pplpod

The human genome has roughly 20,000 to 25,000 genes, but the gut microbiome carries about 100 times more, making you genetically about 1 percent human. This episode tours the 10 to 100 trillion microbes inside you, which make up as much as 55 percent of the dry mass of stool. The stomach is nearly sterile acid, though Helicobacter pylori survives by wrapping itself in ammonia. The colon holds the...

Around 1800, French orphan Martin Fugate settled along Troublesome Creek near Hazard, Kentucky, and married Elizabeth Smith. Both unknowingly carried a rare recessive gene for methemoglobinemia, and four of their seven children were born with vivid blue skin. In a valley cut off from roads and railroads, descendants married into the local Combs, Ritchie and Smith families, and the trait resurfaced...

Chemist John Dalton believed blue fluid in his eyes filtered out red and green, and asked that his eyes be preserved after his death. In 1995, scientists analyzed DNA from the eye, kept since 1844, and found a genetic variation instead. This episode explains color vision deficiency, which affects about 8 percent of men and 0.5 percent of women with red-green types. True grayscale vision, monochrom...

In February 2015 Cecilia Bleasdale photographed a lace dress at the Cheshire Oaks Designer Outlet in England and sent it to her daughter Grace, who was getting married on the Scottish island of Colonsay. Grace saw white and gold. Cecilia, who had just seen the dress in person, saw blue and black, which it was. After the wedding, singer Caitlin McNeill posted the photo on Tumblr, a BuzzFeed poll to...

The room around you feels like raw reality, but this episode argues it is an edited, slightly delayed guess. Using illusions as a diagnostic tool, it follows Richard Gregory's three tiers. Physical illusions bend light before it reaches the eye, like the stick in water Ptolemy noted around 150 AD, or mountains that look close on a haze-free day. Physiological illusions come from tired hardware, li...

The average person spends about two hours a night dreaming, adding up to five or six years of life. This episode starts with the word itself: in Old English, dream meant noise, joy or music, and only took on its sleep meaning in the 13th century under Old Norse influence. In Bronze Age Mesopotamia, Egypt and Greece people did not have dreams, they saw them, as visits from gods or ancestors. Around...

Just as you drift off, your whole body jolts and you feel yourself fall. Sleep medicine calls this a hypnic jerk, or sleep start: a form of myoclonus, a brief involuntary muscle contraction that happens only at sleep onset as you cross into non-REM sleep. It can be a full body flex or a single kicking leg, often with a racing heart, quick breathing and sweat. Researcher Ian Oswald documented how t...

At the summit of Mount Everest, 29,032 feet up, the air holds the same 20.9 percent oxygen as at sea level, yet breathing it can kill. This episode explains the death zone, which begins at 8,000 meters, about 26,246 feet, and covers only 14 peaks in the Himalaya and Karakoram. Swiss doctor Edouard Wyss-Dunant first called it the lethal zone in 1953. The problem is pressure: it falls from about 1,0...

In May 2018 a one second audio clip divided the internet: in a Twitter poll of more than 500,000 people, 53 percent heard Laurel and 47 percent heard Yanny, and each side found the other impossible to understand. The recording began in 2007, when opera singer Jay Aubrey Jones recorded about 200,000 reference pronunciations for Vocabulary.com in a makeshift New York apartment studio. Eleven years l...

Bored office workers yawn, and so do paratroopers seconds before they jump. This episode explores chasmology, the study of yawning, starting with the reflex itself: a slow inhalation, a peak of involuntary muscle stretching called the acme, then a fast exhalation, a sequence seen in fetuses on 4D ultrasound at 30 weeks. The airway dilates to three or four times its size, and the rumble in your hea...

That maddening moment when a word you know refuses to come out has a clinical name, lethologica, and a long research history. William James described its mild anguish in his 1890 book The Principles of Psychology, and Sigmund Freud blamed repressed thoughts. The empirical breakthrough came in 1966, when Harvard researchers Roger Brown and David McNeill read people definitions of obscure words like...

The oldest known impacted wisdom tooth belongs to a Magdalenian woman who lived in Ice Age Europe between 13,000 and 11,000 BCE. Third molars were grinding tools for raw roots, nuts and uncooked meat, and the heavy chewing load stimulated osteoblasts to build longer, bigger jaws. Agriculture about 10,000 years ago, cooking and then the Industrial Revolution softened diets, jaws grew shorter and wi...

