The majority of you is made up of six elements, and 99.9% of your DNA is exactly the same as everyone else’s—yet, both the human body and you are unprecedented mysteries. We’re the only organisms to cry out of sadness, and our brain shows us the future a fifth of a second before it actually happens. Enigmas like these riddle human anatomy and continue to baffle microbiologists, neuroscientists, and psychiatrists alike. Bestselling author Bill Bryson details the vivid story of the human body, drawing upon eye-opening facts—like the one that says our eyes don’t really see a majority of what we think they do—and scientific research to lead us further into the discovery of ourselves and the world of us.

Have you ever experienced that annoying itch that just won’t go away no matter how hard you scratch? So did a woman referred to as M., who in getting rid of that irritating skin sensation, actually scratched straight through to her brain. She didn’t even realize she was doing it, either; most of her itching took place while she was asleep. Don’t worry, though—this is a medical anomaly. Still, it speaks to the greater mystery of the human body since scientists not only have no clue why M. simply couldn’t satisfy her itch, but they also have no idea why we even develop  an itch in the first place.

Despite the inevitable mystery surrounding our human anatomy, there’s plenty scientists do know about skin. For instance, skin is our largest organ, and it’s a part of something called the cutaneous system which houses both our dermis and our epidermis. Rather morbidly, the author notes, our epidermis, or the outer portion of our skin, is made up of entirely dead cells. The inner layer of your skin is the dermis, and it contains receptors that allow you to experience the world. Some of these receptors are called Meissner’s corpuscles, the kinds of sensors that allow you to pick up on the most delicate touch, like on your fingertips or your lips. How you perceive the world through your senses is due largely in part to these sensors, but the brain also plays an integral role. The author notes that your brain actually tells you how a touch should feel depending on who or what it’s coming from and the setting you are in.

The science of skin also proves that race doesn’t really exist. According to paleobiologist Nina Jablonski at State College in Pennsylvania, what we see as race is accounted for by a single tiny molecule that adds color to our skin and to the features of various animals. This molecule is called melanin, and it’s the source of differing skin tones, the only known biological difference in people of different racial backgrounds. Due to a process called phenotypic plasticity, skin tones evolved in the past according to the particular environment the person lived in, and continue to change now in response to sun exposure. The author observes that melanin is what gives us dark freckles after a long day in the sun, as our body works to protect us from the harmful rays.

Our skin is a powerful mechanism that does more than simply keep our organs in place. While there’s still much to discover, like why exactly we have dermatoglyphics (those are fingerprints), what we do know about skin is scintillating.

Bacteria, fungi, viruses—these are just a few of the microbes that make you uniquely you. If it wasn’t for bacteria, we wouldn’t be able to breathe. The author notes that 80% of the air we fill our lungs with is actually nitrogen, not oxygen. Bacteria are the microbes that convert this into something we can use. Out of the 40,000 types of microbes floating inside you right now, only 1,415 actually lead to diseases. 

Viruses like the common cold may seem threatening, but science proves that they’re much more common than we think. In 1900 while studying tobacco plants, a botanist and the world’s first ‘virologist,’ Martinus Beijernick, discovered a microbe smaller than any bacteria. It was a virus. To have an impact on organisms, viruses must find a place within a cell. Fortunately for us, most viruses lodge in bacterial cells and have no outward impact on our health. There are exceptions to this, of course, and one of them is the infamous virus known simply as the ‘common cold.’ Despite valiant attempts at avoiding this virus through efforts such as washing your hands every time you touch a door handle or keeping hand sanitizer with you at all times, the cold is nearly impossible to elude. Immunity from the common cold is so difficult to attain because this virus is actually an accumulation of various kinds of viruses.

Bacteria can be equally challenging to get rid of despite the fact that some of them have a positive impact on your body. You’ve no doubt heard of penicillin and the story of its accidental discovery by the renowned Alexander Fleming in the 1930s, but you may not know that all penicillin produced today is derived from one moldy cantaloupe. It was still extremely difficult to make penicillin after its discovery, so in the 1940s, pharmaceutical researchers sent requests to fellow scientists to bring in any mold samples they found. A woman named Mary Hunt responded to this request, and pharmaceutical companies have been fueled ever since. This was a breakthrough in modern pharmaceuticals, but its side effects aren’t all promising to our health.

