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10 Questions Still Baffling Scientists

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Science has done a terrific job of answering some of the world’s most difficult questions, but certain mysteries still elude researchers. How does gravity work? Can your pet fish really predict an earthquake? Why do we yawn so much? Here’s what we don’t know and how close we are to figuring it out.

1. Why Do We Yawn?

Theories about why we yawn are as common as grumpy toddlers at nap time, but two explanations seem plausible after experimental tests. One is that yawns help cool the brain and optimize its performance. Psychologists at the State University of New York at Albany say it explains why we yawn when we’re drowsy: Like the fan in a computer, the yawn kicks in when our performance starts lagging.

But if yawns are our brains’ way of kick-starting their efficiency, why is yawning contagious? The brain-cooling camp suggests that it’s a way to maintain group vigilance and safety. When a member of a pack yawns, signaling that he is not functioning at his best, the whole group may need to yawn for a collective cognitive boost.

That’s not the only theory floating around, though. Another explanation contends that contagious yawning builds and maintains empathy between yawners. A sympathetic yawn signals an appreciation and understanding of someone else’s condition and subconsciously says, “Me too, buddy.” So which story is the accurate one? Scientists aren’t ready to declare a winner yet—they need a little time to sleep on it.

2. Why Do People Spontaneously Combust?

Here’s what we know: Humans really do spontaneously combust. One of the first people recorded to have gone up in smoke is a poor Italian knight who burst into flames after drinking strong wine in the mid–17th century. The cause of the mysterious fireworks befuddles scientists, but they’re certain that each instance is less spontaneous than it seems. Over centuries, 120 cases of spontaneous human combustion have been reported, but because most of the cases involve smokers, a common hypothesis is that an outside flame is involved. The theory is that a cigarette scorches the skin and breaks it deep enough to force body fat to seep rapidly from the wound into burning clothing; together they act like candle wax and a wick.

It’s far more probable than the competing idea—that methane gases build up in the intestines and are sparked from inside the body by a mix of enzymes. But there’s a problem with testing both theories: Researchers can’t just walk around setting people on fire. They may have found a substitute that will answer the question, though. Pig tissue combusts in a way that’s consistent with the “wick effect,” and samples are far easier to obtain. Who knew bacon would help solve the mystery of one of Spinal Tap’s drummers?

3. Why Do Placebos Work?

When a new drug enters clinical trials, researchers need a control group against which to compare its effects. Members of this group are given what they’re told is the drug but is actually a pill containing no active ingredients, a placebo. Frequently, though, the control subjects feel the drug’s effects. Or at least they say they do. What actually happens to placebo poppers is still unsettled. Some studies have found objectively measured effects that are in line with a real drug’s results. Others have found that the benefits are only subjective; patients said they felt better after taking the placebo, regardless of their actual improvement. This mixed bag of evidence could support any number of explanations. There could be an actual physiological response, Pavlovian conditioning (a patient expects to feel better after medicating), positive feelings from patient-doctor interactions, an unconscious desire to “do well” in a clinical trial, or even a natural improvement in symptoms.

Whatever the cause, pharmaceutical companies are keen to figure out the placebo effect given its potential to throw clinical trials into disarray. Real drugs often can’t compete against the effects of fakers, and about half get scrapped in late-stage trials. For the researchers who’ve spent nearly 10 years trying to bring their drugs to market, that’s a bitter pill to swallow.

4. What Was Life’s Last Universal Common Ancestor?

A whale and a bacterium or an octopus and an orchid don’t seem to have much in common, but deep down they’re all the same. Research reveals that most of life’s tiniest components, like proteins and nucleic acids, are nearly universal. The genetic code is written in the same way across all organisms. A small core of genome sequences is also similar across major branches of life’s family tree. All this suggests that every living thing made of cells can trace its lineage back to one source, a universal common ancestor.

In theory, this idea makes a lot of sense. Getting this ancestor to show up for a paternity test is tougher. Scientists estimate that the last universal common ancestor (LUCA) split into microbes and later eukaryotes (animals, plants, and the like) around 2.9 billion years ago. The fossil record from that era is scant, and by now, the genes that have traveled down the family tree have been lost, swapped, or shuffled around.

But some features of proteins and nucleic acids encoded by these genes—such as their three-dimensional structure—have been preserved throughout time. A survey of these molecular traits offers a glimpse at what the last universal common ancestor might have looked like. Researchers have found that tiny organelles (specialized subparts of cells) as well as their associated enzymes are shared by all major branches of life, meaning that they must have been present in the last universal common ancestor. This and other evidence suggests that the LUCA was as complex as a modern cell—which doesn’t make our forebear all that visually impressive. But on the plus side, until scientists get to the bottom of this question, we can all save money on Father’s Day cards for the granddaddy of all life on Earth.

