Two Tubes, Millimeters Apart: Jonathan Reisman on the Honest Design of the Human Body

Lex Fridman opens with the question Reisman's book is built to answer: from an evolutionary perspective, is the human body a feature or a bug? Reisman, an emergency and pediatrics physician who has practiced in the Alaskan and Russian Arctic, Antarctica, and the Himalayan mountains of Nepal, says most of the time the way the body works is the best solution he has seen. He has not been shown many alternatives. Some parts, though, make more sense than others.

The hand is the exhibit he keeps returning to. Muscles live up in the forearm; tendons run down like strings on a puppet, and the result is a dexterity he finds hard to improve on, whether you are holding a tool, playing piano, or doing surgery. Injuries make the ranking obvious. He tells the story of a man whose thumb was nearly ripped off by a dog leash. Plastic and orthopedic surgeons will debate how much of a finger is worth saving. They will go further, with more operations and more aggressive therapy, for a thumb than for the tip of a pinky, because the thumb is what occupation and self-care actually run on.

Two hands, he thinks, are not just the symmetry nature likes to print. A one-handed hunter would be a much less formidable survivor: spearing, drawing a bow, butchering an animal all want a second grip. Three hands is a question he is happy to leave unanswerable. The throat, by contrast, looks like a duct-tape job. Food, drink, saliva, and mucus must go down the esophagus; air must go down the trachea, millimeters away. Slip once — laugh while eating, speak while swallowing — and you can die of choking. He is not sure it could have been arranged any other way, given that we form in the womb as a tiny tube. It is still, he says, an unfortunate thing.

Fridman reads a Reisman tweet as if it were verse: millions of years of sex and death designed the human body. Reisman does not treat it as a flourish. Sex is how more of us get made; death is how the gene pool gets weeded. Whether you die before you reproduce is a large part of who survives. Who lived and who died before reproductive age a million years ago, he says, is pretty important in what we look like now. Who has sex and who dies now may still shape the body a million years on, unless technology takes a bigger role than biology.

Would an alien civilization of similar or greater intelligence still need something like sex and something like death? Reisman would guess yes. It seems to be required on Earth, and any system that has to adapt to a changing environment needs variation and a way to clear the stubborn old ideas. Fridman pushes the immortality problem: wisdom is experience solidified, and solidification is exactly what stops you reinventing yourself. Death does that ugly work of forced re-adaptation. You could imagine one immortal mind with two modes, teenager in the morning and elder at night. Reisman does not claim to know the distant future. He does think the dependence on who reproduces and who dies is foundational.

Asked for the weirdest thing about the body, he does not pick an organ. He picks a social fact: the most universal acts are the most taboo. What we do in the bathroom, in the bedroom, to our own genitals, is what we hide, even though it is the thing we all have in common. Societies love rules about public versus private. In traditional Inupiat communities, parents having sex in front of children was ordinary; going outside in an Arctic winter was not an option. In India the hands are anatomically symmetric, but culture makes the left hand the dirty one used for the toilet and the right hand the one for eating and greeting. The public-health root made sense, he says. You should not shake hands with the hand you just used to clean yourself. Once soap exists, the taboo still hangs on, because society changes slower than technology.

The Unseen Body starts with the throat because Reisman wanted to throw the reader into death the way medical school threw him. On the first day of anatomy lab his cadaver lay face-down on a metal gurney. They pulled back the plastic sheets, cut the skin of the back, and dissected the latissimus dorsi. They did not enter the chest or abdomen. Before the day was over he had decided to donate his own body for the same purpose, and he has not changed his mind. A future student might listen to this podcast while taking him apart and never know. Cadavres do not come with names or listening histories. They come with evidence.

