12 Common Things Science Still Hasn't Figured Out

Laughter: Still a scientific mystery
Laughter: Still a scientific mystery

We’ve learned enough about physics to send humans to the Moon. We’ve discovered that DNA carries our genetic information. Scientists have even gotten closer to solving the mystery of whether cats can behave as both solids and liquids [PDF].

But there are still some basic questions we haven’t answered, including these frustratingly persistent scientific mysteries.

1. Why We Cry

Some of us tear up watching a sad movie; sometimes, we're so happy that we burst into tears. But according to science, crying in response to intense emotions doesn’t seem to be a useful behavior, and it might not have a biological purpose.

What science does know is that not all tears are created equal. The chemical composition of the tears produced when we cry, which are called psychic tears, is slightly different from the composition of the tears that lubricate and help expel foreign bodies from the eyes. This has led some to theorize that the chemical makeup of psychic tears makes them emotionally healing. But evidence showing that the chemical differences have substantial psychological effects—let alone that such effects explain why crying evolved—is lacking.

And that’s not where the theories end. Some evolutionary psychologists think that crying may have evolved as a distress call that brings help: In a 2009 paper, one researcher suggested that tears may signal submission and helplessness by blurring vision, which prompts others to aid (or at least not harm) the crier. But other researchers have pointed out that we often cry after a stressful situation has resolved, not while it’s in progress and we need to signal for help; it’s also typical for people to avoid crying publicly and to look unfavorably on those who do. In any case, these hypotheses, like most in evolutionary psychology, are difficult to test.

2. How to Cure Hiccups

Maybe you hold your breath. Maybe you chug water. Unfortunately, nothing has been found to reliably eliminate hiccups, despite the overwhelming number of folk remedies on the internet. This sad state of affairs is likely due to insufficient research: Serious cases of the hiccups are rare, and the mild cases are brief and don’t usually cause problems.

Most of the treatments for severe cases of hiccups—doses of sedating antipsychotics like haloperidol, vagus nerve stimulation, digital rectal massage—aren’t exactly things you could try on your own. For now, you’ll have to endure hiccups or stick with unproven, but usually harmless, solutions. At least they give you an excuse to eat peanut butter by the spoonful.

3. How General Anesthesia Works

As you’re rolling into surgery, you probably assume that your doctors not only know how to perform the procedure, but understand how the drugs that knock you out actually do so. But you’d be wrong. Scientists do know that local anesthetics like Novocain block pain signals before they reach the central nervous system by altering the function of specific proteins on nerve cells. But the molecular basis of general anesthesia is more of a mystery. These drugs seem to interfere with the functions of a variety of proteins on nerve cells in the central nervous system, but how they accomplish this is not well understood. General anesthetics come in a variety of types, and they likely don’t all work the same way, so developing models of how the compounds work on the molecular level may continue to be a challenge.

4. How Tylenol Kills Pain

A layperson taking Tylenol to relieve pain might think it works like non-steroidal anti-inflammatory drugs (NSAIDs), such as ibuprofen and aspirin, which block some enzymes and, in turn, the pain- and inflammation-causing chemicals they produce. But that’s not the case—acetaminophen, the active ingredient in Tylenol, seems to need specific chemical conditions to work on those enzymes, and it doesn’t appear to reduce inflammation as the NSAIDs do.

Some researchers think acetaminophen may alter the way pain is perceived by interacting with certain proteins on nerve cells, possibly including serotonin receptors, cannabinoid receptors, opioid receptors, and specific channels on nerves in the spinal cord that transmit pain and itch signals. Acetaminophen byproducts have also been shown to activate these channels rather than shutting them down, further complicating the question.

5. Why We Sleep

Too little sleep impairs thinking in the short term and increases the risk of several serious diseases in the long term, while complete sleep deprivation is fatal. We may have evolved to sleep because it aids healing, memory consolidation, and other important processes, but we still have much to learn about the ways sleeping achieves these ends. Other roles for sleep, like conserving energy during times when it wouldn’t be advantageous to be awake (for example, during scorching-hot days in Death Valley) have been proposed as well.

At least for now, we don’t have a single, conclusive answer to the question of why we sleep. But no matter how sleeping arose, we can probably accept that it provided a substantial evolutionary advantage once in place, since sleep is found across much of the animal kingdom.

6. Why Only Some Thunderstorms Produce Tornadoes

A standard explanation of how tornadoes form is that they’re spawned when cold, dry air mingles with warm, humid air—that’s how we justify the fact that Tornado Alley in the central United States, where Arctic air, air from the Southwest, and air from the Gulf of Mexico mix, has so many tornadoes. But that’s not the whole story. These conditions do create more thunderstorms, but not all thunderstorms include tornadoes, and scientists aren’t sure why.

