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We’ve all heard this saying, from our parents, friends, or from doctors themselves. “An apple a day” is an easy way to eat healthfully, and the phrase has a satisfying ring to it. However, the fruit doesn’t actually do anything to keep people out of the doctor’s office.

A 2015 peer-reviewed study that collected nutrition data from failed to find evidence of a link between apples and reduced doctor’s visits. Apples are still healthy, though; they contain a high amount of water, pair well with other healthy foods, and are high in potassium and fiber.

Goldfish are commonly assumed to be only capable of remembering their last trip around the bowl. Researchers at the Israeli Technion Institute of Technology put this to the test in 2009, when they demonstrated that the fish can actually .

They taught a group of young fish to come to eat when a certain sound was played, then released the fish into the wild; five months later, when the scientists played that same sound, the fish returned.

The Great Wall of China, one of the great wonders of the world, has been called the only man-made object to be visible from space. But in fact, the wall is mostly the same color and texture as the land around it, so it blends into its surroundings.

Even a Chinese astronaut, Yang Liwei, claimed he could not clearly see the wall from space in 2003. Look at these , and see if you can spot it yourself.

“Wait half an hour after lunch before you go back into the water,” parents tell their kids at the pool. This suggestion relies on the belief that all your blood will go to your digestive tract and will thus be unavailable to help keep your arm and leg muscles pumping as you swim.

In an article from Duke Health, that while the body does produce extra blood to help with digestion, it’s not enough to prevent your muscles from functioning normally.

Many high school chemistry teachers will use water as an example of a good conductor and warn you against leaving a hair dryer near the sink.  While this is true, it's a bit misleading: pure, distilled water without any impurities is actually a —it doesn't let electricity flow through.

The electrical charge goes through the salt, calcium, magnesium, and other minerals found in plain water, the scientific term for rainwater, tap water, and other water that hasn't been purified.

The Sahara, a massive, arid landscape that stretches across northern Africa, has often been dubbed the largest hot desert on the planet. However, the actual definition of a desert depends

Thus, as an area of 5.5 million square miles receiving under 200 millimeters of rain each year, the Antarctic Desert is actually the biggest desert on Earth.

The “five-second rule” is a familiar playground staple: It’s okay if your food falls on the ground, as long as you pick it up within five seconds. Unfortunately this rule does not have any actual basis in science. Five seconds is still plenty of time for  from the ground.

Alexander Graham Bell is a familiar figure on the roster of great inventors; you might remember his purple title card on the famous . But the actual origin of the telephone was a  than just Bell.

Charles Bourseul developed the idea for a communication device based on vibration between two diaphragms in France in 1854; Italian immigrant  developed a telephone in 1856 to communicate with his wife while he was sick in bed; and German Johann Philipp Reis tried to patent a similar device in 1861. All of these inventors led to Alexander Graham Bell's famous device being patented in 1876.

Bees, as people are told, are the most melodramatic of animals: If one stings you, it loses its life in the process. This myth is in fact only true for honeybees. A honeybee has on the back of its stinger, connecting the stinger to the insect’s abdomen; when the bee pulls away after burying its stinger in your arm, its whole body is ripped apart.

Most species, including bumblebees and the closely related hornets and wasps, do not have such violent anatomy and will live to sting again.

Mars is the "red planet," which is why it was named for the Roman god of war, right? Nope. This celestial body because the iron oxide, or rust, in the planet's soil floats up into its atmosphere.

In other words, from the perspective of the Curiosity Rover, Mars' sky is red, but the planet's surface itself includes brown, black, yellow, and green. Many show it as a tan or butterscotch color.

Organic farming methods are incredibly popular, as shoppers support food that is produced with . Scientists have attempted to demonstrate various nutritional benefits that would help justify organic food’s higher price tag, but conclusive evidence is few and far between.

A  in 2010 found no evidence linking positive health benefits to organic food, while a group of European scientists  in 2014.  The jury might be out on this question for a while longer, but regardless, organic farming is worth supporting because of its  and biodiversity.

People learn in elementary school that the right side of the brain is associated with intuition and creativity while the left side is associated with logic and analytical thinking. As a result, people are generally classified as either “right-brained” (more creative) or “left-brained” (more logical).

This concept is reductive compared to the brain’s actual functions, as different sections of the brain on both sides are . Studies utilizing CT and MRI scans have demonstrated that brain activity is similar when people perform similar tasks, regardless of their personalities.

In 1937, canine expert Will Judy wrote that dogs have poor vision and see the world in shades of gray. This belief has been widely accepted for decades, yet recent scientists have debunked it with close examination of canine eye structure.

Dogs’ eyes developed to help them hunt in the dark. They have a , and essentially see the world similarly to a person with red-green colorblindness. If you want to know what your dog is seeing, .

A common holiday myth warns us to steer clear of poinsettias because they’re toxic to humans. This myth dates back to 1919, when a child’s death was mistakenly attributed to the flowers.

Although the plants’ leaves do include chemicals that should not be ingested by humans—including milky saps and compounds used in photosynthesis—a 50-pound child would need to eat at least 500 to experience any ill health. 

This adage is more useful as a metaphor for probability. With an in the United States every year, not only can lightning strike in the same place twice, it likely will. The that "if there is a significant attraction between the bolt and the place it previously hit, it's more likely that the same place would be struck again."

Tall skyscrapers like the Empire State Building and the Willis Tower sport lightning rods to prevent electrical damage from reaching the main parts of the buildings.

In the past few decades, cancer screening methods have been developed to quickly detect many common forms of cancer. Some of these practices, like mammograms and ultrasound screenings for thyroid cancer, have become so ubiquitous that people assume early detection will lead to early recovery.

