Dr. Jonathan Reisman on the Unseen Body: Throats, Hearts, Poop, Sperm and Medicine at the Ends of the Earth

High-Level Overview

Lex Fridman talks with Dr. Jonathan Reisman, an emergency room physician trained in both pediatrics and internal medicine and author of The Unseen Body, a book that explores the hidden, messy and fascinating details of human anatomy. Reisman has practiced medicine in some of the world's most remote places, including the Alaskan and Russian Arctic, Antarctica, the Himalayas of Nepal, Calcutta, the Pine Ridge Reservation and Appalachia. The conversation roams organ by organ, from the hand and the throat to the heart, blood, genitals, feces, sperm and liver, and then outward to Arctic diets, war and medicine, ship doctoring in Antarctica, artificial organs, the humbling history of medicine, and the meaning of life.

The tone is playful, curious and frank. Reisman clearly relishes the gross parts of the body and treats them with the same fascination as the elegant ones, while Lex leans into jokes about humans being "a bunch of holes" and a fancy tube, then turns philosophical about death and why we ask why. The discussion moves from evolutionary design and taboos to the raw humanity of the emergency room, travel stories from Kamchatka and Barrow, a tribute to Paul Farmer, advice for young people, and honest reflections on suicide and mortality.

The Discussion Explores:

• Which parts of the body are brilliant designs (the hand) and which seem flawed (the throat)
• How millions of years of sex and death shaped the human body, and why our most universal functions are the most taboo
• The first day of anatomy lab, and what a body reveals about the life it lived
• The heart as a simple pump, blood as a crystal ball, and the body's weak points for infection
• Genitals, menstruation, testicles, artificial wombs, diarrhea as a clever microbial strategy, and sperm
• The liver, organ transplants, and Arctic diets built on raw fat
• War, Antarctica, Mars, and why every doctor may one day look like a quack
• Paul Farmer, following your passion, suicide, death, and the question of why

Deep Dive into Main Ideas

Feature or Bug? The Hand and the Throat

Lex opens by asking whether the body's parts are optimal solutions or duct tape. Reisman thinks most are the best available solution, and holds up the hand as a marvel: muscles sit in the forearm and tendons run down "like strings on a puppet," giving the dexterity to do everything from gripping to playing piano. Surgeons will go further to save a thumb than a pinky tip because the thumb is so crucial to work and self-care, and two hands matter for spearing, shooting a bow or butchering an animal.

The throat is the opposite. The paths for food and air come within millimeters of each other, so if you laugh while eating or speak while swallowing, "you die from choking." In med school, when every other system seemed brilliantly designed, the throat "seemed set up almost for failure." The body compensates with a gag reflex, the cough, a "mucus elevator" that constantly carries debris up from the lungs to be swallowed, and a swallowing act coordinated by several cranial nerves and more than 15 muscles, lifting the airway against the epiglottis. Even whales have the same problem, with a recently discovered organ to help keep food out of their airway. The root cause is embryonic: we begin as a tiny disc that rolls into a tube, and each end of the tube splits into the openings we have.

Sex, Death and Taboo

Reisman once tweeted that "millions of years of sex and death" designed the human body. Sex is how genes get passed on and death weeds out the gene pool, so who reproduced before dying a million years ago shaped what we look like now. He expects any alien civilization to depend on the same forces. Lex extends the idea to wisdom and adaptability, suggesting death is how nature clears out stubborn old ideas.

What Reisman finds strangest is that the body's most universal functions, what we do in the bathroom and the bedroom, are the most taboo. Some taboos vary by culture; among traditional Iñupiat, he notes, parents having sex in front of children was normal in winter quarters. Others serve public health, like the Indian taboo on the left hand, which is used for wiping, creating a social asymmetry on a symmetrical body. As for awe, he names the brain but calls the kidneys "the unsung hero of the body," constantly adjusting the bloodstream and consuming huge amounts of energy. He nearly became a kidney specialist but couldn't pick just one organ, which is why he is a generalist.

The Cadaver and the Stories Bodies Tell

On the first day of medical school, Reisman's class began dissecting cadavers, starting with the superficial muscles of the back. He was so fascinated by this behind-the-scenes look at how bodies move that he decided, before the end of that first day, to donate his own body to science, and he is sticking with it. Students never learn a cadaver's name, but the body reveals a lot: his was a smoker with coronary artery disease, and others had metal joints or a surgically removed kidney. Scars are "a story written in the language of scar," and in the ER he reads surgical scars to rule diagnoses in or out; if the appendix is gone, abdominal pain is not appendicitis.

