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What’s the Difference Between Hair and Fur?

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The most common distinction between hair and fur that people tend to make is usually between you and your pet. You have hair on your head, and your dog Fido has fur all over its body. Easy enough, right?

Well, actually, it's kind of complicated. "The way I think a lot of people understand fur versus hair is in the density of follicles," says Ross McPhee, Curator of the Department of Mammalogy at the American Museum of Natural History. "So for fur-bearing animals—which were converted into coats and so-forth—people always wanted it to be something that was very dense, so there’s the idea therefore that fur is dense, and it certainly is in [the] kinds of fur-bearers that we use for this purpose. Whereas hair is not so dense. There's less of it." The reason this distinction doesn’t work, however, is that humans have a similar follicle density to any other ape, and an adult scalp has the same follicle density as a mouse

Chemically, it's all keratin—the same protein substance that also makes up skin, feathers, nails, hoofs, claws, and horns—that grows on mammals (either all over or just in certain places). So, MacPhee says, "fundamentally, they are all the same thing. Naturally, there’s specialization, just as there are in tissues all over the body."

There are three main types of hair: ground hair, guard hair, and whiskers. Two of them, ground and guard, are classified as fur. Ground hair is used primarily as insulation and is soft, while guard hair is for protection from the elements and tends to be coarse. Because it's in-between ground and guard, human hair can be reasonably called fur.

No matter how human hair is classified, however, the distinction between hair and fur shows up in the third category: whiskers.

Whiskers, although hair, are categorically not fur. Whiskers have a few differences, including that they tend to be longer and stiffer (but this is not always the case), and they're important sensory organs. "Every follicle has a certain amount of innervation," MacPhee explains. The way it works for whiskers is that they have mechanoreceptors, which means that when the whisker is disturbed by hitting an object, a signal is immediately sent back to the brain and analyzed there. Which is why whiskers are utilized by all kinds of mammals as a sensory apparatus in their environment. A manatee's face [PDF], for instance, is exclusively whiskers because every follicle has these key (and distinct) features. These types of whiskers are known as vibrissae—and humans don't have them. "The whiskers that you find on a male are just hair," MacPhee says. "They’re not richly endowed with these sensory nerves. Whether they’re on the muzzle, or the eyebrows, or on other places on the body. Very frequently, mammals have vibrissae on their wrists and ankles. Although cats and dogs have good vision, it’s clear they’ve retained vibrissae and some degree of information to fine tune their body."

Ultimately, though, it might just be a word thing. "I’m not sure that the hair versus fur distinction is always made in other languages," MacPhee says. "Humans universally only have hair, right? Not fur, even though there is no important way to distinguish the two. The differences are arbitrary."

THE GROWTH MYTH

“Wait a second!” you scream before you admit that you have fur on you. “I thought the common difference is that hair keeps growing while fur has a set length at which it stops!” That's not true: Human hair doesn’t keep growing and growing. All hair—whether it’s on your human head and arms or on the body of a chimpanzee or on beloved Fido—has a growth limit based on genetics, so your shorthaired cat will stay shorthaired even if you don’t get its fur trimmed.

The myth of the difference between hair and fur is perpetuated by a misunderstanding of the hair growth cycle in the body that regulates hair length. The “anagen” period of the cycle is the phase of constant hair growth; the “catagen” phase is a transitional time when the body tells the hair to begin to stop growing, shrinking the strands themselves and cutting the roots of the hairs so new strands won’t be produced; and the “telogen” phase is when the hair follicle rests and no new growth occurs. This leads to the “exogen” phase, in which the hair falls out to start the cycle over again.

So in humans, hair will stop growing after the cycle runs through each phase. It’s just that the cycle in you as a human is longer than, say, Fido’s hair growth cycle. The anagen period of active growth on a human scalp could run anywhere from 2 to 7 years (taking into consideration other factors such as baldness), while the telogen period in which the hair on your scalp is dormant could go up to 100 days.

The cycle itself is relative not only to different species, but also to different areas of the body, which explains why the hair on your arms and legs isn’t the same length as the hair on your head. For instance, the same 2- to 7-year anagen phase on your head lasts 30 to 45 days on your arms and legs.

On animals, the hair all seems to be a fixed length to us because their cycle is relatively shorter when compared to ours, and so the mistake of differentiating fur from hair is made. It becomes clearer when you consider that longer haired dogs just have a longer period of hair growth than something like a Lab, which has a shorter cycle.

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Do 'Close Door' Buttons in Elevators Actually Do Anything?
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When you’re running late for work, one small comfort is finding an empty elevator waiting for you at your office building. You scurry inside, and since no one else is waiting to enter, you jab the 'close door' button. The doors comply, the elevator starts moving, and you breathe a sigh of relief.