5. How Does Memory Work?

For a long time, neuroscientists thought a memory was stored in a scattered group of neurons in either the hippocampus or in the neocortex. Last year, researchers at MIT proved that theory for the first time by causing mice to remember or forget an event by activating or deactivating the associated neurons.

It’s an essential piece to the puzzle, but to recall a memory on its own, the brain has to activate the correct assortment of neurons. And how exactly the brain pulls off that trick isn’t fully understood. Studies on rodents and brain imaging in people suggests that some of the same neurons that the original experience affected are involved. In other words, remembering something may not just be a matter of grabbing it from its storage space but re-forming the memory each time it’s pulled out.

6. Can Animals Really Predict Earthquakes?

The idea that our furry and feathered friends could warn us about impending doom is a nice one, but it’s been hard for scientists to prove. Pet owners have noted how their animals acted funny just before an earthquake since the days of ancient Greece. There’s no shortage of reports, but almost every one is anecdotal, based on opinions of what’s “normal” and “funny” for an animal. And the stories are generally reported long after the fact.

It’s not out of the question that animals may sense and react to some environmental change that we don’t notice—anything from seismic waves to changes in electric or magnetic fields. However, it’s not clear that earthquakes even produce such precursors. Plus, whatever the proposed cause, it’s nearly impossible to test. If we can’t predict earthquakes, we don’t know when to observe animals, and it’s even more difficult for researchers trying to reproduce the experiment later. The few “lucky” cases where quakes happened during animal experiments provide conflicting evidence. If you’re going to rely on a cat for earthquake advice, consult one with a degree in seismology.

7. How Do Organs Know When to Stop Growing?

Every mammal starts out as a single cell before growing into trillions of them. Usually, there’s tight control over the number and size of cells, tissue, and organs, but sometimes things go very wrong, resulting in anything from cancer to a leg that’s larger than its partner. So what’s sending the “stop growing” signal?

Four proteins that make up the core of what’s known as the Salvador-Warts-Hippo signaling pathway appear to help regulate growth for a number of organs. Shutoff signals sent down the pathway deactivate the protein that promotes growth, but that’s where scientists’ knowledge stops. Where these signals originate and which other elements are affecting SWH is unknown. Scientists continue to learn how to manipulate the pathway, discovering new triggers and working their way to the source, but there are still a lot of mysteries—including how we may be able to “turn off” cancer.

8. Are There Human Pheromones?

Can you actually smell someone’s fear? Or sniff out a rat? Plenty of animals communicate with chemical signals called pheromones, but whether humans are part of that club is a contentious issue. There’s some evidence of people making behavioral and physical changes in response to chemosignals, but scientists haven’t been able to figure out which chemicals trigger these responses. And despite what the labels on pheromone-infused colognes and hair gels will tell you, no compound has been identified as a human pheromone or linked to a specific response.

Moreover, if people are giving off pheromones, scientists aren’t sure how others are detecting them. Many mammals and reptiles have what’s known as a vomeronasal organ that detects pheromones. While some human noses contain the tiny organ, it may not be functional; sensory neurons have little or no connection with the nervous system. So for now, the answer to this question remains “maybe.” And that uncertainty truly stinks.

9. What’s the Deal With Gravity?

Of the four fundamental forces of nature, gravity is the runt of the litter. It holds the universe together, but it’s weaker than its three siblings: electromagnetism, weak nuclear forces, and strong nuclear forces. How much punier is it? The next step up, weak nuclear, is 10^26 (100,000,000,000,000,000,000, 000,000) times stronger. Gravity’s relatively feeble pull makes it hard to demonstrate with small objects in the lab.

Gravity doesn’t play well with the other forces either. Try as they might, scientists can’t use quantum theory and general relativity to explain gravity on small scales. And this incompatibility leaves us short of physicists’ grandest goal: a unified theory of everything.

Worse still, scientists can’t even figure out what gravity is made of. The other fundamental forces are all associated with particles that help carry them, but no one’s been able to detect the gravitational particle—the hypothetical graviton—even with the most super of supercolliders! And while some scientists are frustrated by its elusive nature, others know it’s just gravity’s way—the force has a reputation for bringing us down.