His own cadaver was a smoker with coronary artery disease and extra weight. Other bodies in the lab had metal joints, or a kidney missing in a way that said surgical removal, likely a tumor. Skin is a language of scar. He still has a large cut on his hand from age thirteen, and every glance recalls the incident. Deer hides carry marks that look like barbed wire, or like an antler from a fight. In the emergency room those marks become data. Abdominal scars tell him a gallbladder, an appendix, or a uterus is already gone. No appendix, no appendicitis. The footprints of past surgeries shrink the differential before a single lab comes back.

Classmates had nightmares in the first weeks; then, as far as he knows, everyone got used to it. That was a larger lesson than anatomy. People can get used to almost anything, including war and life under oppressive regimes. Some of those early shocks leave marks the way a fence leaves a scar. One student who had nightmares became a surgeon and now looks inside bodies all day. The first cadaver, he thinks, is rarely the most traumatic thing a doctor will see.

Fridman asks about richer data in a digital age, and about Elizabeth Holmes. Reisman thinks wearables already collect more than medicine knows how to use, and that genetics will eventually tell you which drug you will tolerate. Moderna's COVID vaccine, he notes, was designed from a genome without the virus ever being in the lab. Theranos aimed at a worthy frontier: less blood, more information, maybe a device at home. He trained in pediatrics and internal medicine and still does not understand why adults cannot be drawn with the tiny tubes used on children. If Theranos had actually done it, it would have revolutionized practice. The goal, he says, sits next to a non-addictive opioid as a genuine medical moonshot. The failure was the gap between the promise and the work.

Fridman's friend sees people as a bunch of walking holes. Reisman tightens the joke. More accurately, we are a tube. In the womb we start as a microscopic disc, almost a flatbread, then roll in like a burrito. The tube grows. Each end splits. Up front you get nose, mouth, ears, sinuses, windpipe, esophagus. At the other end, men end up with two holes and women with three. "We sprout eyes and a brain and a sense of smell and taste pretty much to regulate what comes in the front of the tube." Respiratory and gastrointestinal infections are the most common for the same reason: those are the ways in. Smell and taste are the checkpoint. The rest of the organs, he will argue later, keep that tube running. Genitals are the exception.

The throat's problem is that it is too multifunctional. The pancreas is two organs in one; the liver is like fifteen. The throat has to keep everything but air out of the windpipe, and the two paths come within millimeters. Compensation stacked on compensation. A gag reflex rejects food headed the wrong way. A cough flushes what got through. A mucus elevator, a constant upward flow of mucus, drags inhaled particles and stray food back to the throat, where we swallow it all day without noticing. Swallowing itself uses more than fifteen muscles and several cranial nerves. You can watch the Adam's apple jump as it lifts the airway against the epiglottis so the swallow can skirt past. Every sip is that close.

Someone asked him whether any animal designed the throat better. Whales were his first thought, with the blowhole on top of the head. He looked it up. The paths still come very close; a recently noticed organ helps keep food out of the airway. Tubes remain tubes. At the microscopic level, how ions rush in and out of nerve cells to coordinate the swallow is still full of mystery. The act itself is thankfully thoughtless. If we had to think about it, we would think about it all day.

Poetry loaded the heart with love and life. Reisman, who as a lovesick medical student felt a burn in his chest he still cannot diagnose, says the organ is a simple mechanical pump. Once animals got thick enough that inner cells lost contact with the nutritious brew around them, something had to distribute nutrients. The heart fills and squeezes, creating the pressure that feeds every cell, especially a brain at the top of an upright body. Every red blood cell is said to loop back in about five minutes. Circulation starts in the womb and does not get a break until death. Blood is the freshwater and the sewage in one, and for a doctor it is a crystal ball: liver, heart, and kidney can all be read from a sample. If Reisman were a parasite looking for a way in, he would pick the respiratory or gastrointestinal tract, because we have to breathe and eat. That is why those infections dominate. Sex is another door.

