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6 Common Myths About Sharks, Debunked

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Sharks are mysterious creatures. Even the origins of the word "shark" are unknown (though it might come from the Mayan word xok). Maybe that's what makes these 400 million year old denizens of the deep so captivating—and why they sometimes fill us with dread. Thanks to that general air of mystery, many myths and untruths about sharks have spread. Here are six for you to sink your jaws into. 

1. Sharks eat humans.

Negative public perception of sharks has proliferated their image as man-eaters since before Steven Spielberg’s summer blockbuster classic Jaws made you afraid to go into the water. But technically speaking, sharks don't seek out humans for food. When an attack does occur, it's most likely that the territorially-minded shark has mistaken the human for its actual prey (a seal, for example). In fact, most of the time, shark bites are actually “exploratory bites” in which a curious shark tries to determine if what it's biting is food. But despite the relatively slim chance of being attacked by a shark, there are some exceptions.

Of the hundreds of known species of sharks, only about a dozen are considered dangerous—including the great white, tiger shark, and bull shark—and are responsible for the most human attacks. The United States has the most recorded attacks, according to the International Shark Attack File; 1,022 total have been recorded between 1670 and 2012. Though Australia is second in total attacks, it has the most reported fatalities (144 as of 2012).

According to the Global Shark Attack File (GSAF), a similarly-named resource that seeks to “provide current and historical data on shark/human interactions” to the public, shark attack indices are divided into five separate categories. The most common categories are “Provoked”—in which “the shark was speared, hooked, captured or in which a human drew ‘first blood’”—and “Unprovoked,” which results when “a shark perceives a human as a threat or competitor for a food source.”

2. Sharks may not hunt and eat humans, but they're all vicious predators.

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There are over 400 different species, so there's no such thing as a typical shark. Yet popular opinion tends to veer towards the great white or the hammerhead out of sheer fascination and fear, thus propagating the myth that all sharks are dangerous and bloodthirsty hunters. While those species—and others such as the blue shark or the mako shark—are apex predators that reside on the top of the food chain, there are plenty of other species of sharks that go against the misconception that all sharks are predatory.

Take the dwarf lanternshark, for instance. This little guy, found off the coast of Venezuela and Columbia, is possibly the smallest shark in the world and can fit in the palm of your hand, reaching a maximum length of 21 centimeters. It’s so little of a threat, in fact, that even fishermen discard them if caught because they’re too small. On the opposite end of the spectrum, the whale shark (above)—the largest fish and shark of them all—reaches lengths up to 40 feet or more, and is a migratory filter feeder whose diet consists of mostly plankton. Though they are still carnivores, these swimming school bus-sized behemoths are so low key that they sometimes allow swimmers to hitch a ride on their dorsal fins.

3. If a shark stops moving, it will die.

Most sharks don't have to constantly swim to breathe or to stay alive. The majority of species use a process called “buccal pumping,” named after the cheek muscles they use to physically filter water into their mouths and over their gills, and can alternate periods of activity and rest.

But about two dozen species—including the great white, the whale shark, and the mako shark—are known as “obligate ram ventilators,” meaning it is mostly essential for them to keep moving to stay alive. Instead of breathing via buccal pumping, obligate ram ventilators pass water through their opened mouths and over the gills while in constant swimming motion so as not to asphyxiate. It's actually easier for these particular species of sharks to keep moving than to stay still, but it is possible for them to catch a break every once in awhile to rest up for a moment before swimming off again.

4. Sharks have endless rows of teeth.

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Sharks don't come out of the womb outfitted with endless rows of teeth. Technically, the serrated and pointy pearly whites just regenerate as needed.

A human tooth rests in a socket and falls out once during adolescence. But a shark’s teeth are attached by soft tissue to the skin covering the jaw, and easily fall out if they wear out or break. The teeth in a shark’s mouth are arranged in progressive rows, and should a tooth fall out, the next one behind it moves up to take its spot, like a rotating dental Rolodex. Some sharks can produce up to eight rows of teeth at once, and it takes a shark as little as 24 hours to produce a replacement tooth. With an average lifespan of 20 to 30 years, a shark can use thousands of teeth over its lifetime. Take the spiny dogfish shark, which holds the record for the longest lifespan at 100 years, and we’re looking at quite a lot of teeth!

5. A shark is just a dumb animal with a brain the size of a walnut.

Maybe it’s because of species like the tiger shark—which might seem dumb because they’re like swimming vacuums, eating almost anything in their paths—that this myth has spread far and wide. But the truth is, a shark’s brain is a complex organ belonging to a large and sophisticated animal.

A full-grown great white shark brain measures about 2 feet long and is a linear Y-shaped string of millions of neurons that arranges its functions into hind-, mid-, and fore-brain groups (as opposed to a human brain, which is folded into a compact, circular cluster). Almost two-thirds of the shark’s brain is devoted to its olfactory organs, highlighting how important it is for a shark to have an acute sense of smell. It’s so huge because certain olfactory stimuli—such as being able to identify prey, recognize aquatic territorial markers, or to find potential mates—are of the utmost importance for the shark’s essential wellbeing.

Any way you look at it, sharks are intelligent creatures that are astutely aware of their environment—so intelligent, in fact, they can even be trained!