10. How Many Species Are There?

Taxonomists have been finding, naming, and describing species in an organized manner for more than 200 years, and they’re probably nowhere close to being finished. It’s not that they’re slacking off on the job either. In the last decade alone, scientists have reported more than 16,000 new species per year; in total, they’ve cataloged 1.2 million. It’s anybody’s guess how many are left undiscovered, though. Going out and finding every single species would take the 300,000 working taxonomists a lifetime, so they have to make educated guesses.

Making these kinds of extrapolations presents serious logistical hurdles. Biodiversity hotspots often fall in developing countries, which suffer from a shortage of taxonomists. Furthermore, up to 80 percent of the planet’s life may be hiding out in hard-to-reach places under the sea.

Given these troubles, it’s no wonder there’s a wide variance in expert guesses of how many species are left undiscovered. The most recent ballpark figures place the number between five and 15 million species, which makes the odds of someone discovering a unicorn just slightly better than we’d even dared to dream.

This story originally appeared in mental_floss magazine.

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iStock // Ekaterina Minaeva
Man Buys Two Metric Tons of LEGO Bricks; Sorts Them Via Machine Learning
May 21, 2017
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iStock // Ekaterina Minaeva

Jacques Mattheij made a small, but awesome, mistake. He went on eBay one evening and bid on a bunch of bulk LEGO brick auctions, then went to sleep. Upon waking, he discovered that he was the high bidder on many, and was now the proud owner of two tons of LEGO bricks. (This is about 4400 pounds.) He wrote, "[L]esson 1: if you win almost all bids you are bidding too high."

Mattheij had noticed that bulk, unsorted bricks sell for something like €10/kilogram, whereas sets are roughly €40/kg and rare parts go for up to €100/kg. Much of the value of the bricks is in their sorting. If he could reduce the entropy of these bins of unsorted bricks, he could make a tidy profit. While many people do this work by hand, the problem is enormous—just the kind of challenge for a computer. Mattheij writes:

There are 38000+ shapes and there are 100+ possible shades of color (you can roughly tell how old someone is by asking them what lego colors they remember from their youth).

In the following months, Mattheij built a proof-of-concept sorting system using, of course, LEGO. He broke the problem down into a series of sub-problems (including "feeding LEGO reliably from a hopper is surprisingly hard," one of those facts of nature that will stymie even the best system design). After tinkering with the prototype at length, he expanded the system to a surprisingly complex system of conveyer belts (powered by a home treadmill), various pieces of cabinetry, and "copious quantities of crazy glue."

Here's a video showing the current system running at low speed:

The key part of the system was running the bricks past a camera paired with a computer running a neural net-based image classifier. That allows the computer (when sufficiently trained on brick images) to recognize bricks and thus categorize them by color, shape, or other parameters. Remember that as bricks pass by, they can be in any orientation, can be dirty, can even be stuck to other pieces. So having a flexible software system is key to recognizing—in a fraction of a second—what a given brick is, in order to sort it out. When a match is found, a jet of compressed air pops the piece off the conveyer belt and into a waiting bin.

After much experimentation, Mattheij rewrote the software (several times in fact) to accomplish a variety of basic tasks. At its core, the system takes images from a webcam and feeds them to a neural network to do the classification. Of course, the neural net needs to be "trained" by showing it lots of images, and telling it what those images represent. Mattheij's breakthrough was allowing the machine to effectively train itself, with guidance: Running pieces through allows the system to take its own photos, make a guess, and build on that guess. As long as Mattheij corrects the incorrect guesses, he ends up with a decent (and self-reinforcing) corpus of training data. As the machine continues running, it can rack up more training, allowing it to recognize a broad variety of pieces on the fly.

Here's another video, focusing on how the pieces move on conveyer belts (running at slow speed so puny humans can follow). You can also see the air jets in action:

In an email interview, Mattheij told Mental Floss that the system currently sorts LEGO bricks into more than 50 categories. It can also be run in a color-sorting mode to bin the parts across 12 color groups. (Thus at present you'd likely do a two-pass sort on the bricks: once for shape, then a separate pass for color.) He continues to refine the system, with a focus on making its recognition abilities faster. At some point down the line, he plans to make the software portion open source. You're on your own as far as building conveyer belts, bins, and so forth.

Check out Mattheij's writeup in two parts for more information. It starts with an overview of the story, followed up with a deep dive on the software. He's also tweeting about the project (among other things). And if you look around a bit, you'll find bulk LEGO brick auctions online—it's definitely a thing!

