Different scientists see the human body in different ways. Physicians see us as collections of cooperating systems that complement each other and sustain health. To an engineer, the body is a system of support structures and musculature that distributes force from place to place. Geneticists see us in terms of the information carried in our DNA.
Each of these views is accurate but limited. The human body is a miracle of evolutionary engineering that displays a confounding array of fascinating structures and behaviors.
Here are some of the most unlikely and interesting facts about the human body.
#1 You Are Mostly Bacteria
The human body is made up primarily of bacteria and other one-celled organisms.
Yes, you read that correctly. Of all the cells in our bodies, only 10 percent contain human DNA. The other 90 percent are bacteria and other one-celled organisms.
What is even more amazing is that each and every human being carries a special unique concoction of bacterial cells depending on location, diet, hygiene and many other factors. We receive the largest portion of bacteria from our mothers during birth, through breast-feeding and via contact with her skin. But we continue accumulating bacteria throughout our lives.
We think of bacteria as harmful, but that’s not true. The bacteria and other microbes within human bodies help us use the energy and nutrients in the food we eat, keep our immune systems functioning properly and may have even contributed to our own genetic heritage.
Which brings us to our next interesting fact…
#2 About 40 of Our Genes Are Bacterial in Origin
Researchers sequencing the human genome have been surprised to discover 40 genes that are shared exclusively between human beings and bacteria.
Scientists use common genes to help track evolutionary change over time. Species that share many genes are assumed to be closely related. The earlier genes entered the genetic make-up of a species, the more descendant species will have the gene.
But in this case, scientists found genes that are present in certain bacteria – and nowhere else except in human beings. Other mammals don’t have the genes. Our closest relatives among the primates don’t have them.
How these genes came to be part of the human genome is a mystery. Some scientists argue that they must have been part of humanity since very early in our evolution, while others say the existence of the genes suggests a mechanism that allows genes to jump from one organism to another via “lateral transfer.”
Scientists continue to study the issue. If bacterial genes can be swapped into the human geneome, that would open many doors for fighting disease and maintaining health. Some studies suggest that lateral transfer is an ongoing process, particularly in cancer cells, but more research is needed.
#3 We Have a Third Eyelid
This is a particularly strange one. We human beings have, or more accurately used to have, a third eyelid.
We lost the muscles in that area over time, but we still have the semi-transparent eyelid. It is called a nictitating membrane and you can still see it when you look at yourself in the mirror. It’s that pink bit right in the corner of your eye closest to your nose.
Nictitating membranes are common among fish and reptiles. They give delicate eye tissues some protection underwater while allowing the animals to remain alert to the existence of predators. Mammals like beavers and manatees have retained functional nictitating membranes to protect their eyes will underwater. The vestigial nictitating membranes present in land mammals is interpreted by scientists as evidence that their evolutionary ancestors once lived in the water.
#4 Sleep Cleans The Brain
When we are awake, our brains produce toxic waste products. When we are asleep, our brains take out the trash. This explains why the “sleeping” brain and the “awake” brain use just the same amount of energy.
Here’s how it works: The cells inside the brain shrink while we sleep to make it easier for the spaces around them to be cleaned. A liquid called cerebrospinal fluid flushes the brain and transfers the toxins into the bloodstream. The toxins are then carried to the liver for detoxification.
This may help explain our next interesting fact about the human body…
#5 We Can Last Longer Without Food Than Sleep
While we do not know how long a human can last without sleep before dying, we do know that after about 10 days we start losing the ability to function properly. We start to hallucinate visually and physically. We lose the ability to connect words into sentences. We lose weight. Our memory begins to malfunction.
We can see many of these effects within just a few days of sleep deprivation.
How long can we last without food? Depending on how much muscle and fat you have, you could last up to about 2 months without food. You will need plenty of water, however.
#6 We Use 100 Percent of Our Brains
I’m sure you’ve heard the old myth suggesting that we use only 10 percent of our brains. That’s exactly what it is, a myth.
Scientists aren’t sure how this myth came about, and they don’t really care. Every day specialized brain scans provide more scientific proof that every region of the brain has a specific function.
Still, the myth keeps circulating. It even serves as the basis of movies, including 2014’s “Lucy.”
Don’t be alarmed. As depressing as it may be to admit, you are using 100 percent of your brain.
#7 We Have More Than Five Senses
We all learn about the five senses in grade school. Can you name them? Smell, sight, taste, sound and touch.
But that list is far too short. Depending on who you ask (scientists argue just like real people), we have many, many more senses.
This list from (www.todayifoundout.com) presents 18 possible senses:
- Sight: This technically is two senses given the two distinct types of receptors present, one for color (cones) and one for brightness (rods).
- Taste: Some people argue that our sense of taste is actually five senses, since we sense sweet, salty, sour, bitter and umami tastes distinctly. Most people refer to taste as a single sense, however. You never heard of umami? Umami receptors detect the amino acid glutamate, which is a taste generally found in meat and some artificial flavorings. The taste sense, unlike sight, is based on chemical reactions.
- Touch: This has been found to be distinct from pressure, temperature, pain and even itch sensors.
- Pressure: Researchers say our sense of pressure is distinct from the “touch” senses that feel pain, heat and other phenomena.
- Itch: Surprisingly, this is a distinct sense from other touch-related senses.
- Thermoception: This is our ability to sense heat and cold. Some scientists argue that this, too, is more than one sense. This is not just because of the two hot/cold receptors in our nervous system, but also because there is a completely different type of thermoceptor, in terms of the mechanism for detection, in the brain. The thermoceptors in the brain are used for monitoring internal body temperature.
- Hearing: Detecting vibrations along some medium, such as air or water, that is in contact with your ear drums.