Genitals, he likes to point out, are the opposite of every other organ. Heart, lung, kidney, and liver cannot stop. You do not need genitals from moment to moment. You do not have to use them at all. They often make people do stupid things that work against survival. The uterus is strange even among them: it does not wake up until the second decade, though female babies are born with all the eggs they will ever have. Menstruation is a slow rhythm, once a month, after a decade of silence. When other body rhythms stop, that is an emergency: cardiac arrest, apnea. When menstruation stops because of pregnancy, that is the point of the whole apparatus.

Asked how he would improve the penis and vagina, he starts with the testicles. They begin in the abdomen and descend, sometimes never, because spermatogenesis works a few degrees cooler than body temperature. In heat they hang farther down; in cold they scrunch up. A sperm-making chemistry that ran at body temperature would let them stay inside, protected like ovaries. The penis, he says, is pretty good as it is. Some baleen whales even have similar erectile tissue in the mouth to dump heat through all that blubber. For the uterus he would want more protection from infection and trauma. Artificial wombs, already prolonging animal gestation, look to him like a heart-lung bypass for a fetus, and a possible answer when premature labor cannot be stopped. Kidneys can be replaced by dialysis for decades. The liver has no such substitute. Fail it, and you need a transplant.

Poop is the most hated product of the body, and with reason: gastrointestinal infections travel the fecal-oral route. Reisman describes diarrhea as a brilliant microbial trick. If you are a microbe in one person's gut and your goal is another person's gut, you induce the intestine to dump fluid, raise volume and runniness, contaminate the water, and infect everyone downstream. Tuberculosis and coronavirus do the same trick with a cough. Fridman underlines the lesson: diarrhea is intelligent, not as a thought in a human head, but as an accomplishment of the whole system of bacteria, viruses, and host. Evolution does not care who is steering.

In the exam room the same substance becomes detective work. He will ask a stranger who resembles his grandmother whether she is straining, what color it is, whether it floats, whether it is hard to flush. The doctor-patient relationship has no ordinary social barriers. You meet someone and immediately enter the most intimate details of their life. That is an art as much as a science: keep a human conversation going while talking about stool. Fridman hears the therapist in it. Reisman agrees that psychology is a huge part of the job, from psychiatric emergencies and intoxicants to the pediatric work of reassuring parents that a child does not need an intervention.

The ER, he says, is where you see humanity at its most raw. People come when they are suicidal, too high to walk, or when a child has been abused. It is the all-purpose waste bin for what people do to themselves and to others. The other truth is that the work can become ho-hum. Doctors get used to a heart attack, to a baby half out, and go home to dinner. Writing helps him keep the fascination. Medical problems are a great equalizer. Chekhov, who treated peasants and aristocrats, wrote that they all have the same ugly bodies. Under expensive clothes the failure modes are shared, and so is the worry that the poop turned green today. Reisman reads a short poem he wrote about faking it until the white-coat costume dissolves into a profession. The first time you ask a nice old lady about the color of her stool, it feels absurd. Then it becomes normal.

There is no sperm chapter in The Unseen Body, but there is a statistic Reisman has tweeted: an average man produces about 500 billion sperm, four to five times the number of people who have ever lived. Each is genetically unique, a possible Einstein, Feynman, or Hitler, and a possible child who would have died in childbirth. Sperm is also, he says, the only projectile bodily fluid that belongs to a healthy state. Vomit, cough, and sneeze expel something that should not be there. Sperm is packed with fructose for a journey of days in the female tract, then launched the way a touch-me-not flings seeds. The biological surprise is how many steps can fail. That it works as often as it does is, in his view, mostly a numbers game: people have a lot of sex. Fridman has read papers claiming the winner is not the fastest sperm but something closer to a randomized slaughter. Variety and redundancy, Reisman says, look like the point.

The liver is the gatekeeper for what we absorb. Blood from the gut, esophagus to rectum, does not go straight back to the heart. It goes to the liver to be examined, packaged, processed, detoxified. That is why alcohol and acetaminophen (Tylenol) injure it: both are metabolized there. The organ also packages cholesterol and fats, handles blood proteins and clotting factors, and processes bilirubin. It is the largest internal organ — skin is larger, but not internal — and when it fails, everything goes wrong. Reisman has posted that eating testicles will not raise libido, because ingested testosterone is metabolized in the liver before it reaches the blood. That is why testosterone comes as injection or foam, not a pill, while estrogen and progesterone can be taken orally.

