Contrary to modern stereotypes, people living during the European Middle Ages (roughly 500 to 1500 AD) were not foolish; notably, virtually every educated medieval scholar knew perfectly well that the Earth was a round sphere rather than a flat disk. However, because medieval natural philosophers lacked microscopes, telescopes, and global exploration networks, they relied on a blend of ancient Roman encyclopedias like Pliny the Elder’s Natural History, Christian allegory, and travelers’ rumors to explain the mysteries of nature. The result was a fascinating medieval worldview populated by seven extraordinary beliefs that treated mythological marvels as everyday scientific facts.
- 1. Barnacle Geese Grow on Trees Instead of Hatching From Eggs
- 2. Animals Could Be Arrested, Hired Lawyers, and Stood Trial in Court
- 3. Beavers Bite Off Their Own Testicles to Escape Hunters
- 4. The Vegetable Lamb of Tartary: Sheep Growing on Plant Stalks
- 5. Bear Cubs Are Born as Featureless Lumps and Licked Into Shape
- 6. A Wandering Womb Crawls Around Inside the Female Body
- 7. Sperm Comes From the Brain and Right vs. Left Testicles Determine Sex
1. Barnacle Geese Grow on Trees Instead of Hatching From Eggs
Throughout the Middle Ages, nobody in Britain, France, or Ireland had ever seen a barnacle goose (Branta leucopsis) build a nest or lay an egg. The reason is simple: barnacle geese breed exclusively on remote Arctic cliffs in Greenland and Svalbard during the summer before flying south to winter along European coastlines. Because the concept of long-distance bird migration across oceans was poorly understood, medieval naturalists concluded that barnacle geese did not hatch from eggs at all.
Instead, observing clumps of stalked goose barnacles (crustaceans with feathery feeding tentacles inside white shells) clinging to rotting driftwood washed up on beaches, twelfth-century scholars like Gerald of Wales wrote in all seriousness that barnacle geese grew like fruit hanging by their beaks from coastal fir trees or rotting ship timbers, eventually ripening and dropping into the sea as fully feathered birds. This belief had a hilarious culinary benefit: because the geese grew from wood and water rather than mating in the flesh, medieval Catholic authorities classified barnacle geese as “fish” rather than “meat,” allowing hungry monks and nobles to eat roasted goose guilt-free during the forty fasting days of Lent—until Pope Innocent III finally banned the loophole in 1215.
2. Animals Could Be Arrested, Hired Lawyers, and Stood Trial in Court
In medieval legal philosophy, God’s moral and civil law applied not only to human beings, but to every living creature in creation. Consequently, between the thirteenth and seventeenth centuries across France, Switzerland, Germany, and Italy, domestic animals that committed violent crimes—most commonly free-roaming pigs that wandered into cottages and killed infants—were formally arrested by the town bailiff, locked inside the exact same stone jail cells as human prisoners at public expense, and brought before a secular judge for a full criminal trial.
In a famous 1386 case in Falaise, France, a sow accused of fatally mauling a child was assigned a defense lawyer, tried before witnesses, dressed in human clothes (a waistcoat, breeches, and gloves), and publicly hanged on the town gallows by the professional executioner. Meanwhile, if a plague of field mice, weevils, or locusts destroyed a village’s barley crop, the pests were tried in absentia before an ecclesiastical church court: a court-appointed defense attorney solemnly argued that the insects were merely obeying God’s command to “be fruitful and multiply” and could not appear in court because village cats were waiting to ambush them along the road, before the bishop issued a formal writ of excommunication ordering the beetles to vacate the parish within three days.
3. Beavers Bite Off Their Own Testicles to Escape Hunters
Medieval bestiaries—lavishly illustrated natural history books that used animal behavior to teach moral lessons—were obsessed with the Eurasian beaver. In the Middle Ages, a waxy orange secretion used by beavers to mark territory, called castoreum, was prized across Europe as an expensive painkiller, fever reducer, and perfume ingredient (and actually does contain salicylic acid derived from the willow bark beavers eat).