Some classmates had nightmares at first, but everyone adjusted, which taught him how much people can get used to, from war to oppression. He believes medical training can leave psychological scars, though the first cadaver is rarely the worst of it. Asked about the future, he sees huge untapped potential in the data from smartwatches and genetics to predict drug reactions, and notes that Moderna made its COVID vaccine without ever having the virus in its lab. On Elizabeth Holmes and Theranos, he says the goal of running many tests on a drop of blood was genuinely worthy, comparable to finding non-addictive painkillers as strong as opioids, and notes pediatric medicine already gets similar information from tiny tubes.

The Heart, Blood and the Body's Weak Points

Reisman admits that when he was smitten with a fellow medical student he felt a burning in his chest, possibly acid reflux from nerves, so he understands why people link the heart to love. But the heart is "just a simple mechanical pump" that fills and squeezes, creating the pressure to reach every cell, including the brain when we stand. Each red blood cell circulates in about five minutes, and blood serves as "the fresh water and the sewage system in one," delivering oxygen and nutrients and removing waste. For doctors, blood is "like this crystal ball," revealing the health of the liver, heart and kidneys. In the U.S., cardiovascular disease is among the most common causes of death today, though a century or two ago infections killed more people.

Asked how he would attack the body if he were a pathogen, Reisman points to its unavoidable weak points: we must breathe and we must eat, which is why respiratory and gastrointestinal infections are the most common. He would choose a deep pneumonia that crosses into the blood rather than "a lazy cold in the nose."

Genitals, Menstruation and Artificial Wombs

Unlike other organs, which keep us alive moment to moment, genitals are not needed at all for survival and "often make us do stupid things." Their purpose is genetic variety through mixing. Reisman finds the uterus remarkable: girls are born with all their eggs, yet menstruation does not begin until the second decade of life, and it runs on a slow monthly rhythm. When the heart or breathing rhythms stop, it is an emergency; when menstruation stops because of pregnancy, that is the whole point. Lex suggests the delay lets the brain develop before making mating decisions, and Reisman adds that a child's body simply isn't big enough to carry a pregnancy.

As a redesign, he would like testicles kept safely inside the body, which would require sperm production that works at body temperature rather than a few degrees cooler. He notes some baleen whales have penis-like erectile tissue in their mouths to shed heat. He is excited by artificial wombs, which in animal studies have extended gestation by about a month and could spare premature babies lifelong organ and brain damage. Some organs can be offloaded to machines, like kidneys through dialysis, but there is no dialysis equivalent for the liver.

Poop, the ER and the Great Equalizer

Poop, Reisman says, is "hilarious, and also dangerous: gastrointestinal infections spread by the fecal oral route. Diarrhea is a brilliant strategy for microbes, tricking the gut into flooding itself so the pathogen reaches the water supply and new hosts, just as respiratory viruses trigger coughing. In the ER he becomes a poop detective," asking a sweet grandmother about color, consistency and whether it floats, which requires a special blend of intimacy and professionalism.

The ER, he says, shows humanity at its most raw: psychiatric emergencies, overdoses, suicide attempts and abused children all come there, making it the catch-all for what people do to themselves and each other. Yet humans get used to anything, and doctors can treat a heart attack or a baby half-delivered as routine. Writing helps him keep his fascination. He quotes the spirit of Chekhov, who treated both peasants and aristocrats and observed that underneath, everyone has the same failing bodies and the same worries. Lex reads Reisman's poem about a medical student whose white coat starts as a costume and whose rehearsed act slowly fades into a profession, until you "suddenly find yourself unable to tell if you're still acting."

Sperm and the Liver

Lex cites Reisman's tweet that the average man produces about 500 billion sperm, four to five times the number of people who have ever lived, each genetically unique. Reisman calls sperm the body's only normally projectile fluid, compares ejaculation to a touch-me-not flower launching seeds, and notes sperm are fueled by fructose, "food for the journey." He finds it astounding how often reproduction works despite everything that can go wrong, concluding that people simply have a lot of sex, so statistics favor success. Lex notes research suggesting the winner is not necessarily the fastest sperm.

The liver is "like 15 organs in one": it receives all blood from the gut first, acting as gatekeeper for what we absorb, detoxifies and metabolizes substances like alcohol and Tylenol, packages cholesterol and fats, makes clotting factors and processes bilirubin. Echoing the myth of Prometheus, it genuinely regenerates when parts are removed. Kidneys are the easiest organ to transplant because living donors have two and they are small enough to tuck into the pelvis; mechanical heart-assist devices have advanced so quickly that transplants may become less necessary. An Instagram post of cooked bull testicles prompts his note that eating them won't boost libido, because the liver metabolizes swallowed testosterone before it reaches the bloodstream.