Unfortunately, antibiotics are prescribed to cure a wide range of infections, even those that are not bacterial and are proven to be unresponsive to such medicine, like viral maladies. Over time, our microbes learn how to resist these antibiotics until they’re practically useless. Increased resistance is in turn passed down through bacterial generations, which means that no one is immune from the impacts of a societal overreliance on antibiotics. Estimates predict that deaths due to antibiotic resistance will grow to ten million, making the issue a wide-reaching public health dilemma that people must become aware of.

The human body is both healer and protector, waging countless tiny wars inside us. As stewards of so much, we must be thoughtful and informed about what we put inside our bodies. Even something as small as a microbe can change us.

Weighing in at just three pounds, your brain uses approximately 20% of your energy to construct the world as you know it. Memory, color, reality, thinking—your brain dictates the functioning of each of these experiences. Inside your brain are cells called neurons, which are complete with an axon tail and dendrites that branch out from there. Neurons communicate with each other through synapses, and this determines intelligence. The cerebrum at the top of your brain is separated into two hemispheres with four regions called the frontal, parietal, occipital, and temporal lobes. Located at the back of your head right beneath what you see when you think of the brain is the cerebellum, which is also right near the brainstem. The brain helps us know our world, yet itself cannot be known.

Scientific studies and medical history prove that the region of your brain called the frontal lobe dictates a large portion of who you are as an individual. Human nature and personality cannot be confined to the brain, but science does tell us some pretty interesting things about ourselves. The frontal lobe is in charge of our emotional functioning, our thinking, and various other factors that comprise who we are as people. Unfortunately, scientists failed considerably before landing on this discovery. Before we knew the impact the frontal lobe has upon human personality and mental well-being, scientists developed a procedure meant to reduce ailments ranging from epilepsy and schizophrenia to OCD and general disobedience. In 1949, the doctor Walter Jackson Freeman adopted the methods of neurology professor Egas Moniz and popularized the frontal lobotomy throughout the United States. The process was excruciating and left people depleted of individuality and uniqueness.

Thankfully, the 1960s brought about Freeman’s retirement and the end of the lobotomy.  Neuroscience is still a long way from understanding the brain in its entirety (if that’s even possible), but it has progressed greatly from brutal and unethical medical procedures to practices that recognize the frailty and value of all human beings, no matter how quirky or disobedient.

Our blood has a rather winding history, much like the 25,000 miles of blood vessels that wrap and wind throughout our body. Within our blood are red cells, white cells, platelets, and plasma. While red blood cells are plentiful in our veins, delivering oxygen to the rest of our body, white blood cells make up less than 1% of our blood and are responsible for waging war on diseases, viruses, and any other threatening force that finds itself inside us. The majority of our blood consists of plasma, which delivers various nutrients and other necessary components throughout the body. Additionally, platelets help our blood clot when we experience cuts or other causes of bleeding. Each of these components is as necessary to blood as blood is necessary to life.

Now imagine a world in which esteemed doctors believed that in order to cure a patient of, say, a simple sore throat, one must drain the body of its blood, its life force and source of vitality. The author notes that medicine up until the 19th century was approached in a more holistic way. A simple cold signified a more widespread ailment, and in order to address the sickness in its fullness, it must be treated on the bodily level. That’s where the method of bleeding was introduced, along with various other treatments that expunged the body of any presumed illnesses. George Washington himself suffered an agonizing death through bleeding for a sore throat with the loss of 40% of his blood. Another American leader, the highly intelligent and fatally misled doctor Benjamin Rush was known as the “Prince of Bleeding,” and he administered bleeding treatments to many until his eventual death by bleeding as well. It’s easy to view these treatments as ridiculous, illogical displays of scientific ignorance, but at the time, very little was known about blood, and this procedure was lauded as a common cure-all. In all things, medicine included, darkness precedes clarity, and ignorance is a prelude to understanding.

Still, even today with our progressive science and medical know-how, there remain gaping holes in our knowledge. Currently, researchers like Dr. Allan Doctor at Washington University are experimenting with ways to create artificial blood through nitric oxide in hopes of avoiding the danger of real blood transfusions. Their efforts have proven unsuccessful so far, so doctors are simply limiting the number of blood transfusions to mitigate any danger. 

