Of all the wonders witnessed by Sir John Mandeville, a 14th-century English knight, none was more astonishing than the “wondirfulle” fruit of a tree he encountered on his travels in India. This fruit resembled a gourd, but cut it open and you would find tiny flesh-and-blood lambs. Another medieval traveller, the Italian Friar Odoric, had also journeyed widely through Asia and had learnt about the same fruits from “persons worthy of credit”.
Other accounts suggested that when the fruit ripened, the result was a full-fledged lamb, or something very like it, attached to the stem of the plant by an umbilical cord. The lamb would graze near its roots, but when all the grass within reach had been consumed, the Vegetable Lamb would die.
Readers with a solid grasp of botany may already be aware that there is no such thing as a Vegetable Lamb. Indeed, there was likely no such person as Sir John Mandeville — his celebrated travelogue was written by persons unknown, and based heavily on previous works, including that of Odoric.
Yet this did not stop stories about the Vegetable Lamb from circulating, and being believed, among the cognoscenti of Europe for centuries. Baron von Herberstein, an ambassador to Russia nearly two centuries after the Mandeville travelogue became popular, confessed to being sceptical before becoming a believer after many “people of credence” told him they’d seen and tasted the delicious plant-animal hybrid.
“It took nearly four centuries after Mandeville’s writings appeared for European botanists and biologists to recognise the Vegetable Lamb as a myth,” write Cailin O’Connor and James Owen Weatherall in The Misinformation Age (2019).
Does that sluggishness reflect the failure of a particularly medieval mindset, or does it have lessons to teach us today?
Consider some slightly more recent cases. James Lind, a Royal Navy surgeon, is celebrated today for discovering that citrus fruit cured scurvy, after running a primitive clinical trial in 1747. The only trouble is that he did no such thing.
Lind conducted a trial all right, but it made next to no difference to anyone’s perception of citrus fruits. Both before and after Lind’s trial, they were thought by some sailors to be helpful, but Lind’s work made little impression. His Treatise of the Scurvy (1753) is a mass of confusion, although the brief description of the trial nearly 200 pages in is clear enough. Lind ended up recommending a boiled citrus syrup, and this proposal was widely ignored — which is no great shame, since boiling lemon juice destroys vitamin C and thereby renders it useless as a cure for scurvy.
Citrus fruit was embraced by the Royal Navy half a century later, and not because of a clinical trial but because it was recommended by a high-status doctor, Sir Gilbert Blane. Still later, the “limeys” lost confidence in the cure. Stale, badly stored lime juice contains almost no vitamin C but, in the age of steam, ordinary sailors rarely got scurvy anyway because voyages were quick and regular refuelling stops were required. Polar expeditions were another matter, and in the late 1800s were frequently struck by scurvy despite the use of (stale) lime juice.
At the same time, germ theory was emerging and the idea that scurvy was something to do with citrus fruit began to seem quaint. As a result, Robert Falcon Scott was advised by medical experts that scurvy was caused by toxins called ptomaines, and his Antarctic expeditions were afflicted by scurvy more than 150 years after Lind’s “discovery”. Ptomaine poisoning is no more a real explanation for scurvy than the Vegetable Lamb is a real animal.
Ninety-nine years ago, the Korean newspaper Jungoe Ilbo published a story titled “Strange Harm from Electric Fans”, warning that having a fan running too close to you might cause death as you choked on your own carbon dioxide. (It won’t.) For decades, Korean newspapers continued to run articles about people dying in the presence of fans, whether or not there was any reason to believe the fan was to blame.
Why do we believe things that aren’t true? Two fashionable views are that we believe falsehoods because of political polarisation, or that we believe them because of emotional triggers such as fear, lust or greed. That explains why the political party faithful are willing to believe almost any smear about the hated enemy, while closing their eyes to wrongdoing on their own side — and why people will send money to strangers on the internet claiming to be Nigerian princes.
But neither tribalism nor greed explains the beliefs that your desk fan could kill you, that citrus fruit doesn’t prevent scurvy and that somewhere in Asia lambs grow on trees. Nor do they explain why these false beliefs persisted for so long.
For O’Connor and Weatherall, the point of the Vegetable Lamb story is that most of what we believe, we believe because everyone around us believes the same thing. From the belief that fresh vegetables are good for you to the idea that the Earth is basically spherical, our worldview reflects the worldview of the society in which we live.
The world can be a confusing place. Seeing white fluff bursting from cotton plants for the first time, it is not surprising that Europeans perceived a resemblance to lamb’s wool. Sailors on fast-moving steamships derived no antiscorbutic benefit from stale lime juice — and needed none.
When reality supplies us with signals that are mystifying (white fluff on a plant) or inconsistent (with or without lime juice, scurvy may or may not develop) or long-delayed (cigarettes dramatically raise your risk of lung cancer) it is hardly a surprise that we turn to each other for information.
Or we may turn to the experts, who will sometimes have a clearer view of what is going on. (Not always: Scott’s advisers were fretting about ptomaine poisoning.) Yet we still have to decide who we should regard as having relevant expertise. That might be a scientist, or a YouTube influencer, or Wikipedia, or the output of a large language model — but in any case we will take cues from others as to who counts as “persons worthy of credit” and who does not.
“Most of us get our false beliefs from the same places we get our true ones,” write O’Connor and Weatherall. It is a sobering thought.
I draw three lessons. First, if most of our beliefs are handed to us by the society in which we live, it is vital that our society itself values truth and truth-telling. Second, it is never a bad idea to stop and think for a moment about what other people tell you.
And third, contact with unfamiliar views is healthy. What eventually punctured the Vegetable Lamb myth was that every time Europeans journeyed to Asia in search of the creature, the locals found the whole business hilarious.
Written for and first published in the Financial Times on 19 Aug 2026.
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