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Don't Swallow Your Gum!
Myths, Half-Truths, and Outright Lies About Your Body and Health
By Aaron E. Carroll, Rachel C. Vreeman
St. Martin's PressCopyright © 2009 Aaron E. Carroll and Rachel C. Vreeman
All rights reserved.
Men with big feet have bigger penises
Have you ever noticed a man with particularly big feet and wondered if other parts of him were just as large? While some claim that a man's penis size can be predicted by the size of his feet, others say that it's the size of his hands or even his nose that really gives away the secret of what's in his pants. This idea of comparing body parts to estimate hidden assets may have originated with discriminating shoppers, but it may also have its roots in real science. The Hox gene in mammals plays a role in the development of the toes and fingers, as well as the penis or clitoris. Given how rarely one hears "gene expression" mentioned along with the talk of penises and feet, it seems much more likely that this myth springs from our desire, as humans, to identify patterns — even when the pattern is not really there. We like to have explanations for things we see, and we like to group like things with like things (in this case, appendages on men).
Despite the similar genetic controls for these protuberances, men with big feet do not necessarily have bigger penises. While at first, the prospects for estimating penile length with a quick glance at a man's feet seemed promising, science now shows us that this is not the case. A study of sixty men in Canada suggested that there was a weak — but statistically significant — relationship between penile length and both body height and foot length (remember — statistically significant doesn't necessarily mean significant in real life). However, a larger study of 104 men, done by two urologists, Drs. Shah and Christopher, which measured penises when pulled to their longest lengths, found that shoe size and penis size were not correlated with one another. An even larger study called the "Definitive Penis Size Survey," which looked at 3,100 men, also found no relationship between shoe size and erect penis size. This was even when men reported their size, as opposed to direct measurement. And when men are asked to report the length of their own members ... well, let's just say that science also shows us that exaggeration routinely comes into play. Furthermore, the "Definitive Penis Size Survey" was never peer-reviewed or published in a scientific journal. We trust the results from Drs. Shah and Christopher the most, but this survey backs them up. Studies also show no link between finger length and penis size. You can look at a guy's feet or hands all you want, but they won't tell you anything else about how he measures up.
You only use 10 percent of your brain
You know that you can achieve your dreams if you just put your mind to it. After all, you're only using 10 percent of your brain, right? Imagine what you could do with that other 90 percent!
It's time for a reality check. People have believed that we only use 10 percent of our brains for over one hundred years. Unfortunately, all that means is that people have been wrong for over one hundred years. As early as 1907, self-improvement gurus and motivational speakers were convincing their audiences that they could reach greater heights of achievement if only they could tap in to some of their unused, latent brain power. Some people even claim that Albert Einstein first said that most people only use 10 percent of their brains, or that he was a genius because he used more of his brain than the rest of us. Neither of these claims is true! There is no official record of Einstein saying such a thing.
The myth of the unused brain has been debunked in great detail by an expert in neuroscience, Dr. Barry Beyerstein. Many studies of patients with brain damage suggest that harm to almost any area of the brain has specific and lasting effects on a human being's capabilities. If this myth was true, it would not be a big deal to hurt various parts of your brain. Most of the time, however, that's not true at all. You will be affected by damaging almost any part of your brain.
Different types of brain imaging, including CT scans, MRI scans, and even more detailed techniques, show that no area of the brain is completely silent or inactive. Much more than 10 percent of the brain is busy at work virtually all the time. Furthermore, the many brain functions are localized to very specific areas of the brain. Each region has its own special job. When brain surgeons go in and probe the brain, area by area, they can't just find the "nonfunctioning" 90 percent, because they see functions for almost every area. Moreover, when scientists observe the responses of individual brain cells or neurons (called "micro-level localization") they do not find any gaps or inactive areas. Even studies of cell metabolism, which look at how the parts of the brain metabolize or process chemicals, reveal no dormant areas.
So, as depressing as this may be, you are probably stuck with what you've got. You are, in fact, using 100 percent of your brain. Of course, you can still question the old adage "you can't teach an old dog new tricks," since you can always keep learning new things. In fact, many studies show that keeping your brain stimulated might help to decrease dementia and brain impairment as you age.
