Everything You Know About the Human Body is Wrong E-Book

Matt Brown

• Herausgeber: Batsford
• Kategorie: Wissenschaft und neue Technologien
• Sprache: Englisch
• Veröffentlichungsjahr: 2023

Seitenzahl: 183

Beschreibung

A highly entertaining book debunking the many myths about the human body. Everything You Know About the Human Body is Wrong debunks the scientific myths we all take for granted. Written by author Matt Brown in his trademark humourous style, this book takes you through all the facts we thought true, from bodily blunders, medical mis-quotes and curious cures. Does giving kids sugar make them go hyper-active? Not at all – there is no proven link! Is there such a thing as being 'double-jointed'? And is it dangerous to swim after eating? Covering everything from pseudoscience to recent research, Everything You Know About the Human Body is Wrong shatters a range of illusions we have accepted unquestioningly since childhood and demystifies this most puzzling of subjects.  

Leseprobe

EverythingYou KnowAbout theHuman BodyIs Wrong

EverythingYou KnowAbout theHuman BodyIs Wrong

Matt Brown

Contents

Introduction

Body basics

We know everything about the human body

Humans have five senses

Humans have ten fingers

Most body heat is lost through the head

Veins are blue and arteries red

Humans need a solid eight hours of sleep every night

Women have more ribs than men

Same thing, different name

Organs

Your stomach is down behind your belly button

The liver is the largest organ

Humans only use 10 per cent of their brains

You’re either a left-brain person or a right-brain person

A flatlining heart can be restarted with a defibrillator

The appendix has no known function

A miscellanea of dodgy folk tales

The microscopic body

All the cells in your body contain 46 chromosomes

All the DNA in your body is found in your chromosomes

Most humans contain very little metal

Skin cells are the main component of household dust

Sex myths

The hungry body

Sugar makes children hyperactive

Alcohol kills brain cells

Eating before swimming causes cramps

Pregnant women are eating for two

Your tongue detects four types of taste

Five food myths that don’t pass muster

Body oddities

Future humans will have tiny fingers through texting a lot

Identical twins are truly identical

Humans can spontaneously combust

Fingernails and hair continue to grow after death

Shaving causes hairs to grow back faster, or rougher

Some people just don’t fart

Dead bodies are inert

An A-Z of quackery

The body compromised

You’ll catch a cold if you go out in the rain

Vitamin C prevents colds

Tapeworms can help you lose weight

Smallpox has been entirely eradicated

‘Ring a Ring o’ Roses’ is all about the Black Death

Watching lots of TV is bad for your eyes

Vaccines can cause autism

Famous bodies

Richard III had a disfiguring hunchback and walked with a limp

Anne Boleyn had 11 fingers

Napoleon was very short

Jeanne Calment was undisputedly the oldest person who ever lived

The golden Bond girl shows how paint can asphyxiate

And a few more odd bods …

Are you pronouncing it wrong?

Other myths, misconceptions and misnomers

Let’s make up a new wave of false facts

Index

Other titles in the series

About the author

Introduction

We spend every moment of life inhabiting our bodies. Nothing in the world is more familiar. Yet the human body is also very unfamiliar. Unusual circumstances aside, few of us ever see or touch the vast majority of our own bodies. It is a rare and unlucky person who gets to view his own femur or examine her own spleen.

The ancient Greeks had a saying: ‘Know thyself’. Few of us come close. The inside of the body is a complicated, three-dimensional morass of organs, vessels, valves, tendons, muscles, fluids, bones, nerves, cartilage, nodes, sacs, flaps and countless other tissues beyond cognizance. You might spend years mastering the gross anatomy, and still have much to learn.

The human body is home to hundreds of species of bacteria, with many fungi, viruses and even animals along for the ride. Can anyone ever know the body at a cellular level? Scientists are only beginning to piece together the molecular machinery that underpins the whole enterprise. It would be a lesser task to memorize the whole of human literature than to carry out a complete survey of every physiological process in one human being.

Our bodies are marvellous, in the true meaning of that word. Nothing ever discovered or created comes close to the human brain in complexity or ability. The brain remains the most mysterious component of the body. We might be close to understanding how memories form, for example, but we are nowhere near appreciating how the physical memory encoded in neurons turns into a re-lived experience somewhere in our heads.

As such an intricate, complicated and still partly mysterious entity, the human body is a fertile breeding ground for myths and misunderstandings. Unless you study it for a living, you’ve probably got very little idea how your gut works, how pain is transmitted from your fingers to the brain, or how a fetus develops in the womb. But because our bodies are the ultimate personal possessions, we all like to have working theories. Many old wives’ tales still linger from simpler times, when nobody really knew what caused colds, cold sores and cancers.