However, such assumptions can be dangerous when broadly associated with all types of cancer.  Each case is different, and while frequent screening is often useful (and beneficial for people with high risk factors), recent large studies have found that the survival of cancer patients  than it does on early detection.

Ostriches are often characterized as cowards, hiding from danger by sticking their heads in the ground. In fact, ostriches in danger use a : They flop down to the ground and lie still so that their heads and necks blend in with the soil. A nearby predator will, hopefully, believe the bird is already done for and move on.

If an adult ostrich is threatened and ready to fight, however, it can attack with its clawed feet. In fact, an is powerful enough to kill a lion.

In 1798, English cleric and scholar that the human race is growing at an exponential rate. This will eventually overburden the planet, leading to intense competition for resources. The population’s growth rate has, in fact, always been steady, and is currently in decline.

A pinpointed the rate at that time as about half of what it was before 1965. Widespread famine across the world is due much more to wealth inequality than it is to overpopulation.

One means of explaining addiction is tying it to genetic factors: The children of an alcoholic parent or parents are more likely to become alcoholics themselves. Genetic researchers have indeed , but there is not one single genetic factor that leads to the condition.

In addition, alcoholism is connected to societal and cultural factors. As neuroscientist David Haggerty writes in a : acknowledgment of these connections is necessary to develop effective support programs.

Many teenagers wish for the life of a sloth: These animals sleep all day and, when they do get up, they're so lazy, they barely move. That's the dream, right? Not quite. Sloths actually only sleep about eight to 10 hours a day in the wild, not so different from many humans.

While they are the slowest-moving mammals on the planet, their : Sloths maintain an even pace in order to operate at a lower body temperature than most mammals, thus allowing them to eat very little and spend less time looking for food. In fact, the most dangerous part of a sloth's life is its .

Conventional wisdom suggests that if your region is going to be hit by a hurricane, it’s best to close the windows and doors on the storm side of your house, but leave open the windows and doors on the other side. This supposedly avoids the build-up of pressure (and resulting explosion) inside the house.

The National Oceanic and Atmospheric Administration's  debunked this myth, attesting that since no house is actually airtight, there wouldn’t be enough of a pressure difference inside and outside to cause an explosion. They recommend closing all windows and doors to protect against flying debris.

“Wear a hat!” your mother told you as you left for school in the winter. The U.S. Army Field Manual used to state that leading to parents everywhere insisting upon hats as protection in the colder months.

But scientists have reevaluated this claim in recent years, finding that only 7 to 10% of heat is lost from your head. Wearing a hat is still a good idea, especially if your hair is wet, but it’s not as crucial as most people think.

This myth has been debunked countless times, yet still rears its head every Shark Week. Yes, sharks have a remarkable sense of smell, and yes, menstrual cycles do involve blood.

As was explained in a Popular Science article, “...if you suddenly got a super-heavy period and just expelled all of that blood in one go—which, to be clear, is not how periods work—you'd be dumping about 6 tablespoons of blood into the ocean.” And even if the sharks could detect that blood, they aren’t particularly interested in it.

People are taught they have five senses: sight, sound, smell, taste, and touch. In fact, humans have either many more or a few fewer, depending on how the term is defined. If a “sense” is a about the world and the body,” human senses also include proprioception (awareness of where our body is in space), balance, hunger and thirst, and the urge to expel waste.

On the other hand, if a “sense” is “a physical category of incoming information,” then there only three: mechanical information (touch, hearing, proprioception), chemical information (taste, smell, internal senses), and light information.

This phrase is common in milk advertisements and school cafeterias, but it may not have a basis in reality. Scientists are still investigating the best sources for the human body to get calcium, which is required for building healthy bones and teeth, along with other structural functions.

Findings so far show that there is (or otherwise a higher calcium intake) and protection against fractures.

Trees are the largest plants, filling forests and reaching up into the skies. So one would assume that trees are also the largest contributors to the planet’s supply of oxygen, using the process of photosynthesis to convert carbon dioxide and water from the atmosphere into oxygen and stored sugar.

In fact, the biggest contributor of this life-giving gas is marine algae. These tiny ocean plants live in massive colonies, where they’ve been photosynthesizing for millennia. Scientists have estimated that between 70 and 80% of the oxygen in the atmosphere is generated by these algae.

Sure, the sun looks yellow in the artwork of every kindergartener asked to draw one, but colors are less clear-cut once we move outside Earth’s atmosphere.

The sun’s light is actually an , which appears to the human eye as white. This light can also become scattered out into oranges, reds, and violets at sunrise and sunset, and can be separated into all colors individually in rainbows.

Mount Everest has claimed the lives of many a plucky climber hoping to scale its icy peak after succeeded in 1953. If you only count the height above sea level, this mountain is the world’s tallest.

But dive beneath sea level, and the crown goes instead to Mauna Kea, a mountain on the island of Hawaii. While Everest stands at 29,035 feet, Mauna Kea stands at about 33,500 feet: 13,796 feet above sea level, and 19,700 feet submerged.

Psychologists in the past have suggested that people only use a small fraction of their brains, leaving massive potential untapped. The myth has been linked to American psychologist William James, as well as to Albert Einstein.

This statement is though, according to neurologist Barry Gordon of Johns Hopkins: "It turns out though, that we use virtually every part of the brain, and that [most of] the brain is active almost all the time.”

It's hard to kill a cockroach. You can squash it, push it into another room, and bar the door, only to have it scoot under a crack barely perceptible to the human eye. This insect is 300 million years old; cockroaches lived that killed the dinosaurs and resist human attempts at extermination.

Scientists assumed that this would translate to the future, too—what's nuclear war to an insect that's already survived everything else? But might just outdo this tenacious bug: Studies in recent years have found that while cockroaches are less-susceptible to radiation than humans, the winner of the nuclear fallout survival contest may actually be the tiny flour beetle.