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Why Do We Have Fingerprints?

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Though fingerprints are handy for identifying perps, biologically, scientists still aren't quite sure what our fingerprints are for. But as they test different hypotheses, they're getting closer to the answer—and learning some pretty cool stuff in the process.

Is it to improve our sense of touch?

In a 2009 study, researchers from the Ecole Normale Superieure in Paris built two biomimetic tactile sensors, which mimic the human ability to touch and perceive texture. One had grooves that mimicked fingerprints; the other was flat like smooth skin. When these faux fingers moved across roughly-textured surfaces, the fingerprinted sensors produced vibrations up to 100 times stronger than the smooth ones. These vibrations, the scientists found, were dominated by a frequency in the optimal range of sensitivity of the Pacinian corpuscles, receptors in our skin that detect pressure changes and vibrations. These researchers think that our fingerprints' job might be to amplify certain tactile information so that it's more easily processed by the nervous system. They also suggest that the swirling patterns of fingerprints ensure that some of the ridges are always brushing sideways across a surface, no matter which way the finger is moving, to better generate vibrations.

Is it to improve our grip?

Humans, apes, monkeys and koalas all have fingerprints. Some New World monkeys even have ridged pads on their tree-gripping tails. Fingerprints’ design, and their presence in all these animals, has led people to think that they’re an adaptation for improved grip while climbing trees and manipulating objects, but there isn’t much experimental evidence for that. Research by biomechanicists at the University of Manchester, who tested the idea in 2009, suggests that a good grip isn’t fingerprints’ forte. Dr. Roland Ennos and his student Peter Warman tested the grip of Warman's fingers at different angles on strips of acrylic glass sheets similar to Plexiglas. While many solid objects obey Amonton's law and friction between them is proportional to the force between them, the friction between finger and glass increased less than Ennos expected when more pressure was applied. The pair inked Warman's fingers to measure the contact area between them and the sheets and found that friction did increase when the contact area increased, but also noted that the grooves between fingerprint ridges reduce the fingers' contact surface with the glass by about one third, compared with smooth skin, and actually reduced friction and ability to grip.

What are some other possibilities?

Ennos and Warman throw out a few other plausible explanations for fingerprints at the end of their paper: that they allow our skin more to more easily comply with and deform to objects we're touching or holding, reducing shear stress and preventing blister formation; that they increase friction on rough surfaces compared with flat skin because the ridges project into the depressions on these surfaces and provide a higher contact area; that they facilitate runoff of water like tire treads. Ennos says his lab is testing all of these hypotheses, but hasn’t published any results yet.

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Big Questions
Do Cats Fart?
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Certain philosophical questions can invade even the most disciplined of minds. Do aliens exist? Can a soul ever be measured? Do cats fart?

While the latter may not have weighed heavily on some of history’s great brains, it’s certainly no less deserving of an answer. And in contrast to existential queries, there’s a pretty definitive response: Yes, they do. We just don’t really hear it.

According to veterinarians who have realized their job sometimes involves answering inane questions about animals passing gas, cats have all the biological hardware necessary for a fart: a gastrointestinal system and an anus. When excess air builds up as a result of gulping breaths or gut bacteria, a pungent cloud will be released from their rear ends. Smell a kitten’s butt sometime and you’ll walk away convinced that cats fart.

The discretion, or lack of audible farts, is probably due to the fact that cats don’t gulp their food like dogs do, leading to less air accumulating in their digestive tract.

So, yes, cats do fart. But they do it with the same grace and stealth they use to approach everything else. Think about that the next time you blame the dog.

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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Big Questions
What Are the Northern Lights?
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Over the centuries, many have gazed up at one of the Earth’s most fascinatingly beautiful natural wonders: the Northern Lights. In the past couple of weeks, some lucky American stargazers have gotten the chance to see them from their very own backyards—and could again this week, according to Thrillist. But what are they?

Before science was able to get a read on what exactly was happening in the night sky, ancient tribes had their own theories for what caused the jaw-dropping light show. Many early beliefs had roots in religion, such as that the light was a pathway souls traveled to reach heaven (Eskimo tribes) or that the light was an eternal battle of dead warriors (Middle-Age Europe). Early researchers were a bit more reasonable in their approximations, and most surrounded the idea of the reflection of sunlight off the ice caps. In 1619, Galileo Galilei named the lights the aurora borealis after Aurora, the Roman goddess of morning, after concluding they were a product of sunlight reflecting from the atmosphere.

Today, scientists have come to the general agreement that the lights are caused by the collision of electrically charged solar particles and atoms from our atmosphere. The energy from the collisions is released as light, and the reason it happens around the poles is because that's where the Earth’s magnetic field is the strongest. In 2008, a team at UCLA concluded that “when two magnetic field lines come close together due to the storage of energy from the sun, a critical limit is reached and the magnetic field lines reconnect, causing magnetic energy to be transformed into kinetic energy and heat. Energy is released, and the plasma is accelerated, producing accelerated electrons.”

"Our data show clearly and for the first time that magnetic reconnection is the trigger," said Vassilis Angelopoulos, a UCLA professor of Earth and Space Sciences. "Reconnection results in a slingshot acceleration of waves and plasma along magnetic field lines, lighting up the aurora underneath even before the near-Earth space has had a chance to respond. We are providing the evidence that this is happening."

The best time to see the Northern Lights is during the winter, due to the Earth’s position in relation to the sun (shorter days means darker night skies). And by the way, it’s not just the North Pole that puts on a show—there are Southern Lights, too. There are also aurora borealis on other planets—including Mars—so rest assured that future generations born “abroad” will not miss out on this spectacular feat of nature.

Haven’t seen them yet? Traditionally, the best places to catch a glimpse of the Northern Lights are in Iceland, Sweden, Norway, Finland, Greenland, northern Canada, and Alaska. Maybe you'll get lucky this week and sneak a peek from your very own window. Check out Aurorasaurus for regular updates on where they are showing.

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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