Tickling is two different things. In 1897 psychologists G. Stanley Hall and Arthur Allen separated knismesis, a light moving itch that annoys without laughter and is shared with animals like scratching dogs and twitching horses, from gargalesis, the harder pressure that brings helpless laughter and is found mostly in humans and other primates, though rats emit ultrasonic chirps when tickled. In 19...

In Catholic and Eastern Orthodox tradition, incorruptibility is the belief that divine intervention lets the bodies of some saints and beatified people avoid normal decay through autolysis and putrefaction. The Catholic Church verifies claims under canon law: bishop authorized inspections, sometimes a pontifical commission, a written medical report, and resealing with ribbons and wax. Witnesses of...

Most people see color through three cone types tuned to short, medium and long wavelengths, but the common ancestor of all vertebrates had four. During the nocturnal bottleneck, when early mammals hid from dinosaurs, rods mattered more than cones and mammals lost two cone types, and primates later re-evolved a third, mainly to spot ripe fruit. Birds kept the fourth cone and see into the 300 to 400...

Up to half of all people will wake at least once unable to move, with crushing pressure on the chest and a dark figure in the room. This episode explains sleep paralysis as an overlap of REM sleep and waking: serotonin, the wake signal, and acetylcholine, which drives REM, fire at the same time, so the mind is alert while REM atonia keeps the body locked. Dream activity bleeds into perception as s...

In 1953 Nathaniel Kleitman and Eugene Aserinsky noticed sleepers' eyes darting beneath closed lids and found that people woken in those windows reported vivid dreams. EEG later showed REM sleep looks like wakefulness: fast, desynchronized signals, theta rhythms in the hippocampus and gamma waves of 40 to 60 hertz. Acetylcholine floods the brain while histamine, serotonin and norepinephrine drop to...

Paris syndrome is a rare, acute form of culture shock documented mainly among Japanese visitors to the French capital. Its psychiatric symptoms include delusional states, depersonalization, derealization and a conviction of being persecuted by locals, and its physical ones include dizziness, sweating, vomiting and a racing heart. A 2004 paper by Viala and colleagues in the French journal Nervure n...

A cat whose left foreleg was amputated months earlier still tries to scoop litter with the missing paw, and between 50 and 80 percent of human amputees likewise feel a limb that is gone. This episode separates phantom limb syndrome, the often painless sense of presence, from phantom limb pain, and describes kinetic, kinesthetic and exteroceptive sensations, including phantom itches and telescoping...

The polygraph is a 2 billion dollar American industry running about 2.5 million tests a year, yet it detects no lie. Its rubber tubes, blood pressure cuff and finger plates record breathing, cardiovascular activity and skin conductance, the signs of fight or flight arousal. Examiners prime subjects with a rigged stim test card trick, then compare reactions to irrelevant, control and relevant quest...

Jerusalem syndrome is an umbrella term for religiously themed delusions and psychotic episodes triggered by a visit to the city, and it crosses Christian, Jewish and Muslim lines and sometimes affects secular visitors. The pattern long predates jet lag. The 15th century itinerary of Dominican monk Felix Fabri describes pilgrims wandering the hills reenacting biblical suffering, and English mystic...

In early 1936, an 86 year old Ivan Pavlov lay dying of double pneumonia and asked a student to sit by the bed and record his final physiological sensations. This episode traces how the eldest of 10 children of a village Russian Orthodox priest in Ryazan ended up there. A severe fall from a wall at age seven kept him out of school until 11, and he later left a theological seminary after reading Dmi...

Hiccups have a folk reputation as a sign that someone is talking about you, a belief found in Slavic, Turkish and Luo traditions, but the medical reality is mechanical. The reflex, called singultus from the Latin for a sob, is a two part event: a sudden involuntary spasm of the diaphragm pulls air in, and about 35 milliseconds later the glottis snaps shut, and that collision makes the hic sound. E...

Horripilation, the pilomotor reflex better known as goosebumps, begins when the sympathetic nervous system releases norepinephrine onto tiny erector pili muscles that anchor the skin's basement membrane to hair follicles. Recent anatomy shows one muscle often controls a cluster of follicles, and its contraction squeezes sebaceous glands to push oil to the surface. The follicle's deep bulb gives th...

A bone marrow transplant can change a patient's blood type, because the donor's stem cells take over red cell production. This episode explains why that is possible: a blood type is the set of antigens on red blood cells, policed by antibodies in the plasma, and the International Society of Blood Transfusion recognizes 49 blood group systems, including Kell, Duffy, Kidd, and Lewis. Many of those v...