100 Mysteries of Science Explained

by Popular Science

  Tickling while horsing around also may have given rise to laughter itself. “The ‘ha ha’ of human laughter almost certainly evolved from the ‘pant pant’ of rough-and-tumble human play,” says Provine, who bases that conclusion on observations of panting in apes that tickle each other, such as chimpanzees and orangutans. In adulthood, our response to tickling trails off around the age of 40. At that point, the fun stops; for reasons unknown, tickling seems to be mainly for the young.

  Why Do We Yawn?

  We all do it, and even some animals as well, when we’re ready to go to sleep and sometimes when we awake. We do it when we’re bored, and we might do it under stress. We can even catch it from another person, but as common as yawning is, scientists have struggled to explain why we yawn. Recent research suggests some possible explanations.

  One theory among chasmologists—scientists who study yawning—is that the act is a form of social behavior. Contagious yawns are quite common—about half the people who see or hear a yawn will yawn too. Christian Hess of the University of Bern in Switzerland thinks the easy spread of yawns helped early humans learn to synchronize their desire to go to sleep and awake at the same time, allowing them to coordinate their daily activities.

  Maryland psychologist Robert Provine is one chasmologist who thinks a yawn stirs up our brains. So when we’re sleepy, a yawn wakes us up, and if we need mental sharpness to deal with stress, the yawn provides it. As part of this theory, the yawn could be stimulating the flow of cerebrospinal fluid, which clears out chemicals in the brain that make us sleepy. The brain-stimulating yawn also has a social component: Provine says a contagious yawn spawned by stress could signal members of a group to prepare for danger.

  Instead of synchronizing bedtimes or sweeping out unwanted chemicals, a yawn could regulate temperature. That’s the theory of Andrew Gallup, a psychologist at the State University of New York at Oneonta. Basically, he says, “We yawn to cool our brains.” Yawning increases the flow of blood to the brain, forcing out warm blood that has gathered there. Simultaneously, the yawn brings cooling air into the body through the mouth and nose. A typical yawn, Gallup said, can lower the temperature in the brain by 0.2 degrees Fahrenheit. A string of yawns can lower it by half a degree more.

  Working off this theory, Gallup and some scientists in Vienna tested the incidence of contagious yawning at different temperatures. Their results suggested that contagious yawning most often takes place when the outside temperature is in a “thermal window” of around 68 degrees Fahrenheit (20 degrees Celsius). Yawning decreases when the outside temperature and body temperature are close, or when it’s cold outside.

  The number of school-age children with peanut allergies has doubled in the past decade. Yet scientists have not identified what makes the legume such a threat or why the allergy has become so prevalent.

  Why Are Peanut Allergies on the Rise?

  Typically, the immune system treats peanuts as safe, but some scientists believe that early and heavy exposure to peanut-laden products might cause the immune system to misidentify them as dangerous. This theory is strengthened by the fact that 8 out of 10 allergic kids have a reaction the first time they eat a peanut, indicating a previous indirect exposure, possibly even in the womb or through breast milk.

  Theories about peanut allergies abound and most involve an overactive immune system. “We have done such a good job of eliminating the threats that the immune system is supposed to manage that it’s looking for something to do,” says Anne Muñoz-Furlong, former CEO of the nonprofit Food Allergy and Anaphylaxis Network. Parents today feed their kids a lot of ready-made snacks, many of which contain peanuts or their derivatives. “We’re bombarding the immune system with these [food-based] allergens, so it’s attacking those instead.” Indeed, food allergies in general are on the rise.

  But peanuts seem to trigger especially violent immune reactions. This might be because they contain several proteins not found in most other foods, posits Robert Wood, an allergy specialist at Johns Hopkins University, and the structure of these proteins can stimulate a strong immune response. Research suggests that roasting peanuts, as American companies do, might alter the proteins’ shape, making them an even bigger target. Allergy rates are lower in China, where it’s customary to boil peanuts, which damages the proteins less. (It’s worth noting, though, that China is also more polluted, so people’s immune systems might be concentrating on traditional threats.)

  Or maybe it’s all the time indoors. Children who spend little time outdoors tend to be deficient in D, Wood says, so their bodies might mislabel peanut proteins as dangerous. Parents looking to protect their kids might consider sending them outside—and not washing their hands when they come home.

  Do you ever wonder why you forgot what you were looking for as soon as you set off to find something? Or why you can’t recall the ending of a book you read last year?

  What Is a Memory?

  Scientists say there could be a reason why you don’t remember what you ate for breakfast last week but can vividly describe your first day of kindergarten. Emotional meaning attached to a memory makes it stick in a way that everyday details can’t. But memories aren’t just about the past. They help us learn and make decisions about the future.

  Neuroscientists do not completely understand the physical representation of memories in the brain. Neurons, or brain cells, communicate with each other through electrochemical pathways. An electrical impulse travels down the outgoing branch called an axon, where it stimulates fingers known as dendrites at the end, releasing neurotransmitters. These tiny molecules send messages that incoming branches pick up. The space between these branches is called a synapse.