Medieval writers erroneously believed that castoreum was produced inside the beaver’s testicles rather than in internal scent sacs. According to every medieval bestiary, when a smart beaver realized it was being chased by a hunter and dogs, it knew exactly what the hunter wanted; so, to save its own life, the beaver would stop, bite off its own testicles with its sharp teeth, and throw them at the hunter’s feet. If a second hunter chased the same beaver later, the animal would simply stand up on its hind legs and lift its tail to show that its “treasure” was already gone, prompting the hunter to walk away—an allegory used by priests to teach Christians to cast away worldly sins and riches to escape the Devil.
4. The Vegetable Lamb of Tartary: Sheep Growing on Plant Stalks
Before cotton plantations were familiar to Northern Europeans, travelers returning from Central Asia and India reported seeing a miraculous plant bearing soft, white wool that grew directly out of pods on bushes rather than being sheared from the backs of sheep. Filtered through centuries of exaggerated storytelling—most famously in the fourteenth-century Travels of Sir John Mandeville—the ordinary cotton plant morphed into the Vegetable Lamb of Tartary, or the Borametz.
Medieval encyclopedias described and illustrated the Borametz as a literal, living flesh-and-blood lamb with hooves, ears, and fleece that grew attached at its belly button to a flexible green plant stem rooted in the soil. According to the belief, the plant-lamb bent its stalk downward to graze on all the grass growing in a circle around its base; once it ate the last blade of grass within reach of its stem tether, both the lamb and the plant withered and died, unless hungry wolves—the only carnivores that loved eating this plant—devoured it first.
5. Bear Cubs Are Born as Featureless Lumps and Licked Into Shape
When a female brown bear gives birth inside her dark winter den in January or February, newborn cubs are remarkably tiny and underdeveloped—weighing less than a pound, blind, hairless, and pink, allowing the hibernating mother to nurse them easily without exhausting her fat reserves. Because no medieval hunter dared crawl into an occupied bear cave in mid-winter with a torch to observe newborns closely, naturalists relied on an ancient claim passed down by Pliny the Elder and Isidore of Seville.
Medieval bestiaries stated as absolute biological fact that mother bears gave birth prematurely after thirty days to lifeless, eyeless, legless white blobs of raw flesh no bigger than a mouse. Upon giving birth to this formless lump, the mother bear spent days patiently sculpting the meat with her warm, rough tongue—literally licking out its legs, ears, eyes, and claws until it took the shape of a bear cub. This weird medieval belief is the direct origin of our modern English idiom of taking an unruly recruit or rough draft and “licking it into shape.”
6. A Wandering Womb Crawls Around Inside the Female Body
Inherited from ancient Greek physicians like Hippocrates and Aretaeus and adapted into medieval medical texts, doctors for centuries believed that the female uterus was not anchored firmly in place by ligaments inside the pelvis, but was instead an quasi-independent, mobile creature possessing a keen sense of smell that could wander freely up and down through a woman’s torso.
If a woman suffered from shortness of breath, fainting spells, loss of voice, or emotional distress—a condition labeled “hysteria,” from the Greek hystera meaning womb—medieval physicians diagnosed that her uterus had detached and crawled upward toward her liver, lungs, or throat, crowding her heart. Because doctors believed the womb loved sweet fragrances and hated foul odors, the standard medieval medical treatment to coax the wandering womb back down to its proper home was “fumigation”: holding foul-smelling substances like burned hair, sulfur, or rotting cabbage directly under the patient’s nose to drive the womb downward, while placing sweet-smelling rosewater, musk, and cinnamon herbs between her legs to lure it back into the pelvis.
7. Sperm Comes From the Brain and Right vs. Left Testicles Determine Sex
Without microscopes to observe human spermatozoa or female ova, medieval anatomy texts held deeply imaginative theories regarding human reproduction. Following ancient Hippocratic and Galenic traditions, many medieval scholars believed that human semen was originally distilled from cerebrospinal fluid inside the brain and traveled down through veins behind the ears and along the spinal cord—which led to the widespread belief that cutting the veins behind a man’s ears would render him permanently sterile.
Furthermore, because medieval medicine associated the right side of the body with heat, strength, and masculinity and the left side with coolness and femininity, encyclopedias taught that male babies were produced strictly by seed coming from the right testicle (or landing in the right side of the uterus), while female babies came exclusively from the left testicle. As a result, desperate medieval noblemen who wanted to guarantee the birth of a male heir were sometimes advised by physicians to tie a tight cord around their left testicle during intercourse—or in extreme rumored cases, have the left testicle surgically removed—so that only “male” seed could flow.