Your hair and fingernails continue to grow after you die
Have you ever walked across a cemetery and thought about the growing, curling fingernails of the corpses beneath? This disturbing idea is probably the kind of thing you heard around a campfire as a kid. It has such a morbid appeal that artists have used this image in books and movies for a long time. Johnny Carson even joked, "For three days after death, hair and fingernails continue to grow, but phone calls taper off." Despite the popularity of this idea, it's just not true. To quote the expert opinion of forensic anthropologist William R. Maples, "It is a powerful, disturbing image, but it is pure moonshine. No such thing occurs."
This myth does have some basis in reality. After you die, your body dries out or becomes dehydrated. As the skin dries out, it shrinks (this is a different kind of shrinkage than what happens to a man in cold water). The shrinking or retracting of the skin around the hair and nails makes them look longer or more prominent compared to the shrunken skin. It's just an optical illusion, though; the nails and hair haven't actually grown at all. In order to keep growing, hair and nails require a complex mixture of hormones that are just not available to the body after death. Studies of the cellular regulation of hair growth confirm that a person would need to be alive for their hair to keep growing. There's no need to book a haircut and manicure for your corpse — no matter how long it's been since the last one.
If you shave your hair, it will grow back faster, darker, and thicker
If you are a woman with a little more hair on your upper lip than you would like, you've probably always thought that shaving that hair would make it grow back darker and thicker than before. Your mom probably warned you the first time you wanted to shave your legs that the hair would only return — but worse. And even informative health Web sites state that shaving makes the hair grow back darker and thicker. Those of you who have shaved some part of your body have witnessed how quickly that dark stubble seems to pop up.
There are great scientific studies that prove that the hair you shave off does not grow back any darker or thicker than it ever was. As early as 1928, a clinical trial demonstrated that shaving had no effect on hair growth. When the researchers in that trial shaved patches of hair on some of the people, but not on others, they did not find any difference in how fast the hair grew back. More recent studies confirm these findings.
The key to understanding this myth is knowing what really happens when hair is shaved off. Shaving removes the dead portion of hair, not the living section beneath the skin's surface. Without touching the portion of the hair that actually is responsible for growth, it is unlikely that shaving could change how fast the hair grows or what it looks like. In contrast, waxing and other forms of hair removal that pull the hairs out from below the skin actually can alter how fast the hair grows back. In fact, these methods, instead of shaving, might push the hairs into a phase of more rapid growth. So why does this myth persist?
An optical illusion is likely to blame. When you slice off the hair with a razor, it leaves a sharp end. Because these shaved hairs lack the tapered look of unshaven hair, it appears that the hair itself is thicker (even though it's not). It also may have a rougher feel because of that sharp edge. Additionally, the new hairs growing in have not yet had a chance to be lightened by the sun or other chemical exposures, so they are initially darker than existing hair — even though they will lighten up just like the other hairs over time.
And think about it: if this myth is true, we would have a way to forestall baldness in men. And, as Aaron so often tells his friends, shaving your head will absolutely not make your hair grow back thicker and faster!
You'll ruin your eyesight if you read in the dark
"Stop reading in the dark or you'll ruin your eyes!" You may remember hearing this from your parents when you were curled up in bed as a kid with your flashlight and the book that you just couldn't put down. Now, when you see other people or maybe even your own children reading away in dim light, you want to flip the light switch on or scold them in just the same way.
Dim light can certainly make you have difficulty focusing. It can also decrease how often you blink, making you uncomfortable because your eyes get dry and you squint for too long. However, the bottom line is that the effects of eye strain do not last. Once you return to good lighting, the effects go away.
There is simply no evidence proving that reading in the dark will ruin your eyesight forever. In the face of no clear scientific evidence, we have to look at what other sources we can find — expert opinions, related studies, and historical trends. The majority of ophthalmologists conclude that reading in dim light does not damage your eyes. Although reading in dim light can cause eye strain, with multiple temporary, negative effects, it is unlikely to cause a permanent change in the function or structure of the eyes.
One study did examine how the rate of blinking decreases during intense reading for patients with disorders that cause dry eyes, such as Sjogren's Syndrome. In patients with Sjogren's Syndrome, the decreased blinking and eye strain during reading can result in a temporary decrease in how well they can see. However, even in people with this condition, visual acuity improved when the patients stopped reading, again suggesting that the eyes return to their normal baseline when the strain is removed.
On the other hand, one review article on nearsightedness does conclude that "increased visual experiences," such as reading in dim light or holding books too close to the face, could result in "impaired ocular growth and refractive error" (in other words, that reading in dim light might ruin your eyes). The primary evidence cited to support this claim is that nearsightedness is becoming more and more common, and that people who read more are more likely to be nearsighted. The author notes that this hypothesis is just beginning to "gain scientific credence."
