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4 of History’s Strangest Scientific Theories

Near Space photography - 20km above ground
IM_photo/Shutterstock

Throughout the entirety of human history, we’ve strived continuously to understand the world—to come up with plausible explanations for natural phenomena that we may not fully grasp. Alas, as some of history’s strangest scientific theories demonstrate, we don’t always get it right. In fact, we’re frequently so wrong that many of these now-obsolete theories edge into outright absurdity.

To be fair, many of the theories we now know to have been incorrect could only correctly be assessed much later on. We’re always at the mercy of current advancements, both in thought and in technology; as we both gain better tools and develop deeper ways of thinking, we’re able to observe the world around us more accurately and get closer and closer to the truth of the matter.

That doesn’t stop our growing array of out-of-date theories from being laugh-out-loud funny, of course, but it’s worth remembering all the same.

These four theories may have fallen out of style long ago, but they’re still a testament to our thirst for knowledge—and the, er, creativity of our thinking.

Spontaneous Generation

Let’s start with the big picture: Where does life itself come from? For thousands of years, long before we knew anything about how reproduction actually worked, it was generally accepted that some forms of life just…came into being, spontaneously generating from non-living matter. How else could all those maggots have ended up in that hunk of rotting meat, we told ourselves? Or what about clams and oysters? They seemed simply to appear in the mud in or near bodies of water. How else could they have been made, if not from the mud itself? According to Aristotle, numerous living creatures—including an awful lot of insects—could spontaneously generate from a truly staggering array of materials that were expressly not alive, ranging from slime to dried sweat and from old wax to paper and books.

This line of thought can be found in the writings of numerous ancient civilizations, from the Babylonians to ancient Greece. What’s more, it persisted well into the Scientific Revolution. One seventeenth-century Dutch chemist and physician, Jan Baptiste van Helmont, even came up with several “recipes” geared towards generating particular creatures. Need some mice? Stick a sweaty shirt in a container with some wheat and wait 21 days. By the time the 21 days are up, said van Helmont, the wheat grains will have turned into mice. Scorpions more your speed? Carve a little pocket into a brick, fill it with basil, top it with another brick, and leave it in the Sun for a few days. The next time you check your little brick pocket, voila: You’ll find genuine, basil-grown scorpions waiting for you.

Italian biologist Francesco Redi was one of the first to challenge the idea of spontaneous generation. In 1668, he put chunks of meat into three separate jars—one left open, one covered with netting, and one completely sealed. Redi observed that, while maggots appeared on the meat of the open jar and the netting of the second jar, with flies laying eggs in both locations, the sealed jar remained maggot-free. As such, he determined, maggots did not generate spontaneously from meat, but rather that they—and all living things—originated from parents, the same way humans did.

Other scientists also conducted experiments challenging spontaneous generation over the next several centuries; however, it was Louis Pasteur, the creator of pasteurization, who finally settled the issue in 1859. Pasteur first boiled a meat broth in a flask with a curved neck to sterilize the broth, then let it sit for a while undisturbed. The flask’s unique neck, said Pasteur, would prevent any airborne microorganisms from making their way into the broth—so if spontaneous generation did, in fact, exist, then the broth should have no problem generating new life forms anyway. But as Pasteur predicted, the broth remained sterile—until the flasks were tipped such that the broth came in contact with the curved neck of the flask. At that point, it rapidly grew organisms, becoming cloudy and discolored, showing that life didn’t generate from the broth itself, but from already-existing organisms.

The Rain Follows the Plow

During the late nineteenth century, white colonists of European descent in the United States embraced the notion of westward expansion, fueled by factors such as the Louisiana Purchase, the Gold Rush, and the belief in so-called “manifest destiny.” As party after party traveled along the Oregon Trail, many observed that the Great Plains, hitherto known for its dry and arid climate, was suddenly bursting with green. This gave rise to the belief that farming and the cultivation of land, along with homesteading and settlement, had contributed to a permanent change in the area’s climate, making it much more humid and encouraging rainfall. Or, as naturalist Charles Dana Wilber put it in his 1881 book The Great Valleys and Prairies of Nebraska and the Northwest:

“Suppose now that a new army of frontier farmers—as many as could occupy 50 miles, in width, from Manitoba to Texas, could, acting in concert, turn over the prairie sod, and after deep plowing and receiving the rain and moisture, present a new surface of green growing crops instead of dry, hard baked earth covered with sparse buffalo grass. No one can question or doubt the inevitable effect of this cooling condensing surface upon the moisture in the atmosphere as it moves over by the Western winds. A reduction of temperature must at once occur, accompanied by the usual phenomena of showers. The chief agency in this transformation is agriculture. To be more concise. Rain follows the plow.” 

For a time, the belief seemed accurate; indeed, it was even endorsed by prominent climatologist Cyrus Thomas. “Seemed” is the operative word here, though. The land eventually dried out again, returning to its natural state and leaving homesteaders literally high and dry.