In some cases, tornadoes may form is when there are temperature changes in the air flowing downward around mesocyclones (vortexes within the types of storms tornadoes can come from). This idea has theoretical and experimental support, but even without these temperature variations, tornadoes can still form, demonstrating how much more we have to learn about the phenomenon.

7. Why We Itch

At a basic level, itch is an unpleasant sensation that triggers the urge to scratch. Scratching could end up making an itch worse, but it may also serve a purpose. Mechanical itch—the kind triggered when fine hairs on your body are disturbed—may alert you to the presence of biting insects or parasites, and scratching could brush them away.

This hypothesis is difficult to test, and it doesn’t cover chemical itch caused by histamine and other scratch-provoking substances. Long after you’ve missed your chance to brush a mosquito off your skin, histamine in the itchy bump it has left behind continues to compel you to scratch. Whether this type of itching serves a purpose, or is simply an incidental activation of the itch system, isn’t conclusively known.

8. How We Age

Despite what many beauty experts claim, no one really has aging figured out. Reactive chemicals called free radicals are often blamed, but they’re not the sole cause of aging, and our cells have numerous ways to help keep damage caused by excess free radicals to a minimum. Shortening of the telomeres, the protective caps of DNA at the ends of each chromosome, is another frequently cited cause of aging—but it’s not the only factor. Numerous other contributors to aging have been discovered, but no single factor explains all or even most of the aging process, making this a difficult question to answer.

9. Why We Laugh

Laughter, like crying, may have developed as a social tool. Laughter doesn't appear to be a uniquely human behavior, and it may not even be limited to primates. Rats produce laughter when tickled, for example, and many other social animals, such as dolphins [PDF], make specific sounds associated with play-fighting that have been likened to laughter.

A leading hypothesis for why we laugh is that laughter promotes pro-social behavior by letting playmates know that the fighting is just a game. But even if our interpretations of these behaviors are correct, it’s possible that humans evolved different uses for laughter after our evolutionary splits with other animal species, making the reason for human laughter another open question.

10. How and Why Animals Migrate Back to Their Birthplaces

Some animals migrate to the sites of their birth to mate—a practice known as natal philopatry—with stunning precision. Female Antarctic fur seals, for example, can return to within one body length of their exact birthplaces to breed.

But how do they get there after months or years away? One possibility is that some migratory animals navigate by sensing variations in Earth’s geomagnetic field. While this makes sense given that some migratory animals, such as sea turtles, are known to be highly sensitive to these variations, it has not been conclusively demonstrated that they navigate this way.

Other creatures, such as Pacific salmon, may use smell to direct them toward their breeding grounds. These fish have been shown experimentally to be able to home in on chemical cues from the water in which they developed into adults. But these chemical breadcrumbs wouldn’t be detectable across the vast ocean, meaning that even if the salmon use them to navigate, they must also have a way to direct themselves close enough to the source to smell them. The complete mechanisms behind natal philopatry, even in this well-studied case, are still unknown.

11. What Dreams are For

If the question of why we sleep is complicated, the question of why we dream is even more so. Dreaming—especially with vivid, fanciful dreams—is most correlated with rapid eye movement (REM) sleep, which itself is poorly understood. One thought is that dreaming evolved to help us sort out or rehearse solutions to problems in our waking lives, but there is no hard evidence that this is the case.

Although our dreams may feel significant to us, it’s also possible that they serve no purpose—they may simply be a byproduct of other processes that occur during REM sleep. Studying the neurological basis of the strange and highly subjective experience of dreaming is complicated, which is why understanding the origin of dreaming is still beyond our grasp.

12. How Turbulence Happens

Understanding how turbulence works is incredibly important from an engineering perspective, since it affects everything from how internal combustion engines work to how far golf balls can travel. And now that most of classical physics (encompassing the laws of mechanics, thermodynamics, and so on) has long been established, turbulence is considered one of the biggest remaining problems in the field. No one has figured out a way to perfectly model turbulent flow.

Modeling turbulence requires the Navier–Stokes equations, which describe the motion of fluids (liquids, gases, and plasmas). And that’s the main problem: These equations themselves are poorly understood—so much so that producing a proof about one of their basic properties is one of the seven Millennium Prize Problems. It’s considered one of the most important open classic questions in math—and there's a million dollars waiting for anyone who can figure it out.

12 Facts About Diabetes Mellitus


Thirty million Americans—about 9 percent of the country's population—are living with diabetes mellitus, or simply diabetes. This chronic condition is characterized by sustained high blood sugar levels. In many patients, symptoms can be managed with insulin injections and lifestyle changes, but in others, the complications can be deadly. Here's what you need to know about diabetes mellitus.

1. There are three types of diabetes.

In healthy people, the pancreas produces enough of the hormone insulin to metabolize sugars into glucose and move the glucose into cells, where it's used for energy.