This book is part of an ongoing series that examines and debunks the common myths of our daily lives. As with other volumes, the aim is not to ridicule or belittle, but to open the eyes to the infinite joy of knowledge. We learn most powerfully from our mistakes. A book exposing those mistakes should be more memorable than a straightforward tour of the body. And more fun.

Many of the entries in this book touch on issues of health and wellbeing. While I have, of course, striven for accuracy, any information herein should not be treated as a substitute for the medical advice of a doctor or health-care professional. Further, the reader is encouraged never to take statements at face value, including ones made here. Always dig if something sounds dodgy.

Let the nitpicking commence!

A NOTE ON SOURCES: Wherever relevant, I’ve checked my facts by consulting the scientific literature – research articles that have been carefully reviewed and published in respected journals. A book like this needs to strike a balance. To cross-reference every other sentence would be cumbersome and tedious, but to leave out all references would be negligent. I’ve therefore included references for information that is either particularly surprising, or for which the reader might enjoy probing a bit deeper than my own word limit allows. In such cases, I’ve cited the name of the first author and a ‘doi’ number. The doi, when typed into an Internet search bar, should lead you to an online version of the article (although it may be partially behind a paywall).

We know everythingabout the human body

Imagine climbing on board an aeroplane that nobody understands. The pilot is sure which buttons to press and which sticks to pull, but she has no clue why the plane stays in the air. The ground crew are able to make repairs and know that they must fill the plane with kerosene, but they don’t understand how this makes the plane move, let alone fly. Even the aircraft’s designers don’t get it – they rivet some wings and a tail onto a fuselage and it somehow takes off. It works every time, so everyone carries on flying.

This scenario is clearly ludicrous, but it’s not far from the situation with anaesthetics.

For most of history, patients undergoing surgery had to endure unimaginable horror. Flesh was cut and bone was cleaved without any effective pain relief. Then, from the mid-19th century, anaesthetic gases became available. This changed everything. After a few decades of trial and error, the use of anaesthetics removed most of the terror from the surgeon’s table. Speed was no longer of the essence, and patients had no capacity to writhe around. Those wielding the scalpel could do so under controlled conditions and survival rates rocketed accordingly. Modern anaesthetics are extremely safe (when administered by a professional), reliable and used millions of times each year.

Nobody knows how they work.

Clearly, a general anaesthetic must act on the brain in some way. The agent turns off consciousness, while leaving other brain activities intact. There are theories on how the chemicals in the anaesthetic interact with the brain, but nobody has yet set out a detailed mechanism. It goes to show just how much we still have to learn about the body that, after a century-and-a-half of use, anaesthetics retain this mystery.

The human body, it hardly needs saying, is complex. Modern imaging techniques have taken knowledge to levels unimaginable only a few generations ago. And yet there is still much to learn – not just at the level of molecules and biochemistry, but even in the realm of anatomy, which concerns itself with the body at larger scales.

In early 2017 newspapers around the world announced that the body has a new organ. For decades, doctors had counted 78 organs, but a new discovery had topped that up to 79*. How, after thousands of years of study, could we have missed a whole organ? The culprit is a part of the digestive system known as the mesentery. It connects the intestine to the stomach. This is a pretty important junction. Indeed, the mesentery has been known since antiquity, so in one sense it’s a little disingenuous to repeat the newspaper headlines of 2017 and describe it as a newly discovered organ.

In another sense, it really is a startling find. Doctors had always assumed that the mesentery was made up of a few fragmentary pieces, but more recent scrutiny shows it to be a single structure. Hence, it now looks set to join the other organs on an equal footing.

What other mysteries lie within? Enough to keep the Nobel Prize for Physiology and Medicine well stocked with winners for the foreseeable centuries. The brain remains the most obvious conundrum. Knowledge of that organ leaps forward every year, but nobody knows how memories, thoughts and emotions can arise, and be experienced, within its bounds. How can a few pounds of intelligent tofu, evolved over millennia to catch gazelle and forage for berries, also calculate the composition and gravity wells of distant stars – and be self-aware enough to contemplate this impressive ability?

Why are the vast majority of humans right-handed, independent of culture and background? Indeed, why do we have one dominant hand anyway? Why did humans evolve different blood types, or unique fingerprints, or the ability to blush (which can put us at a social disadvantage)? Do pheromones play a role in human sexual attraction? Why have we kept some clumps of body hair and not others? Why does childhood and adolescence last so long in humans compared with other primates? The list is as long as your arm. Indeed, why your arm should be much weaker than a chimp’s when you have similar musculature is just another example.