  The reconstruction of a past experience happens through synchronous firing of neurons involved in the original experience. A memory is not a static entity but a unique pattern of activity that can shift or migrate between different parts of the brain. It is like a jigsaw puzzle that assembles throughout various areas of the brain, rather than a video clip stored as a whole file. Short-term memories do not “stick” in the synapse, and long-term memories might be distorted when they reassemble.

  One of the most important attributes of memory is our ability to learn. When we learn or recall information, we use memory to retrieve the idea we have learned. Every time you eat, drive a car or read a book, you are remembering learned traits. New technology called optogenetics uses light beams to excite or silence a targeted group of neurons in the brain, helping scientists study and perhaps control memories. It may be possible to open up a pathway to selectively implant memories or erase certain memories altogether. For people with amnesia or severe emotional trauma, that will be a moment worth remembering.

  Why Do We Dream?

  Dreams remain one of the most mysterious aspects of the human experience. Diviners, doctors and scientists have pondered the phenomenon of dreaming for centuries. Despite a plethora of competing theories that attempt to explain why we dream, no particular idea has achieved a consensus among researchers.

  The classic exploration of dreams—the one that pop culture invokes time and time again—is Freud’s, The Interpretion of Dreams published in 1899. The founding psychotherapist believed that dreams are our mechanism for living out our most aggressive, carnal desires—the urges that we’re not allowed to act on in real life—so that we don’t go insane from repressing them during the daytime. Though the field of psychoanalysis has largely moved on from Freud, our need to ascribe meaning to our dreams and to master our subconscious renders the Freudian approach compelling to this day.

  On the other hand, minimalist sleep researchers propose that dreams are devoid of any objective meaning. Harvard psychiatrists J. Allan Hobson and Robert McCarley generated a firestorm of controversy in 1977 when they argued that dreams are nothing but the side effects of spontaneous activity taking place in the synapses in the brain stem during sleep. In other words, our dreams (and the meanings that we ascribe to them) are nothing but our s
ubjective attempt to reconcile those mental stimuli.

  In between these two extremes are a slew of theories that frame dreams as functionally, if not necessarily psychologically, important. Experiments show that dreams help subjects solve problems and puzzles that researchers posed to them before dream sleep. This finding jibes with theories that dreaming is crucial to memory storage, information processing, and cleaning out the synaptic garbage that the brain collects as a result of its normal operation. Other research indicates that dreams play an important role in stress relief, a theory supported by a decrease in stress hormones during dream sleep.

  Psychologist Deirdre Barrett, also of Harvard, focuses on our least favorite subset of dreams: nightmares. She claims that even these unwelcome dreams once posed the important evolutionary function of focusing attention on the dangers our ancestors faced in everyday life. All these functionalist hypotheses suggest that dreams developed as a function of the mammalian brain in order to fulfill an evolutionary purpose. What that purpose is remains a puzzle. Perhaps we should sleep on it?

  Why Do We Laugh?

  We hear laughter all the time—from a giggle to a snicker to a full-blown belly laugh. Laughter is undoubtedly a common human behavior, yet it has vexed scientists for centuries. To this day, the question “Why do we laugh?” remains a much-debated topic.

  An apparent answer to the question would be that we laugh when we think something is funny. In this case, laughter—the contractions of facial muscles accompanied by an audible sound ranging from a quiet titter to a loud cackle—would be the physiological response to humor. This might be the answer, but it’s not the full story. The reasons that we need this response are more complicated than you’d think.

  As it turns out, studying laughter is no joking matter, according to Robert R. Provine, professor of psychology and neuroscience at the University of Maryland. Provine, the author of the book, has conducted numerous studies on mirth. “Most laughter is not in response to jokes or humor,” says Provine. Most of it occurs in ordinary conversations, in which nothing at all humorous transpires. In one of his most-publicized studies, Provine observes that laughs can be elicited by a variety of non-joke statements such as “Hey, John, where ya been?” or “How did you do on the test?”

  “It is about relationships between people,” claims Provine. “We don’t decide to laugh at these moments. Our brain makes the decision for us. These curious ‘ha ha ha’s’ are bits of the social glue that bond relationships.”

  Provine believes that human laughter predated human speech by millions of years. Before speech, laughter was a primary form of communication. “Laughter,” says Provine, “evolved from the panting behavior of our ancient primate ancestors.” Apes and other animals, including rats, make “laugh-like” sounds and high-pitched vocalizations while playing, but it would be erroneous to equate them with human laughter. However, “When we laugh, we’re often communicating playful intent. So laughter has a bonding function between individuals in a group,” says Provine.

  While most laughter is a positive behavior, it can have negative intent. Pointing out one social function of laughter, Provine cites the difference between “laughing with” and “laughing at” someone. “People who laugh at others may be trying to force them to conform or casting them out of the group,” he says.

  While studies have yet to prove that laughter is the best medicine or has any appreciable degree of health benefits, for that matter, Provine notes, “If we enjoy laughing, isn’t that reason enough to laugh? Do you really need a prescription?”

