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Why Marco Polo Thought He Saw a Unicorn

The psychological explanations behind some explorers' fantastical tales.

Key points

  • Great explorers are credible witnesses to the unknown; but under stress, psychology, as well as physical reality, may influence their accounts.
  • Here we see the influence of prior frameworks for understanding, and of language, on explorer accounts of the bizarre.
  • The eyewitness accounts of explorers may bear directly on our understanding of eyewitness processes in the criminal justice system.
Matthew J. Sharps
Source: Matthew J. Sharps

Many great explorers have given their civilizations accurate pictures of the amazing complexities of other lands.

Then they've blown their reputations with completely ridiculous stories.

Take Marco Polo, whose explorations resulted in many accurate details of the Mongol realm of his time—and then, he claimed to have seen unicorns (Polo, 1948 ed.).

Practically nobody at the time believed anything Marco said—they called him "Il Milione," essentially Marco of a million lies; and the unicorn story couldn't have helped.

The problem is, he may in fact have seen one. Possibly even more than one.

Marco's "unicorn" description is of very large, ugly specimens. They did have one horn apiece, all right, but nothing else about them was particularly unicorn-ish.

It's highly possible that Marco Polo was looking at Indian rhinoceros, which actually are, in a sense, "unicorns"; they have one horn. Various antelope, in profile, can also look like they have one horn; between the antelope and the Indian rhinoceros, the idea of an animal "at least as big a horse, with a single horn," took root.

The language was wrong; once you hear the word "unicorn," you're picturing a horned horse, not a rhino or a sable antelope. The broad, inaccurate language contributes to an inaccurate prior framework for your understanding of what you see.

Big animal with a single horn. Check. Marco Polo had a prior cognitive framework for his understanding of the unknown, based on inaccurate, overly-broad language. Apparently, the rhino was the unicorn, for Marco.

How you get from the Indian rhinoceros and the sable antelope to the myth of a horny horse laying its head in the lap of a virgin, while angry villagers race up and beat it to death in a manner reminiscent of a chimpanzee troop enthusiastically murdering My Little Pony, I don't know. I suspect this myth tells us more about the psychology of the storytellers than it does about the rhinoceros or the antelope.

Marco Polo was a medieval explorer, and we often shrug off medieval reports on the basis of remote antiquity; yet in more recent times, similar eyewitness misinterpretations have occurred. Take Captain Meriwether Lewis of the Lewis and Clark expedition, explorer and secretary to Thomas Jefferson.

Under stress, human observational and interpretive powers become even worse than usual (see Sharps, 2022); and Lewis, near what is now Great Falls, Montana, was under stress. He and his Corps of Discovery were generally hungry, frequently lost, and well behind schedule. Lewis was desperately seeking, somehow, to get the hell out of Montana and find the Pacific Ocean.

Then he ran into the tiger.

There it was, briefly seen but apparently as tigerish as could be. Captain Lewis had discovered the American "Tiger-Cat" (Lewis, 1805). Many scholars think it was probably a wolverine, but Lewis was fairly insistent on a brownish-yellow animal "of the tiger kind."

There are no non-captive tigers in America. So what did Lewis actually see?

One reasonable North American possibility is a mountain lion, a puma, possibly including details from other observations of lynx or bobcats; but this suggestion is usually dismissed. Lewis certainly knew about pumas.

Yet pumas are amazingly elusive animals. Personally, living in an area frequented by mountain lions, I've seen their tracks twice in over thirty years, and an actual animal only once. I'm familiar with the concept of pumas, but I can't say that I know any of them personally.

What conceptsbased, perhaps, on overly broad language and prior frameworks for expectation—might Captain Lewis have had? As secretary to Thomas Jefferson, he would most likely have been aware of the President's passion for paleontology, and of the Presidential belief that the American West might contain living megafauna—ground sloths, or perhaps even Mastodons. Lewis would also have been aware of Jefferson's towering intellect.

This might have resulted in the prior framework like the following: "I can expect all kinds of weird animals out here, according to the smartest guy I ever met. And in the absence of zoos and Animal Planet, I've had very little practice observing pumas under different visual conditions anyway." Powerful but problematic concepts for dealing with a new world.

But could anyone mistake the smooth golden fur of a puma for that of a tiger? The only mountain lion I've seen in over thirty years out here was very, very old. His fur had deteriorated to a weird blend of greys and browns. He may have been disoriented; he was sauntering, in broad daylight, through a populated area.

You occasionally hear of a North American cryptid, a creature on par with Bigfoot, that resembles a black panther. Outside captivity, there are no black panthers in the U.S.; so, this creature is the subject of much speculation, especially on basic cable. He may be an errant jaguar, or a Space Panther foisted on us by Ancient Aliens, but he shouldn't be here.

But, briefly, he turned up in my yard—a senescent mountain lion. He apparently got tired; he lay down in the shade beneath a tree.

In the blazing midday sunshine, my eyes were not dark-adapted to the shade underneath the tree. So, to my eyes at that time, his ancient grey/brown fur, in the deep shadows, appeared black. And if only I'd had the right prior cognitive framework for this perception, I might have seen the Elusive American Black Panther.

Unfortunately, the Panther got up shortly and moved back into the sunshine, metamorphosing back into a very old mountain lion with serious fur problems and a skin condition. He wandered off and disappeared into the woods, where I suspect he took a nap.

Was Lewis' Tiger a puma, very briefly seen beneath the shading, mottling effects of foliage? If so, and with the right Jeffersonian prior framework, Lewis had his "Tiger-Cat."

Even great explorers have human nervous systems, and those systems can be deceived by prior frameworks for expectation, and by inaccurate, overinclusive language. Such influences, outside the forensic box, may have profound implications for the criminal justice system as well.


Lewis, M. (1805). Journal entry June 13-July 2. In Brandt, A. (Ed., 2002). The Journals of Lewis and Clark (Abridged). Washington, DC: National Geographic. (This is perhaps the most accessible reference available to the general reader. Many additional details, including more on the infamous Tiger-Cat, are given in the full edition of the Journals.)

Polo, M. The Travels of Marco Polo the Venetian. (William Marsden, Tr. & Ed., 1948), New York: Doubleday.

Sharps, M.J. (2022). Processing Under Pressure: Stress, Memory, and Decision-Making in Law Enforcement (3rd ed). Park City, Utah: Blue 360 Media.

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