Despite the fact that there’s still so much left to improve upon, at least we’re miles away from the days of injecting humans with wine. And it’s good to hold onto our blood, too; we may need it, after all.

Despite the importance of exercise and rest to your overall bodily health, a majority of people are failing to get enough of either—only 20% of people engage in adequate regular activity, and the average amount of sleep has decreased from eight-and-a-half to seven hours per night. This is a plague with the potential to cancel any efforts you make to remain healthy through proper diet and nutrition. Movement and sleep simply cannot be replaced. In fact, our bodies were literally born to run. 

Due to the nuchal ligament located at the back of the skull and the neck, the mechanism that maintains the balance of your head, the author notes that we are made to run long distances. If that sounds like a little too much movement for you, don’t worry, walking can be just as effective to your health. After a long, immobile day at work, nothing is more welcome than stretching your legs for an hour outside, especially as the sun’s setting and the sky’s darkening. The author notes that daily walks decrease the rate of having a heart attack or a stroke by an astounding 31%. And it’s so easy, too. There’s no need to head out on a long run, unless you want to, of course—the benefits of that are even more plentiful. A study of joggers in Denmark showed that those who run often actually live five to six years longer than those who do not. While there may be several confounding variables in studies like these, the main point is inarguable. For better health, sit less, and move more. 

After that long walk, make sure to get a refreshing night’s sleep, too. Though we spend one-third of our lives curled up in bed, researchers have no clue why sleep is so integral to our health. Everyone knows that feeling of needing sleep so badly it’s as if a weight was placed on your eyelids. That sensation is called sleep homeostasis, the building desire to fall asleep due to an accumulation of chemicals in the brain. Imagine never being able to slip into that detoxifying, restorative state; illness, confusion, and general discomfort would abound. In 1986, a new disorder was uncovered in a family of people who literally could not sleep. This wasn't your typical case of pulling an all-nighter, either. Rather, it was a case of what is now known as fatal familial insomnia, a rare condition in which the victim’s thalamus is attacked by a protein called a prion, ending in her inevitable death due to complete exhaustion. While the condition is a rare medical anomaly, it attests to the absolute necessity of sleep.

Our bodies always know something we don’t. Science may not know why we need sleep, or exactly how much exercise is the optimal amount, but still, it proves that movement and sleep contribute greatly to our quality of life and health. So next time you’re feeling restless, listen to your body and go for a walk. You need it more than you know.

In 1937, Gunda Lawrence was perhaps the most fortunate cancer patient and mother alive. Both her sons had occupations in science, but one of them, Ernest Lawrence, was an esteemed physicist at a radiation lab which had access to a powerful X-ray machine. The two sons targeted their mother’s stomach and shot a deuteron beam into the core of her cancer. In a poetically moving and medically groundbreaking act, two sons healed their dying mother and started what is now known as radiation treatment. Stories like this abound in 20th century medicine. During this century, medical science experienced rapid growth. Though cancer became the second most common cause of death in the early 1900s, this shift only came about due to a decline in infectious diseases. Now, even cancer rates have seen a decline, dropping by 25-90% in the last 25 years. 

Despite greater life expectancy, more hygienic lifestyles, and various treatments for diseases and illnesses of all kinds, death is fundamental—our cells actually put the process of getting older on full display. In 1961, scientist Leonard Hayflick found that in experiments, cells appear to divide up until a certain point and then die shortly after. This is now known as the Hayflick limit, and it was further expanded to show that as cells are dividing, things called telomeres decrease to a particular length. Telomeres are DNA located at the bottom of chromosomes, and their function is also thought to be a possible link to finding a stable cure for cancer. Though the process of growing old was thought to be just another facet of human experience conquerable by science, our cells say otherwise.

Still, there are measures we can take to prolong our life and lengthen our telomeres. Kind, compassionate, and loving relationships are proven components of extending both the quantity and quality of your years on earth. Your son might not be a world-famous physicist, but lasting relationships with loved ones will prevent and heal a whole host of illnesses. 

The human body is truly a miracle, a puzzle that confounds the greatest scientific minds of today. Thankfully, we don’t need to understand it all to live—the body does that all for us.