In examining this argument, we need to consider several important facts. First of all, association is not the same as causation. Just because more people who read a lot are nearsighted does not mean that the reading in dim light causes their nearsightedness. Even if they are linked, the key factor may be the amount a person reads, not the amount of light present where the reading takes place. Another important factor to consider is historical trends in lighting. Before the invention and widespread use of lightbulbs, people had to rely on reading by candlelight in dark rooms. Now, most of us have access to light for reading whenever necessary. We have never had better light for reading in the history of the world. In that sense, the fact that more people are nearsighted today, when the world is so well lit, does not support the idea that reading in dim light hurts your eyes.
Thus, our conclusion is that definitive scientific data do not exist to support or refute the claim that reading in dim light will ruin your eyesight, but the majority of experts believe (and common sense suggests) this is not true.
The average person swallows eight spiders per year
Rachel hates spiders. This situation was not improved when an East African jumping spider bit her last year. Even though Rachel knows all of the logical reasons why she should like spiders, they really creep her out. And Aaron had a horrible experience with a brown recluse spider bite on the middle of his forehead (which made his brother call him "the unicorn"). The thought that we are routinely swallowing spiders in our sleep is incredibly freaky to both of us. You can imagine that someone may have first told someone else that they were swallowing spiders because they wanted to scare people just like Rachel, and the thought was so creepy that it stuck around. A 1954 book about insect folklore contained this myth, and most versions of this myth that are passed around imply that you are swallowing these spiders while you sleep. In 1993, Lisa Holst wrote a magazine article describing how this swallowing spiders idea was a myth, "a ridiculous belief of the sort that someone would actually believe." And, in classic myth-spinning form, now people quote her article as a source documenting that people actually do swallow spiders every year (even though that is the exact opposite of what she was saying).
How do we know that the average person is not swallowing eight spiders per year? Can we prove that this does not happen? No. There are no great studies to prove that this does not happen, but there are also no studies to prove that this does happen. We could not find any studies documenting any instances of people accidentally swallowing live spiders. And without any science or evidence, there is no reason to believe that this is actually happening. Furthermore, there are a lot of reasons why it is virtually impossible that people are swallowing so many spiders.
We'll be the first to admit that we are people doctors, and not experts on spiders. Therefore, we must turn to spider experts, such as the frighteningly dedicated aficionados at www.spiderzrule.com. (This site must be seen to be believed.) Why don't we routinely swallow spiders in our sleep? First of all, most people roll around in their sleep. This rolling around would probably scare the spiders from wandering anywhere close to your face. Second, you would need to have your mouth open, and not everyone keeps theirs open while they sleep. Third, insect experts tell us that spiders, like other arthropods, instinctively flee from open, breathing mouths. This makes sense — if you are an arthropod, unless you are suicidal, you are programmed to try to avoid things that might eat you. Finally, the spider would have to walk into your mouth and stay there in such a way that your swallowing reflex was triggered. We do not automatically swallow every time something goes into our mouths. The chance that all of these things would happen together — that there would be a wandering, potentially suicidal spider in close vicinity to your mouth and that they would actually wander in to the wet, dark, breathing space and trigger your swallowing reflex — is really incredibly small.
Still, some will claim that a spider could fall into your mouth. What if it was hanging from the ceiling just above your mouth? The odds of this happening are also incredibly small. Your mouth is a relatively small target for a spider to hit randomly. And before you start worrying that eight spiders are going into your stomach every year through your nose, it's even more unlikely that you would swallow them this way than if they actively chose to crawl into your mouth. Your nostrils are (we hope) even smaller than your mouth, and thus an even smaller target for the spiders to hit. The most likely scenario if a spider actually went into your nose is that you would sneeze it out. The sneeze reflex is very sensitive, and recognizes when even a small piece of dust gets in the nose.
So, it is possible that you have swallowed a spider, perhaps even more than one. But it is incredibly unlikely that you have swallowed eight in the last year. Or that enough people are swallowing spiders that each person would average eight (or any significant number) in a year. It's a myth all around.
Excerpted from Don't Swallow Your Gum! by Aaron E. Carroll, Rachel C. Vreeman. Copyright © 2009 Aaron E. Carroll and Rachel C. Vreeman. Excerpted by permission of St. Martin's Press.
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