*FOOTNOTE: This tally was widely reported in the newspapers, probably inspired by Wikipedia. It is spurious. There is no officially agreed number of organs in the body. It depends on how you define an organ. A common description holds that an organ is a self-contained part of the body that performs a specific function or functions. The heart, say, is a stand-alone unit with the clear task of pumping blood around the body. But the definition is a bit wishy-washy. My big toe is also a discrete, self-contained part of my body with the sole function of keeping me on my feet – why does that not count as an organ? How about all the bones in the body? The tally of 78 or 79 organs makes for good copy in newspaper stories but is not supported by the anatomical community.

Humans have five senses

You might have seen or heard that humans have five senses, but if you sniff around, you’ll get the feeling that this is just a taster. As well as sight, hearing, smell, touch and taste, our bodies have a whole motherboard of sensors that give us information about our environment.

Close your eyes and lean forward. Even without seeing, you know that your body is close to tipping over. The information is not wholly coming from your sense of touch. We all carry something analogous to a spirit level in our heads. The inner ear contains three loop-shaped canals filled with fluids. As the head tilts or rotates, the fluids shift position. This movement is registered by tiny hairs, which in turn send signals to the brain. The brain determines if corrective motion is needed and instructs the muscles accordingly. We call it our sense of balance, and it is mediated by the vestibular system. There’s no reason not to count it as a sense.

Then we have proprioception. This is the ‘where?’ sense that reports back on the body’s conformation – simplistically, the direction in which your arms and legs are pointing or moving. With eyes closed, most people can touch their nose or scratch their head. Walking in the dark is physically no harder than walking in the light, so long as you know the path is clear. Proprioception has its own sensors called – logically enough – proprioceptors. These are special sensory fibres within the muscles that give feedback to the brain.

We can add still further powers to the sensorium. Our sense of touch, for example, can be broken down into its different facets. Pain, pressure, itches, heat and cold all feel different on the skin. This is because each is registered by a different type of receptor, and we might therefore regard them as separate senses.

Arguments can be made for still further senses. If we consider proprioception to be a sense, then why not other internal signals such as hunger or thirst? Ultimately, it’s down to how one defines a sense, but it’s clear that the traditional five are only part of the story.

We may have more than five senses, but our sampling of reality is hopelessly limited. Take our sense of sight. Only a fraction of the light that enters our eyes will trigger photoreceptors. Here, ‘fraction’ is an understatement. The visible spectrum is less than one-thousandth of 1 per cent of the wavelengths that hit our eyes. We never evolved the ability to see microwaves, UV, infrared, or any other flavour of electromagnetism beyond the spectrum of colours*.

Perhaps one day humans will enhance our senses through genetic engineering or technological bolt-ons. Might we soon be able to ‘see’ radio waves, or watch as microwaves cook our food, or enjoy 360-degree vision? Maybe our perception will grow to encapsulate the experiences of other humans, or even machines.

Experiments have already been conducted into sensing group emotions. Algorithms assess and compile the thoughts of thousands of people, as expressed on social media. The output is sent to a tactile vest, which bulges and buzzes to convey the emotions. The wearer learns to interpret prods from the vest and thereby ‘feel’ the sentiments passing around online. Even the colloquial ‘sixth sense’ of mind reading could become a possibility through technology. Crude, mind-controlled artificial limbs are already a reality. As we learn more about the brain, it may become possible to hook up transceivers that send messages directly between minds. Then again, people have been saying that for generations.

Some animals already do have additional senses not open to humans. They experience a different reality we can only begin to imagine. Migratory birds, and even the humble robin, are able to ‘see’ the Earth’s magnetic field. It helps them to navigate. Some snakes can see infrared. Other animals – such as sharks, platypuses and bees – can detect electric fields. Sharks use this talent to sense the tiny electric signals in the muscles of prey. Certain species of dolphin can do this too. Add on the echolocation used to find their way through murky water, and dolphins might just be the most sensitive mammals of all.

*FOOTNOTE: Or, rather, what we perceive as colours. There is nothing intrinsically yellow about a banana, and the sky is not in itself blue. Objects reflect and refract light in different ways, which we observe as different colours – but only because the human brain has evolved to file things that way. Some animals don’t experience any colour, others can perceive light at wavelengths beyond our abilities. The banana would look very different in either case. We can imagine a creature that perceives different wavelengths of light as clicks of different frequency, rather than a visual sensation. The quality of ‘yellowness’ is merely an interpretation of an input. It’s all in the brain, not in the banana.