Asked for a ranking of replaceable organs, he puts kidneys first. People have two, so a living donor can give one. The organ is small enough to stuff into the pelvis rather than sit in its original spot. Kidney transplants are also the most practiced. Liver is harder because of size, but it has a mythological talent that happens to be true: Prometheus's liver growing back each day is biologically in the right neighborhood. Remove or injure a piece and it regenerates. Hearts can be transplanted, and mechanical assists that help a failing pump are advancing fast; many did not exist when he left medical school and are now routine. The brain, as far as he knows, has not been successfully transplanted. Because the heart is a pump, it may eventually be the easiest organ to replace with a machine.

The craziest foods of Reisman's career come from the Far North. Traditionally, more than half the calories in an Inupiat diet came from blubber — marine mammal fat, fish fat, duck fat. He has eaten raw whale blubber, called muktuk: sliced thin, cold but not frozen, less chewy than people expect, with a smell of the sea. He has had beluga chowder and mikiyaq, whale meat fermented in whale blood. Arctic cooking used little fire because fuel was scarce. North-flowing rivers brought some driftwood from the Brooks Range, not enough for a heat-based cuisine. Seal and whale oil lamps were for light and a little warmth. Eating raw, two Inupiat hunters told him on the spring ice off Barrow, is the most essential cultural marker. One man who is half white bites the head off a raw bird to prove he belongs.

As a doctor he was used to knowing fat as the most maligned body part and the culprit in an obesity epidemic. In Arctic Alaska, fat has always meant health and survival. The whole story of human life there, he says, is basically a tale of fat. During spring whaling in Barrow, a captain raises a flag over his house and the town is welcome to come take a share. Reisman rounded a corner onto a lawn covered in blubber, the local equivalent of a plush suburban lawn, and found a bowhead whale heart the size of a yoga ball. The stump of aorta attached to it was as thick as his thigh. He spent about forty-five minutes looking.

The travel bug hit before medicine. Right after NYU, where he studied math and was not enjoying college, he interned for six months in Saint Petersburg, researching how Greenpeace, WWF, and the World Bank were trying to push Russia's timber industry toward sustainability after the Soviet collapse. He went back four more times, learned Russian, and twice reached Kamchatka. What stayed with him were older Russian women. He met few old men, which he takes as a comment on male life expectancy. A blind Koryak woman who looked like the most rural person imaginable would not stop talking about Dostoevsky and Tolstoy. Give people an excellent early education, he says, throw hardship at them, let them cook in it, and they come out fascinating. In remote northern villages he also saw the same family fights and bickering he knew from the New Jersey suburbs. Take modernity away and humans fill the space with their own complexity.

Fridman asks about the war in Ukraine. Reisman calls it tragic and seemingly pointless, then notes that destruction and a beaten-down populace are a long thread from the Mongol invasions through tsars, Soviets, and Putin. He is more at home on the biology of war. Someone, possibly with a nod to Walt Whitman nursing in the Civil War, has said war is the best medical school. Iraq and Afghanistan reworked civilian trauma care: tourniquets, whole-blood transfusion instead of separated components, battlefield pain control from ketamine injections to fentanyl lollipops. The Department of Defense and DARPA fund moonshot experiments most universities will not. The space program began military. His grandmother, from what is today Moldova, got typhus in World War II. Cholera and typhus advance in war along with trauma. Infection, not just blast injury, has always been the other teacher. Nothing, he says, reveals the honesty of human biology like war.