6. Sharks don't get cancer.

You’ve heard of disingenuous snake-oil salesman, right? Well how about the shark cartilage salesman? Certain alternative health and nutrition stores sell shark cartilage as a means to ward off cancerous diseases based on the anecdotal evidence that sharks don’t get cancer. There are even books that promise a cure.

But it's a myth—you can read a little about how it got started here. The truth is that there are hundreds of cases of benign and cancerous tumors in sharks that have been reported in science and medical journals. Researchers, including John C. Harshbarger and Gary Ostrander, also proved the myth false by providing evidence of a shark’s ability to get cancer in a presentation of 40 separate cases of cancerous tumors in sharks at the American Association of Cancer Research in June 2000.

This myth isn't just dangerous to people suffering from cancer—because guess what? Shark cartilage doesn't cure cancer—but to sharks, too: It's led to a multi-million dollar industry and decimated shark populations. "North American populations of sharks have  decreased by up to 80 percent in the past decade, as cartilage companies harvest up to 200,000 sharks every month in US waters to create their products," writes Christie Wilcox in a 2011 Scientific American post.

The bottom line? Sharks do get cancer. Anyone who says otherwise is uninformed—or selling something.

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Big Questions
Why Do Dogs Howl at Sirens?
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A dog's behavior can often prove confusing to their human colleagues. We know they like to eat their own poop, but puzzle at their motivations. We're surprised when dogs give a ladybug the same greeting as a home intruder.

Topping the list of eccentric canine behavior: Why do dogs howl at sirens? Is there some genetic predisposition to responding to a high-pitched alarm from passing ambulances or police vehicles?

As it turns out, the reason dogs howl at sirens is because of their ancestry—namely, the wolf. When members of a pack are fractured and spread out, their companions will howl to provide a way of locating them. Think of it as nature’s GPS: By howling, dogs are able to communicate their respective locations to one another, even across long distances.

Since dogs really don’t know what a cop car is supposed to sound like, they’ll often interpret a siren as an animal’s howl. It’s also possible that dogs consider sirens to be a sign that something is abnormal in their environment, and that they want you, the pack leader, to be aware of it.

Contrary to belief, a dog is rarely howling because the noise hurts their delicate ears. If that were the case, some experts say, then they would display other behaviors, like running and hiding.

The more a dog hears and responds to a siren, the more they might be compelled to continue the behavior. That’s because dogs who howl and then notice the sound drifting away might begin to associate their vocalizing with the disappearance of the noise. In the future, they’ll probably recall that they “drove” the interloper away with their warbling and repeat the process.

While howling is usually harmless, sometimes it can be a sign that your pet is feeling separation anxiety from an owner or that they’re feeling unwell. If howling persists even without a screaming siren within earshot, you might consider taking them in for a check-up.

If you’ve wondered why dogs howl at sirens, now you know. It’s simply a way of signaling their location and not because it pains them. Owners, on the other hand, might feel differently.

Have you got a Big Question you'd like us to answer? If so, let us know by emailing us at bigquestions@mentalfloss.com.

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Animals
5 Ways to Keep Your Dog Calm on the Fourth of July

The Fourth of July can be rough for dogs. Fireworks displays light up their senses with unfamiliar noises, flashes, and smells, and parties flood their homes with strange guests who may invade the rooms they usually have as private retreats. And when distressed dogs escape, howl, or thrash around the house, Independence Day can quickly become a nightmare for their owners, too. To minimize Fido's stress this holiday, we spoke to some dog experts to discover the best ways to keep your canine calm on the Fourth of July.

1. EXERCISE

Anthony Newman, the dog whisperer who runs New York City's Calm Energy Dog Training, says that exercise is a great way to help your dog let off some nervous energy. “Whenever Fido is going to be neglected for an extended period of time, or around any stressful stimuli, it always helps to tire him out just before—and even during the night if you can,” Newman says. “As the saying goes, a tired dog is a good dog! He’ll be calmer, happier, and more peaceful.”

2. STAY INDOORS

Dr. Stephanie Liff, head veterinarian at Pure Paws Veterinary Care, says the best place to keep your pet during a fireworks show is inside and away from the windows. “If the pet is very scared, an escape-proof crate or a sound-insulated room, such as an internal bathroom, may help the pet to feel more secure,” Liff tells us. “If you cannot keep your pet inside, make sure that the pet is prevented from escape (monitor all exits and tell guests to monitor your pet).”

3. SOCIALIZE

While your dog may feel more secure in a room away from all the noise, Newman points out that keeping your dog isolated in another room for too long can be stressful for your pet. “Release his curiosity and let him in on the fun, to run around and play with both two-legged as well as four-legged guests,” Newman says. “Then back to his obedient room, bed, car, crate, or spot. Rinse and repeat as needed throughout the night."

4. TAKE CONTROL

According to Newman, the best way to keep your dog calm during the chaos of July 4th is to stay in charge. “If your dog winces, shivers, and runs away at loud noises, the last thing he wants is to feel like nobody else is looking out for him,” Newman says. Don’t let your dog run rampant around the house or follow him around trying to soothe him. Instead, Newman says it's important to “take control by attaching a super-light leash that you can grab and lead him whenever you need.”

5. MEDICATE

In extreme cases of nervousness, Liff says that you should talk to your vet about medication to sedate your dog.

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