  Spherical-shaped Staphylococcus bacteria (shown in purple and yellow) try to escape destruction by white blood cells in these colorized scans. Scientists think that this kind of cell activity might create noise—but they don’t yet have proof.

  Do Cells Make Noise?

  You have to listen very, very closely, but yes, cells produce a symphony of sounds. Although they won’t win a Grammy anytime soon, the various audio blips produced by cells give scientists insight into cellular biomechanics and could even be used to help detect cancer.

  Researchers at the University of California at Los Angeles studying brewer’s yeast discovered that the yeast’s cell walls vibrate 1,000 times per second. These motions are too slight and fast to be caught on video, but when converted into sound, they create what the scientists describe as a high-pitched scream. It’s about the same frequency as two octaves above middle C on a piano, but it’s not loud enough to hear with the naked ear. “I think if you listened to it for too long, you would go mad,” says biological physicist Andrew Pelling, at the University of Ottawa. Pelling and Jim Gimzewski, a professor of biochemistry at UCLA, theorize that molecular motors that transport proteins around the yeast cell cause the walls to vibrate.

  It’s a little harder to get sound out of a human cell than from a yeast cell: So far, scientists have not observed mammalian cells that audibly shimmy on their own, at least in part because animal cells’ wiggly membranes are less likely to vibrate than the sturdy cell walls of yeast and plants. But human cells certainly squeal when zapped with light, a trait that could be surprisingly useful for medical science, particularly cancer research.

  When Richard Snook and Peter Gardner, biologists at the University of Manchester in England, blasted human prostate cells with infrared light, their microphones picked up thousands of simultaneous notes generated by the cells. Through statistical analysis of these sounds—which are created as the cells rapidly heat up and cool down, causing vibrations in the air molecules directly above them—Snook and Gardner can differentiate between normal and cancerous cells. “The difference between a healthy cell and a cancer cell is like listening to two very large orchestras playing their instruments all at the same time,” Gardner says. “But in the cancerous orchestra, the tuba is horribly out of tune.” Gardner is fine-tuning the technique in hopes of replacing current, unreliable pre-biopsy prostate-cancer tests. His ultimate goal is to reduce the number of prostate biopsies performed, 75 percent of which come back negative.

  Your brain—the 3-pound (1.3-kg) blob of neurons, chemicals, hormones, water, and fat sitting in your skull—is the most complex part of the human body.

  How Does the Brain Work?

  The main functional unit of the brain is a type of nerve cell called the neuron, of which the human brain possesses roughly 100 billion. The human body contains three types of neurons, each different in function. Sensory neurons carry signals from the outside world into the central nervous system. Motor neurons carry signals from the central nervous system to muscles and glands. Interneurons form a connection between other neurons; they are neither sensory nor motor. Each sensation, memory, thought, and movement we experience is the result of electrochemical signals that pass through neurons. The ability of our brain to function is the result of the 24/7 activity of neurons.

  The human brain consists of the brain stem, the cerebellum, the cerebrum, and the limbic system.

  The BRAIN STEM contains the medulla, which regulates heart rate and breathing; the pons, which links to the cerebellum to help with movement and posture, as well as creating a certain level of consciousness necessary for sleep; and the midbrain, which helps regulate body movement, hearing, and vision.

  The CEREBELLUM, often called “the little brain,” allows the body to move properly, controlling functions such as posture, balance, and coordination.

  The CEREBRUM is the largest part of the brain, and responsible for most of its functions. It is divided into four sections: (1) the frontal lobe, which controls, among other things, intellect, judgment, creative thought, problem solving, muscle movements, smell, and personality; (2) the parietal lobe, which focuses on comprehension and monitors visual functions, reading, and tactile sensation; (3) the temporal lobe, which controls visual and auditory memories; and (4) the occipital lobe, which is responsible for processing visual information. The cerebrum is split into a left and a right hemisphere, connected by neurons that pass inform
ation from one side to the other.

  The LIMBIC SYSTEM contains glands that help relay hormonal responses in the body. The amygdala is responsible for the response and memory of emotions, especially fear. The hippocampus helps process long-term memory and emotional responses. The hypothalamus controls hunger, thirst, and body temperature, while the thalamus helps control attention span and monitors information in and out of the brain to track bodily sensations, such as pain.

  The regions of the brain frequently work independently, but sometimes different regions work together to perform a task. For example, several regions in the brain function cooperatively to allow us to read. MRI brain scans show that the ability to sound out printed words is a function of a part of the parietal lobe, while making connections with a new word and sound is associated with the cerebellum and hippocampus. The ability to read out loud quickly appears to be a function of several brain locations.

  Despites centuries of scientific study, however, we are at still at a loss to explain many of the human brain’s mysteries. Among the unsolved puzzles scientists are trying to unravel are the following:

  How are memories stored and retrieved?

  How do brains make sound predictions about the world?

  What does “intelligence” mean in biological terms?

  Getting a stronger grip on the functioning of the brain could have enormous ramifications. According to Norman Weinberger, a neuroscientist at the University of California, Irvine, “If we understand the brain, we will understand both its capacities and its limits for thought, emotions, reasoning, love, and every other aspect of human life.”