He once posted a photo of Shackleton's 1910s Antarctic medical kit: paregoric for pain, laxatives, only the essentials. Early-twentieth-century laxative use was a hangover from humoral theory — vomit, purge, bleed to balance the fluids — though a diet of seal and penguin is low in fiber, so the pills may have had a real job. Antibiotics did not exist. What he can put in a backpack today is many orders of magnitude more powerful. His own 2018 stint as a ship doctor in Antarctica was no Shackleton: a large cruise ship, 160 Japanese passengers with translators, several cabinets of injectables, pills, patches, and an EKG machine, plus free room and board. Every polar cruise needs an ER doctor. If someone gets a brain bleed at the end of the earth, the honest answer is they die. He likes that challenge. It hones the skills a fully staffed university hospital lets you outsource.

Mars, he says, takes the same problem to an extreme. Australia used to remove healthy gallbladders before Antarctic winter deployments so cholecystitis could not strand someone. People going to Mars might reasonably have appendix and gallbladder out in advance, and perhaps a cardiac catheterization to estimate heart-attack risk, even if caths do not fully predict events. He would love to go. He has a wife and two small children, so it is probably not in the cards. Space medicine looks to him like a wild extension of the high-altitude work he did in Nepal, where physiology already turns bizarre and is still poorly explained.

If this were his last day, Reisman would eat bone marrow, as much as he could get. On a birthday in 2002 he ate a kilogram and a half of king crab in Kamchatka, which was astonishing, but marrow still wins. Heat is all it needs. The fat for frying is already there, the bone is the vessel, and inside are the stem cells that spit out billions of white cells, red cells, and platelets every day. He prefers a larger animal only for volume; he will suck marrow from a chicken bone. He would eat it in Antarctica, which he had not realized was so mountainous. Ice and rock overwhelm the eye the way marrow overwhelms a plate. Icebergs come in unrepeatable geometries, often an unearthly blue. He mentions a U.S. Navy site that tracks the largest ones. The constant shedding of glaciers — snow inland, ice pushed to sea, bergs breaking loose — reminds him of the body, which is also always shedding, renewing, rebuilding.

College math at NYU stunned him because the digits disappeared. What remained were variables and concepts, a Platonic ideal that still explained the natural world. At the same time he was walking Central Park with Steve Brill, learning which wild plants were edible. Abstract algebra in one hand, a leaf you could put in your mouth in the other. The leap into the mush of biology felt large, but the connections are real: symmetry, fluid dynamics of blood and other liquids, bone to flesh to fluids of different consistencies. What he loves in bodies, and what software rarely has, is resilience. Half of a biological system can fail and the rest still runs.

Building a humanoid as hardy as a body is, he thinks, very hard and unfinished. People growing artificial organs have learned that celebrity stem cells are not the whole answer. The extracellular matrix — the foundation that holds cells in shape — does a lot of the signaling. Put the right stem cell on the right matrix and it becomes the cell you want. Neuralink-style brain interfaces he finds feasible, but we need to know more. The unsexy version already in clinics is deep brain stimulation for Parkinson's: as a student he watched a neurologist turn a dial and saw a tremor vanish. Similar stimulation is being studied for eating disorders and severe OCD. Biology will adapt to whatever you shove in, or reject it. Current AI systems, Fridman notes, are not adaptable in that wild way. The playground is messy because the lives are real.

Reisman has tweeted that if you look back from far enough in the future, every doctor today will look like a total quack. There is a saying that by the time you finish medical school, half of what you learned is wrong, and the half-life is getting shorter. Tests still sometimes want the old answer. History is worse: for most of it, he thinks, doctors did more harm than good. George Washington died of a peritonsillar abscess, quinsy, after being bled. Medical error remains a large cause of death. The humility this demands is not optional. A drug can make perfect mechanistic sense, help twenty patients in a row, and still fail or harm once you run the study. The stories doctors tell themselves about why treatments work are often wrong.