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Sponsor Content: BarkBox
8 Common Dog Behaviors, Decoded
May 25, 2017
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Dogs are a lot more complicated than we give them credit for. As a result, sometimes things get lost in translation. We’ve yet to invent a dog-to-English translator, but there are certain behaviors you can learn to read in order to better understand what your dog is trying to tell you. The more tuned-in you are to your dog’s emotions, the better you’ll be able to respond—whether that means giving her some space or welcoming a wet, slobbery kiss. 

1. What you’ll see: Your dog is standing with his legs and body relaxed and tail low. His ears are up, but not pointed forward. His mouth is slightly open, he’s panting lightly, and his tongue is loose. His eyes? Soft or maybe slightly squinty from getting his smile on.

What it means: “Hey there, friend!” Your pup is in a calm, relaxed state. He’s open to mingling, which means you can feel comfortable letting friends say hi.

2. What you’ll see: Your dog is standing with her body leaning forward. Her ears are erect and angled forward—or have at least perked up if they’re floppy—and her mouth is closed. Her tail might be sticking out horizontally or sticking straight up and wagging slightly.

What it means: “Hark! Who goes there?!” Something caught your pup’s attention and now she’s on high alert, trying to discern whether or not the person, animal, or situation is a threat. She’ll likely stay on guard until she feels safe or becomes distracted.

3. What you’ll see: Your dog is standing, leaning slightly forward. His body and legs are tense, and his hackles—those hairs along his back and neck—are raised. His tail is stiff and twitching, not swooping playfully. His mouth is open, teeth are exposed, and he may be snarling, snapping, or barking excessively.

What it means: “Don’t mess with me!” This dog is asserting his social dominance and letting others know that he might attack if they don’t defer accordingly. A dog in this stance could be either offensively aggressive or defensively aggressive. If you encounter a dog in this state, play it safe and back away slowly without making eye contact.

4. What you’ll see: As another dog approaches, your dog lies down on his back with his tail tucked in between his legs. His paws are tucked in too, his ears are flat, and he isn’t making direct eye contact with the other dog standing over him.

What it means: “I come in peace!” Your pooch is displaying signs of submission to a more dominant dog, conveying total surrender to avoid physical confrontation. Other, less obvious, signs of submission include ears that are flattened back against the head, an avoidance of eye contact, a tongue flick, and bared teeth. Yup—a dog might bare his teeth while still being submissive, but they’ll likely be clenched together, the lips opened horizontally rather than curled up to show the front canines. A submissive dog will also slink backward or inward rather than forward, which would indicate more aggressive behavior.

5. What you’ll see: Your dog is crouching with her back hunched, tail tucked, and the corner of her mouth pulled back with lips slightly curled. Her shoulders, or hackles, are raised and her ears are flattened. She’s avoiding eye contact.

What it means: “I’m scared, but will fight you if I have to.” This dog’s fight or flight instincts have been activated. It’s best to keep your distance from a dog in this emotional state because she could attack if she feels cornered.

6. What you’ll see: You’re staring at your dog, holding eye contact. Your dog looks away from you, tentatively looks back, then looks away again. After some time, he licks his chops and yawns.

What it means: “I don’t know what’s going on and it’s weirding me out.” Your dog doesn’t know what to make of the situation, but rather than nipping or barking, he’ll stick to behaviors he knows are OK, like yawning, licking his chops, or shaking as if he’s wet. You’ll want to intervene by removing whatever it is causing him discomfort—such as an overly grabby child—and giving him some space to relax.

7. What you’ll see: Your dog has her front paws bent and lowered onto the ground with her rear in the air. Her body is relaxed, loose, and wiggly, and her tail is up and wagging from side to side. She might also let out a high-pitched or impatient bark.

What it means: “What’s the hold up? Let’s play!” This classic stance, known to dog trainers and behaviorists as “the play bow,” is a sign she’s ready to let the good times roll. Get ready for a round of fetch or tug of war, or for a good long outing at the dog park.

8. What you’ll see: You’ve just gotten home from work and your dog rushes over. He can’t stop wiggling his backside, and he may even lower himself into a giant stretch, like he’s doing yoga.

What it means: “OhmygoshImsohappytoseeyou I love you so much you’re my best friend foreverandeverandever!!!!” This one’s easy: Your pup is overjoyed his BFF is back. That big stretch is something dogs don’t pull out for just anyone; they save that for the people they truly love. Show him you feel the same way with a good belly rub and a handful of his favorite treats.

The best way to say “I love you” in dog? A monthly subscription to BarkBox. Your favorite pup will get a package filled with treats, toys, and other good stuff (and in return, you’ll probably get lots of sloppy kisses). Visit BarkBox to learn more.