Blubber, Kamchatka and a Life of Travel

Reisman loves the traditional diets of the far north, where more than half of Iñupiat calories once came from marine mammal and other fat. He has eaten raw whale blubber (maktak), beluga chowder, and whale meat fermented in whale blood, and describes a lawn covered in whale blubber as the Arctic equivalent of a plush suburban lawn. With little fuel for fires, much food is eaten raw; one half-Iñupiat man proves his heritage by biting the head off a raw bird. He once spent 45 minutes studying a bowhead whale's heart the size of a yoga ball. As a doctor, he says, he knew fat as the villain of the obesity epidemic, but in the Arctic, fat has always meant health and survival.

His travel bug began after NYU, when he spent six months in St. Petersburg researching how environmental groups pushed Russia's timber industry toward sustainability, a niche that became a window into the whole country. He learned Russian from a babushka who also taught him to ride a horse, and he found elderly Russian women, including a blind Koryak woman who loved Dostoevsky and Tolstoy, profoundly wise. In remote Kamchatka villages he was struck by how similar the family politics were to New Jersey suburbs. He fashioned a medical career around interesting places where care is needed, and calls Russia's scientific potential unrealized; on the war in Ukraine, he calls it tragic and seemingly pointless.

War, Antarctica, Mars and Medical Humility

Reisman says it has been said that war is the best medical school: Iraq and Afghanistan changed civilian trauma care through tourniquets, whole blood transfusions and battlefield pain control like ketamine and fentanyl lollipops, and DARPA funds moonshot research. Infection has historically been as big a wartime killer as trauma; his grandmother caught typhus in World War II. Contrasting Shackleton's tiny kit of paregoric and laxatives with his own cabinets of drugs and an EKG machine as a ship doctor in Antarctica in 2018, he notes that far from hospitals, a brain bleed simply kills you. Australia reportedly removed healthy gallbladders before Antarctic postings, and Mars colonists might need appendectomies and heart screening. With a wife and two small children, he wouldn't go to Mars himself, though he sees space as an extreme extension of the high-altitude medicine he has practiced in Nepal.

His tweet that from far enough in the future every doctor today will look like "a total quack leads to a sober look at medical history. Doctors bled George Washington to death while he had a peritonsillar abscess, and a saying holds that half of what you learn in med school is wrong by the time you finish. Sham surgery trials suggest knee arthroscopy and stents for stable chest pain may not beat placebo, even though both seemed obviously effective. Lex argues future medicine will rely on vast personal data and AI, and that today's practice is very 19th century"; Reisman stresses that humility is essential because dogma has been thrown out so many times.

Paul Farmer, Passion and the Question of Why

Reisman calls the late Paul Farmer, founder of Partners In Health, a zealot for bringing care to the world's poorest people, and recommends Tracy Kidder's book about him, Mountains Beyond Mountains. In places like Calcutta, he says, children still die of diarrhea and pneumonia that pennies' worth of oral rehydration or amoxicillin could treat. His advice to young people is to find a passion and follow it wherever it leads without needing a detailed plan; his defining moment was lying on a hard floor in a Kamchatka hunter's cabin, overwhelmed with gratitude. He loves medicine as detective work, handwork and teaching, and says experienced clinicians develop a sense that a patient "just doesn't look good" that no lab value captures.

On darker topics, his two big adult realizations are that no one knows what they're doing and that suicide is incredibly common, often rooted in trauma that leaves lasting scars; he urges people to keep fighting, and Lex tells listeners who are struggling that "we're in this together." Watching patients die taught Reisman that much of death's horror falls on those left behind, and having kids changed how he thinks about his own. Asked the meaning of life, he suspects "why may be a trick of the human brain, perhaps an evolutionary adaptation from asking practical questions while hunting and gathering, which we now extend to unanswerable ones. Lex closes with Paul Farmer's words that the idea that some lives matter less is the root of all that is wrong with the world."

Conclusion

Jonathan Reisman offers a tour of the body that is funny, frank and full of wonder, showing that even its most taboo or unglamorous parts, from mucus and poop to the uncelebrated kidneys and liver, are remarkable pieces of evolutionary engineering, flaws and all. His stories from the Arctic, Antarctica and the ER reveal medicine as both science and deeply human work, a great equalizer where everyone's body fails in similar ways. Running through the conversation is humility: about how much medicine still gets wrong, how unevenly its benefits are shared, and how little we understand about death and meaning. It is an episode that will leave listeners more curious about their own bodies and more appreciative of the doctors who care for them.

This is a summary of "#297 – Jonathan Reisman: The Human Body – From Sex & Sperm to Hands & Heart" from Lex Fridman Podcast, giving you the GIST so you can decide if you want the REST. Listen to the full episode.