The experiments that humbled him most are sham surgeries. Arthroscopy to clean up a knee looked obviously useful until a trial put some patients to sleep, cut the skin, and did nothing inside; it was not clear the real operation helped. Stents for stable angina — chest pain on stairs that eases with rest — looked even more obvious. Increase the blood flow, how could it not work? Sham catheterization suggested it might not beat placebo. Fridman argues that future medicine will find today's practice 19th-century: a few minutes, a few complaints, almost no longitudinal data, then a guess. Reisman agrees it is humbling, and that medicine still runs on gestalt. In an ER you hear that a patient just does not look good, with no number to point at, sometimes just a change in skin color. Wearables already collect reams. The unused potential includes predicting who will have a dangerous drug reaction from their genome.

Paul Farmer is one of the people who most shaped him. Farmer pioneered global health, founded Partners in Health in Haiti, later Rwanda and elsewhere, and even as a medical student flew back and forth between exams. Tracy Kidder's Mountains Beyond Mountains is the book Reisman recommends. In Calcutta and Nepal he saw how unevenly modern medicine is spread. Children under five still die in large numbers from diarrhea that oral rehydration could treat, and from bacterial pneumonia that amoxicillin — pennies — could often stop. Families cannot always afford IVs and a hospital bed. Lex closes the episode with Farmer's line: the idea that some lives matter less is the root of all that is wrong with the world. Reisman's addendum is practical. Science should advance, and we should not forget that hundred-year-old treatments still save lives where they are simply not available.

Advice to young people comes down to one thing he can specify: become passionate about something and follow it wherever it takes you, without first calculating the career. After college he went to Russia with no idea what it would become. Twenty years later the fuel is still burning. In 2003 he spent four months in Kamchatka, two of them without speaking English, and remembers lying on a hard wooden floor in a hunter's cabin feeling only luck. You never replicate that first high. The plan can be as crude as go far away and see something different, then follow your nose. Medicine is the job that happened to pack his loves into one: detective work, work with the hands, and a gestalt you only get after hundreds and thousands of patients. Doctor originally means teacher, and teaching students is an underappreciated pleasure of the work.

His own dark places, he says, are milder than those of the people he treats. Two adult realizations still shock him: no one knows what they are doing, and suicide is incredibly common across societies. He has never seriously planned it; the thought has crossed during stress, and he thinks it crosses most minds. In the ER, many who come in after an attempt carry childhood trauma, a parent who died by suicide, abuse. Those events leave scars in the mind; later alcoholism and drugs are often an attempt to escape memory. Some people, he says carefully, seem ruined in a way that cannot be fully fixed. Hopelessness is the risk factor he asks about. Fridman tells anyone listening who is struggling that they are in it together. Keep up the good fight.

Ice climbing made him look down and think about dying. Children changed the equation: now he thinks about insurance, disability, what happens to the people who depend on him. Fridman suggests those practical worries are a way not to look at the harder fact that consciousness ends. Reisman, as a student, was morbidly fascinated by the last seconds — a head injury, aspiration, falling oxygen, arrest; a heroin overdose that stops breathing, then the same cascade. Then the family walked in, devastated, and ripped him out of the science. The person who died, if you ignore the pain beforehand, can seem to go to sleep and not wake up. The suffering is financial, psychological, and annual, in the people who loved them. Those problems he can work on: be a good father, buy the policies. He does not know what to do with the philosophical remainder: why it ends, why consciousness exists, why we can suffer.

Asked for the meaning of life, he suspects why is a trick of the human brain. Outside our thoughts, the universe may not contain a why. Asking why this plant grows here, why the same deer tracks appear under the same tree every three days, why this leaf makes you vomit, had survival value. We extrapolated the tool onto questions it cannot close, including why life exists. Fridman offers a kinder reading: maybe evolution wants a stack of unanswerable questions that never hits bottom, so the search keeps producing better ways to live, and perhaps lets the universe learn something about itself. Reisman does not pretend to finish that thought. He has spent the conversation putting the tube, the mucus, the blubber, the marrow, and the scars on the table. The design is full of holes. It is also what let a doctor sit down and talk, honestly, about why any of it is here.