But people with type 2 diabetes—the most common form of the disease, accounting for about 95 percent of cases—either can't produce enough insulin to transport the sugars, or their cells have become insulin-resistant. The result is a buildup of glucose in the blood (a.k.a. high blood sugar or hyperglycemia). Type 2 diabetes typically develops in adults.

Type 1 diabetes, also known as juvenile diabetes, makes up the remaining 5 percent of chronic cases and most often develops in children and young adults. With this condition, the initial problem isn’t blood sugar levels, but insulin production: The pancreas can’t make enough insulin to process even normal amounts of glucose. The sugar builds up as a result, leading to dangerous concentrations in the bloodstream.

The third form, gestational diabetes, only afflicts pregnant people who weren’t diabetic before their pregnancy. The mother's blood glucose levels usually spike around the 24th week of pregnancy, but with a healthy diet, exercise, and insulin shots in some cases, diabetes symptoms usually can be managed. Blood sugar levels tend to return to normal in patients following their pregnancies.

2. The mellitus in diabetes mellitus means "honey sweet."

Around 3000 years ago, ancient Egyptians described a condition with diabetes-like symptoms, though it wasn't called diabetes yet. It took a few hundred years before the Greek physician Araetus of Cappodocia came up with the name diabetes based on the Greek word for "passing through" (as in passing a lot of urine, a common diabetes symptom). English doctor Thomas Willis tacked on the word mellitus, meaning "honey sweet," in 1675, building on previous physicians' observations that diabetic patients had sweet urine. Finally, in 1776, another English physician named Matthew Dobson confirmed that both the blood and urine of diabetes patients were made sweeter by high levels of glucose in their blood.

3. The cause of one type of diabetes is well understood; the other, not so much.

A person’s lifestyle is a key predictor of developing type 2 diabetes. Factors like being overweight or obese, consuming a high-calorie diet, smoking, and seldom exercising contribute to the risk. Foods and drinks that are high in sugar—soda, candy, ice cream, dessert— may contribute to hyperglycemia, but any food that’s high in calories, even if it's not sweet, can raise blood sugar levels.

In contrast to these well-established factors, medical experts aren’t entirely sure what causes type 1 diabetes. We do know that type 1 is an autoimmune disease that develops when the body attacks and damages insulin-producing cells in the pancreas. Some scientists think that environmental factors, like viruses, may trigger this immune response.

4. Family history also plays a role in diabetes risk.

If a parent or sibling has type 2 diabetes, you are predisposed to developing pre-diabetes and type 2 diabetes. Lifestyle habits explain some of these incidences, since family members may share similar diets and exercise habits. Genetics also play a role, but just because one close relative has diabetes does not mean you're destined to. Research conducted on identical twins, which share identical genes, showed that the pairs have discordant risk. Among twins in which one has type 1 diabetes, the other has only a 50 percent chance of developing it; for type 2, the risk for the second twin is 75 percent at most.

5. Racial minorities are at a higher risk for developing diabetes.

Many racial minority groups in the U.S. have a higher chance of developing type 2 diabetes. Black Americans, Latino Americans, Native Americans, Pacific Islanders, and some groups of Asian Americans are more likely to have pre-diabetes and type 2 diabetes than white Americans. This can be partly explained by the fact that some of these groups also have higher rates of obesity, which is one of the primary risk factors of type 2 diabetes. Socioeconomics may also play a role: One study shows that people with diabetes living in poverty are less likely to visit diabetes clinics and receive proper testing than their middle-income counterparts. According to another study, diabetic people without health insurance have higher blood sugar, blood pressure, and cholesterol rates than insured diabetics. Genetics, on the other hand, don’t appear to contribute to these trends.

6. Diabetes is one of the world's deadliest diseases.

With proper management, people with diabetes can live long, comfortable lives. But if the disease isn’t treated, it can have dire consequences. Diabetics make up the majority of people who develop chronic kidney disease, have adult-onset blindness, and need lower-limb amputations. In the most serious cases, diabetes leads to death. The condition is one of the deadliest diseases in the world, killing more people than breast cancer and AIDS combined.

7. Millions of Americans are pre-diabetic.

According to the CDC, 84 million adults living in the U.S. are pre-diabetic: Their blood sugar is higher than what’s considered safe, but hasn't yet reached diabetic level. In pre-diabetic patients, blood glucose levels after eight hours of fasting fall between 100 and 125 milligrams per deciliter, and diabetic levels are anything above that. People with pre-diabetes are not just at a greater risk for type 2 diabetes, but also for heart disease and stroke. Fortunately, people who are diagnosed with pre-diabetes can take steps to eat a healthier diet, increase physical activity, and test their blood glucose level several times a day to control the condition. In some cases, doctors will prescribe drugs like metformin that make the body more receptive to the insulin it produces.