Today, we know that the wetness, which made for good farming at the time, was simply due to some unusual weather. The phrase “the rain follows the plow,” meanwhile, is looked upon solely as a prime example of the logical fallacy of correlation being assumed to mean causation.

The Four Humors

Charles Le Brun-Grande Commande-Les Quatre parties du jour
Preparatory drawing for the sculptors of the Grande Commande. Charles Le Brun / Public domain

Although evidence that suggests the concept of the humors dates back to ancient Egypt, Mesopotamia, and Indian Ayurvedic medicine, the theory as we know it crystallized in ancient Greece and Rome. Hippocrates is usually credited with developing the idea of the humors into a full medical theory. However, the Roman physician Galen both added to it and contributed to its continued use for centuries to come.

The theory of humorism posited that human health, both mental and physical, depended on the balance of four fluids, or humors, produced by the body: Black bile, yellow bile, phlegm, and blood. These fluids also corresponded to both the four elements and the four seasons—black bile was associated with Earth and autumn; yellow bile with fire and summer; phlegm with water and winter; and blood with air and spring—and, crucially, with certain temperaments, as well.

When you weren’t at your best, it was believed to be due to an imbalance in your humors. Feeling sad or depressed? You had too much black bile in your system and were, therefore, deemed “melancholic.” Angry or impulsive? You had too much yellow bile, making you “choleric.” Sluggish and unemotional? You had an excess of phlegm and were, therefore, “phlegmatic.” Excitable and overly enthusiastic? You had too much blood, making you “sanguine.” Physical illness also depended on your humors—and no matter what was ailing you, it was believed that balancing them all out would solve the problem.

Treatments aimed at balancing the humors ranged from personal hygiene to adjustments in diet and exercise—and, yes, actually draining the excess humors from your body. If you were too sanguine, for example, you might be bled, either with a good old-fashioned blade or with leeches. (Bleeding was a particularly prevalent practice during the Victorian era.) Myriad ways existed to induce perspiration, urination, defecation, and other bodily fluids and material, all of which were believed to help your humors reach the desired equilibrium.

Humorism has obviously fallen out of favor as a medical practice because it’s not at all accurate; as a metaphor, however, it thrives, both in literature and in some branches of psychology.

The Planet Vulcan

Astronomers have known about the planet Mercury since antiquity, but it was only in the seventeenth century that telescopic observation of the planet became possible (thanks, Galileo). However, just because it could be observed didn’t mean it was easy to observe; indeed, its proximity to the Sun made it quite challenging to keep an eye on. As a result, much remained unknown about Mercury for several more centuries—including a plausible explanation for something odd about its orbit: It wobbled. Specifically, the point at which Mercury passed closest to the Sun —its perihelion—advanced each orbit in ways that astronomers couldn’t predict.

French mathematician and astronomer Urbain Jean Joseph Le Verrier knew this and began working on the problem in the mid-nineteenth century. Per the prevailing belief of how gravity worked at the time, Sir Isaac Newton’s law of gravitation, this wobble should, in theory, have been caused by the gravitational influence of other celestial bodies nearby—namely Venus, Earth, Mars, and Jupiter. However, Le Verrier found that this wasn’t the case; no matter how he worked the equations, Mercury’s orbit continued to escape its predicted route.

So, he formulated the only logical hypothesis he could think of: The wobble was caused by the gravitational influence of some other nearby celestial body—one no one knew about yet.

It made sense then; after all, Le Verrier had previously identified Neptune by the same method (Uranus’ orbit wobbled, too). It seemed to make even more sense when physician and amateur stargazer Edmond Modeste Lescarbault reached out to Le Verrier about a strange shadow he had seen cross the Sun through his telescope in March of 1859. In 1860, Le Verrier announced the discovery of a previously unknown planet he believed explained Mercury’s strange orbital patterns: The planet Vulcan, so named for its closeness to the Sun.

The trouble was, no such planet existed. Alleged sightings remained elusive, and Le Verrier died in 1877 without having conclusively proven that Vulcan was, indeed, real. The final nail in Vulcan’s proverbial coffin came in 1915 when Albert Einstein published his theory of general relativity—the theory that would supersede Newton’s law of gravitation. Per Einstein’s theory, Mercury didn’t wobble in orbit due to the presence of a nearby planet; instead, the curvature of spacetime around the Sun resulted in Mercury’s perihelion advancing differently than it would in Newton’s gravitational system.

Although we now know there’s no such planet as Vulcan, theories about other hypothetical planets still pop up from time to time today. Some of them are more realistic than others; for example, Planet Nine may actually exist, whereas Nibiru—the massive object some believe will crash into the Earth at some point–probably doesn’t. Space really is the gift that keeps on giving.

Lucia Peters Lucia Peters
Lucia Peters is a writer and editor based in Washington, D.C. Her work has appeared at Bustle, The Toast, Crushable, The Gloss, and others. She also writes and manages The Ghost In My Machine, where she haunts readers several times weekly with spooky stories of the strange and unusual. Her first book, Dangerous Games To Play In The Dark, was published by Chronicle Books in September of 2019. Read Full Bio »