This is a familiar scenario for many, but it’s also a big fat lie. That’s because most of the door-close buttons in U.S. elevators don’t actually work. In fact, they’re programmed that way.

But before you get ready to send off a strongly worded email to your office building’s elevator manufacturer, you may want to hear why this is the case. When the Americans With Disabilities Act was first passed in 1990, certain requirements for elevators were outlined, such as the installation of raised buttons, braille signs, and audible signals.

The act ensured that someone with a disability would have enough time to get inside, stipulating that elevator doors must remain fully open for at least three seconds and thereby preventing the button from cutting that time short. Some elevator manufacturers took it one step further by deactivating the button entirely.

Since the life span of an elevator is about 25 years and the Disabilities Act has been around for 28 years, it’s safe to assume that most of the elevators in operation today do not have a functioning 'close door' button, The New York Times reports. Only firefighters are able to close elevator doors manually through the use of a key.

It's important to note that there are exceptions to this rule, though. As the New York Daily News noted, New York City elevators are required by law to have working 'close door' buttons, even though some operate on a long delay (so long, in fact, that it calls the button's usefulness into question).

However, you’re in luck if you’re taking a lift (which, of course, is British for “elevator”). 'Close door' buttons are fully functional in most elevators in the UK, according to The Telegraph. A spokesman for the Lift and Escalator Industry Association told the newspaper that not all elevators have the button, but when they’re present, they do work. Again, the time it takes for the doors to shut after pressing the button varies from lift to lift.

While U.S. elevator manufacturers have a seemingly good reason for disabling the 'close door' button, some may question the point of propagating the myth and installing a button that serves no purpose in the first place. In response, some would argue that placebo buttons serve an important psychological function in society.

"Perceived control is very important," Harvard psychologist Ellen J. Langer told The New York Times. "It diminishes stress and promotes well-being."

That’s right: By believing that you’re in control of your fate—or at least how quickly you can make it up to the sixth floor—you’re better off. It doesn’t end with elevators, either. Buttons placed at city crosswalks are often disabled, and the thermostats in many office buildings are rigged so that the temperature can’t be altered (even if the numbers appear to change).

Some might swear up and down that elevator 'close door' buttons work, but this, too, could be your brain deceiving you. As author David McRaney wrote in an essay: “If you happen to find yourself pressing a nonfunctional close-door button, and later the doors close, you’ll probably never notice because a little spurt of happiness will cascade through your brain once you see what you believe is a response to your action. Your behavior was just reinforced. You will keep pressing the button in the future.”

According to The New Yorker, these buttons are designed to alleviate some of the subconscious anxiety that comes from stepping inside a tiny box that's hoisted up some 20 or 40 or 80 floors by a cable: “Elevator design is rooted in deception—to disguise not only the bare fact of the box hanging by ropes but also the tethering of tenants to a system over which they have no command."

So now you know: Next time you’re running late to work, take comfort in the fact that those few extra seconds you would’ve saved by pressing a functioning 'close door' button aren’t worth all that much in the long run.

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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What’s the Difference Between Prison and Jail?
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Many people use the terms jail and prison interchangeably, and while both terms refer to areas where people are held, there's a substantial difference between the two methods of incarceration. Where a person who is accused of a crime is held, and for how long, is a factor in determining the difference between the two—and whether a person is held in a jail or a prison is largely determined by the severity of the crime they have committed.

A jail (or, for our British friends, a gaol) refers to a small, temporary holding facility—run by local governments and supervised by county sheriff departments—that is designed to detain recently arrested people who have committed a minor offense or misdemeanor. A person can also be held in jail for an extended period of time if the sentence for their offense is less than a year. There are currently 3163 local jail facilities in the United States.

A jail is different from the similarly temporary “lockup”—sort of like “pre-jail”—which is located in local police departments and holds offenders unable to post bail, people arrested for public drunkenness who are kept until they are sober, or, most importantly, offenders waiting to be processed into the jail system.

A prison, on the other hand, is usually a large state- or federal-run facility meant to house people convicted of a serious crime or felony, and whose sentences for those crimes surpass 365 days. A prison could also be called a “penitentiary,” among other names.

To be put in a state prison, a person must be convicted of breaking a state law. To be put in a federal prison, a person must be convicted of breaking federal law. Basic amenities in a prison are more extensive than in a jail because, obviously, an inmate is likely to spend more than a year of his or her life confined inside a prison. As of 2012, there were 4575 operating prisons in the U.S.—the most in the world. The country with the second highest number of operating prisons is Russia, which has just 1029 facilities.

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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