggles with weight, mental illness, and experiences of cold:
  • As John’s mental illness (schizoaffective disorder, later paranoid schizophrenia) becomes more severe, he begins wearing excessive layers—even in summer.
    • “I think it's a way of shielding myself from the world...I was just doing what felt natural.” (John, 13:56)
  • He observes social judgment—others fear or shun him when they see his unusual attire.
• Multiple psychiatrists (in India, Australia, the US) notice the same "redundant clothing" behavior in patients with schizophrenia.
  • Dr. Tathagata Mahintamani's studies find that patients wearing layers have lower T3 and T4 thyroid hormone levels, markers linked to temperature regulation:
    • “With cold intolerance, like, you just get cold quicker.” (Dr. Mahintamani, 15:08)
  • Suggests that the need for layers may be due to actual physiological coldness—not just confusion, erraticism, or lack of motivation.
• Non-treatment, or "going it alone," in schizophrenia appears correlated with the redundant clothing signal. Dr. Mahintamani muses that this may be a visible "cry for help."
  • “This kind of redundant clothing might be a window through which we can peep towards something really, really broken down.” (Dr. Mahintamani, 19:35)
• One poignant story details how a stranger's simple kindness (“Don’t feed the birds, just eat your food”) helps John relax enough to finally peel away his layers and touch the sand—his first moment of ease.

3. Rejection Hurts—And Makes You Cold

[22:59–24:45]

Key Points

• Hans Isermann describes Cyberball, a psychology experiment in which participants are excluded from a ball-tossing game. In the exclusion condition:
  • People not only rate the room as colder but actually experience a measurable drop in skin temperature.
    • “It was stunning to find it...it also opened up the door for figuring out what else was there.” (Hans Isermann, 24:15)
• The bridge between emotional and literal cold/heat is established—social warmth and ostracism can literally alter bodily temperature.

4. Body Temperature: The Myth and Meaning of 98.6

[24:53–37:41]

Key Points

• The COVID-19 pandemic made the act of taking body temperature—a “literal passport back into society.”
• Their crowdsourced temperature recordings reveal huge variance among “normal” people.
• The origin of 98.6°F is traced back to 19th-century German physician Carl Wunderlich:
  • Wunderlich’s data, later publicized/marketed by Edward Seguin and thermometer companies, burned the number into medical and cultural consciousness.
  • In reality, Wunderlich’s “average” was a statistical artifact, and his methods/focus differed from modern science.
  • “98.6—that thing we all sort of bow before—was just a little footnote from the 1800s.” (Lulu Miller, 32:03)
• Modern research (Katherine Ley, Stanford) shows:
  • No such thing as a fixed “healthy” temperature.
  • Women have higher temps than men; the young higher than the old; height, weight, time of day, hormones, and even location all matter.
  • Recent studies show that our average temperature is now closer to 97.5°F and is dropping over decades.
  • “For some people, because you’re a man, you’re old, and it’s early in the morning, coming up to 98.6 might actually be a fever for you.” (Deanna Day, 35:41)
• Despite this, people (including the hosts) still reflexively judge health or illness based on this old standard.

Memorable Moment

• Lulu, sick after a COVID shot, takes her temperature:
  • “I think my fever must be like 102...and it just comes out as 98.1. Am I a big faker?...The thermometer just said I wasn't sick.” (Lulu Miller, 36:36)

5. The Social Life of Temperature: Networks, Emotions, and the Body

[37:57–41:25]

Key Points

• Hans Isermann’s research finds that the diversity of a person’s social network is a key predictor of their core body temperature—more types of social groups often means a higher baseline body temp.
  • Suggests our bodies register the safety of our social connections.
  • “The more kinds of groups you had, the higher your core body temperature was...” (Lulu Miller, 39:30)
• Emotional experience—loneliness, exclusion, connection—profoundly impacts our biological warmth.
• The closing montage reframes every temperature check as a possible window into a web of biological, emotional, and social truths:
  • “Did you talk to your sister? Are you on medicine? Or maybe you're off it? Do you live alone? Who do you love? Have you seen them?” (Lulu Miller, 40:47)

Memorable Quotes

• “There’s just something so primal about the heat being more important even than the meat.”
  —Lulu Miller, [03:56]

• “Getting our warmth from another creature is super efficient. It can decrease the cost of thermoregulation by up to about 60 or 70%.”
  —Hans Isermann, [05:29]

• “I think it’s a way of shielding myself from the world...I was just doing what felt natural.”
  —John, [13:56]

• “With cold intolerance, like, you just get cold quicker.”
  —Dr. Mahintamani, [15:08]

• "This kind of redundant clothing might be a window through which we can peep towards something really, really broken down."
  —Dr. Mahintamani, [19:35]

• “98.6—that thing we all sort of bow before—was just a little footnote from the 1800s.”
  —Lulu Miller, [32:03]

• “For some people...coming up to 98.6 might actually be a fever for you. This is exactly why it’s important to not believe that a number like your temperature can tell you everything.”
  —Deanna Day, [35:41]

• **“The more kinds of groups you had, the higher your core body temperature was, the more kind.” —Lulu Miller, [39:30]

Segment Timestamps

• [01:13–06:30] — Animal kingdom kleptothermy
• [06:51–22:22] — Human “kleptothermy”: Schizophrenia, layers, and warmth
• [22:59–24:45] — Social rejection and literal coldness (Cyberball experiment)
• [24:53–37:41] — The legend of 98.6°F: History, myth, and new science
• [37:57–41:25] — Social networks, emotion, and the biology of warmth

Episode Takeaways

Radiolab’s "Kleptotherms" explores not just how heat moves from body to body, but how our biological drives for warmth inform, and are informed by, both our mental lives and social worlds. From evolutionary strategies to hidden signals of distress, from 19th-century big data to the pandemic’s temperature guns, the show peels back the myth of objective temperature—revealing it as a rich, shifting window into animal cunning, human loneliness, community, and care.

Recommended for listeners curious about: The intersection of biology, society, and emotion; mental health; the cultural construction of “normal”; why warmth is never just physical.