Humans have ten fingers

You can tell if your child is going to be a pedant. The warning signs start early: when ‘Can you count to ten on your fingers?’ is answered by, ‘No, but I can count to eight, because I only have eight fingers, and two thumbs,’ then you know you’ve got a nitpicker in the family.

If you’re the kind of person who likes to get competitive with small children, then you might counter the eight-finger assertion by showing the child a dictionary. Most allow both definitions. Depending on context, it’s legitimate to say either that humans have eight fingers or ten fingers.

A pedantic uncle, listening in, could go still further. ‘A given person might have ten (or eight) fingers,’ he might say, ‘but humans, on average, do not.’ He would argue that many people lose fingers or hands during life, whereas very few are born with additional digits. Across the world population, this lowers the average number of fingers to something like 9.9. ‘If you have ten fingers,’ he’d conclude, ‘then you have an above-average number of digits.’

‘Aha!’ cries a nitpicking aunt, who has been following with interest, ‘But that only applies to the mean. Other measures of the average, such as median and mode, would still give an answer of ten fingers.’

It is at this point that you back away from the conversation, wondering what you’ve started. You vow never to get your fingers – whether eight, 9.9 or ten of them – burned again.

Most body heat is lostthrough the head

I must confess, as a gradually balding man, I’ve paid particular heed to this pearl of wisdom. Rarely will I venture outside on a cold day without my woolly headgear. So, I was most surprised to learn when researching this book, that there is no evidence to suggest the body loses most heat through the head. It’s not even a particularly recent myth, but hats off to its tenacity.

Like all good fiction, the notion is underpinned with a convincing back story. The brain, it is said, uses so much energy that it radiates far more heat than any comparable area in the rest of the body. Hence, you should wear a hat in cold weather, or risk hypothermia.

This received wisdom was debunked in no lesser publication than the British Medical Journal – one of the world’s leading scholarly journals*. The authors say that any uncovered part of the body would lose heat about as rapidly as any other. The head has no special radiative properties. It is simply the part of the body most often left uncovered. Few would go out in freezing conditions without a coat, but they might eschew a hat.

The myth has been traced back to an influential US Army survival manual of the 1970s, widely read by the general public, as well as service personnel. The guide suggests that up to 50 per cent of body heat is lost through the head – a claim repeated in modern versions of the manual. The assertion is thought to be based on flawed military research from the 1950s. Subjects were wrapped in survival suits and placed in Arctic conditions. They did indeed lose most body heat through their heads, but only because they weren’t wearing hats. Had they been exposed in just their underwear, they would have lost heat proportionately from every nude surface.

The original military research is never properly cited and I’ve found it impossible to track down. It may itself be a myth, or a garbled truth. Even so, better documented research has arrived at the same conclusions. In one study (T. Pretorius et al., 2006, doi:10.1152/japplphysiol.01241.2005), researchers dunked hardy volunteers into cold water. Some were lowered up to their chins, others were completely submerged (wearing scuba gear). The experimenters could then measure the changes in body temperature. The head ‘does not contribute relatively more than the rest of the body to surface heat loss,’ they found.

In other words, if you were to stroll naked through the Arctic tundra, you would lose heat equally from all parts of your body. Perhaps 10 per cent of that loss would come from the head. But there is a catch, and one which throws a lifeline to the old myth. If you do wrap up warm but leave your head exposed, then your core temperature could suffer. The scalp contains more blood vessels than most other surface areas. Exposure cools the blood flowing through, which then travels down to the core. There’s still every reason to wear that woolly hat in cold weather.

*FOOTNOTE: That said, it is reported in a whimsical Christmas-themed article, rather than a peer-reviewed write-up. Some scepticism is required.

Veins are blue andarteries red

Some people think that human blood is blue. I had no idea that such a misconception existed until I started researching this book, but it seems to be a fairly common belief. The pseudoscientific reasoning goes like this. Anyone with light skin can see that veins are blue, just by looking at the back of their hand. The veins are blue because they contain blood that is blue. The blood only turns red when it is oxygenated by the lungs and pumped away through the arteries. We don’t see blue blood when we cut ourselves, because it immediately oxidizes on contact with air, and turns red.

It sounds mildly convincing but just about every sentence in that chain of statements is flawed or wrong. Nobody has blue blood, not even the Queen. Blood does come in different shades of red – a bright crimson when oxygenated in the arteries, and a duller, darker colour when venous – but never, ever blue. Where does the idea come from?