8. After climbing for decades, rates of diabetes incidence are declining.

In the U.S., the rate of new diagnoses skyrocketed 382 percent between 1988 and 2014. Globally, 108 million people had diabetes in 1980, but by 2014 that number was 422 million.

But thanks to nationwide education and prevention efforts, the trend has reversed in the U.S., according to the CDC. Since peaking in 2009, the number of new diabetes cases in America has dropped by 35 percent. In that same timeframe, the number of people living with diagnosed diabetes in the U.S. has plateaued, suggesting people with the condition are living longer.

9. The first successful treatment for type 1 diabetes occurred in 1922.

Prior to the 20th century, type 1 diabetes was usually fatal. Diabetic ketoacidosis—a toxic buildup of chemicals called ketones, which arise when the body can no longer use glucose and instead breaks down other tissues for energy—killed most patients within a year or two of diagnosis. In searching for way to save children with juvenile (type 1) diabetes, Canadian physician Frederick Banting and medical student Charles Best built on the work of earlier researchers, who had demonstrated that removing the pancreas from a dog immediately caused diabetes symptoms in the animal. Banting and Best extracted insulin from dog pancreases in University of Toronto professor J.J.R. Macleod's lab. After injecting the insulin back into dogs whose pancreases had been removed, they realized the hormone regulated blood sugar levels. On January 11, 1922, they administered insulin to a human patient, and further refined the extract to reduce side effects. In 1923, Banting and Macleod received the Nobel Prize in Medicine for their work.

10. A pioneering physicist discovered the difference between type and and type 1 diabetes.

In the 1950s, physicist Rosalyn Yalow and her research partner Solomon Berson developed a method for measuring minute amounts of substances in blood. Inspired by Yalow's husband's struggle with diabetes, Yalow focused her research on insulin. Their "radioimmunoassay" technology revealed that some diabetes patients were still able to produce their own insulin, leading them to create two separate categories for the disease: “insulin-dependent” (type 1) and “non-insulin-dependent” (type 2). Prior to that discovery in 1959, there was no distinction between the two types. In 1977, Yalow won the 1977 Nobel Prize in Medicine for the radioimmunoassay, one of only 12 female Nobel laureates in medicine.

11. Making one insulin dose once required tons of pig parts.

Insulin is relatively easy to make today. Most of what's used in injections comes from a special non-disease-producing laboratory strain of E. coli bacteria that's been genetically modified to produce insulin, but that wasn't always the case. Until about 40 years ago, 2 tons of pig pancreases were required to produce just 8 ounces of pure insulin. The pig parts were typically recycled from pork farms.

12. A quarter of diabetes patients don’t know they have it.

The symptoms of type 2 diabetes can develop for years before patients think to ask their doctor about them. These include frequent urination, unexplained thirst, numbness in the extremities, dry skin, blurry vision, fatigue, and sores that are slow to heal—signs that may not be a cause for concern on their own, but together can indicate a more serious problem. Patients with type 1 diabetes may also experience nausea, vomiting, and stomach pain.

While serious, the symptoms of diabetes are sometimes easy to overlook. That’s why 25 percent of people with the illness, 7.2 million in the U.S., are undiagnosed. And that number doesn’t even cover the majority of people with pre-diabetes who aren’t aware they’re on their way to becoming diabetic.

There Are 2373 Squirrels in New York's Central Park, Census Finds


Central Park in New York City is home to starlings, raccoons, and exotic zoo animals, but perhaps the most visible fauna in the area are the eastern gray squirrels. Thanks to a team of citizen scientists, we now know exactly how many of the rodents occupy the space—approximately 2373 of them, according to a census reported by Smithsonian.

In October 2018, a group called the Squirrel Census—with help from the Explorers Club, the NYU Department of Environmental Studies, Macaulay Honors College, the Central Park Conservancy, and the New York City Department of Parks & Recreation—organized a squirrel survey across all 840 acres of Central Park. For 11 days, more than 300 volunteers staked out their sections of the park twice a day—at dawn and dusk when the crepuscular animals are most active—and noted each squirrel they spotted. They also recorded how the squirrels looked, vocalized, behaved, and reacted to humans.

The research was analyzed and presented at an Explorers Club event in New York City on June 20. All the non-peer-reviewed findings—which includes a printed report, an audio report on a vinyl 45, 37 pages of data, collectible squirrel cards, and large maps of the park and the squirrel locations—are available to purchase for $75 from the Squirrel Census website.

This isn't the first time a massive census has been conducted of a public park's squirrel population. In 2011, the Squirrel Census launched with its first survey of Atlanta's Inman Park. They've conducted satellite squirrel counts at other parks, but Central Park is just the second park the organization has investigated in person.

[h/t Smithsonian]