- Smell: Yet another of the senses that detect chemical reactions. This sense combines with taste to produce flavors.
- Proprioception: This sense gives you the ability to tell where your body parts are relative to other body parts. This sense is one of the things police officers test when they pull over someone who they think is driving drunk. The “close your eyes and touch your nose” test is testing this sense. This sense is used all the time in little ways, such as when you scratch an itch on your foot. Did you notice you can do that without glancing down to look at your foot and position your fingers? That’s proprioception.
- Tension: Tension sensors are found in your muscles. They allow the brain to monitor muscle tension.
- Nociception: The experience of pain. This was once thought to be the result of overloading the sense of touch, but it turns out this isn’t the case. Pain has its own unique sensory receptors. There are three distinct types of pain receptors: cutaneous (skin), somatic (bones and joints) and visceral (body organs).
- Equilibrioception: This is the sense that allows you to keep your balance and sense body movement in terms of acceleration and directional changes. This sense also allows you to perceive gravity. The sensory system for equilibrioception is found in your inner ears, in the vestibular labyrinthine system. Anyone who’s ever had this sense go out on them on occasion knows how important equilibrioception is. When it’s malfunctioning, you literally can’t tell up from down. Moving from one location to another without aid is just about impossible.
- Stretch: The nervous system’s stretch receptors are found in such places as the lungs, bladder, stomach and the gastrointestinal tract. A type of stretch receptor that senses dilation of blood vessels is also often involved in headaches.
- Chemoreceptors: These trigger an area of the brain’s medulla that is involved in detecting blood-borne hormones and drugs. It also is involved in the vomiting reflex.
- Thirst: This sense more or less allows your body to monitor its hydration level so you know when you need a drink.
- Hunger: This sense allows your body to detect when you need to eat something.
- Magentoception: This refers to the ability to detect magnetic fields, which is principally useful in providing a sense of direction when detecting the Earth’s magnetic field. Unlike most birds, humans do not have strong magentoception. However, experiments have demonstrated that we are able to detect magnetic fields, if weakly. The mechanism for this is not completely understood; it is theorized that this has something to do with deposits of ferric iron in our noses. This would explain why people who are given magnetic implants have much stronger magnetoception than people without such implants.
- Time: Scientists argue over this one all the time. No single mechanism or sensory system has been found that allows people to perceive time. However, experimental data has conclusively shown humans have a startling accurate sense of time, particularly when younger. The mechanism we use for this seems to be a distributed system involving the cerebral cortex, cerebellum and basal ganglia. Long-term time-keeping seems to be monitored by the suprachiasmatic nuclei, which are responsible for circadian rhythm. Short-term time-keeping appears to be handled by other cell systems.
That list of 18 senses is by no means comprehensive. A table at Meditation 24-7 explains how we might have as many as 33 senses: color, red, green, blue, hearing, smell, sweet taste, salty taste, sour taste, bitter taste, umami taste, touch, pressure, cutaneous pain, somatic pain, visceral pain, rotational acceleration, linear acceleration, proprioception, muscle stretch (for Golgi tendons), muscle stretch (for muscle spindles), heat, cold, arterial blood pressure, central venous blood pressure, head blood temperature, blood oxygen content, cerebrospinal fluid pH, plasma osmotic pressure (thirst), artery-vein blood glucose difference (hunger), lung inflation, bladder stretch and full stomach.
Scientists are unlikely to resolve this issue any time soon, especially since they are unable to define exactly what they mean by the term “sense” anyway. But in any event, the list of five senses we were taught in grade school is clearly too short.
#8 The Brain Loses Focus After 90 Minutes
Here’s a great excuse for procrastination: Your brain legitimately needs a break. There is no better excuse than one that is backed by scientific evidence!
The cycle of brain exercise and relaxation is called the ultradian rhythm. It is much like the cycle we go through as we sleep, with periods of peaks and troughs.
Every person’s ultradian rhythm is a bit different, but on average the brain can focus for about 90 minutes before it needs a 20-minute break. Then it can focus for another 90 minutes.
#9 Without Saliva You Cannot Taste
We all know that without saliva we cannot effectively break down our food, but did you know that without it you also wouldn’t be able to taste food?
You can prove this by doing a simple experiment. Dry off your tongue with a towel and put some salt on it. You won’t be able to taste the salt until your mouth generates some saliva. Really!
#10 It is Possible to Hear Color
Synesthesia is a phenomenon where stimuli that we normally experience through one sense are experienced through another. To put it simply, two senses become one. So, a person might hear a smell or taste a color.
There are about 60 different types of synesthesia. Women are three times more likely to experience it than men. It is also more common in left-handed people.
It is thought that about one in every 2,000 people has synesthesia, and many people don’t know it. They think everyone experiences the world that way!
#11 There are Different Types of Tears
Tears of happiness and tears of cooking onion soup not only feel different, they actually are different tears. In fact, scientists say our bodies produce three different types of tears: psychic, basal and reflex tears.
Psychic tears are those created by happiness, sadness, anger and other intense emotions. Basal tears provide lubrication for the cornea. Reflex tears come as a response to cutting onions or other irritation.
Curiously, the three kinds of tears have difference chemical composition. Scientists can distinguish the three kinds of tears by examining them under a microscope.
#12 Your Stomach Blushes Too
When you experience feelings of embarrassment or excitement, your body releases a hormone called adrenaline, which helps to prepare you for stressful or highly emotional situations. Adrenaline dilates the blood vessels, improving blood flow and oxygen delivery to body tissues. This makes the veins in the face, the stomach and the rest of the body have more oxygenated blood flow…which makes them take on a pink or reddish color.
#13 It’s Not You, It’s Your Bacteria
Sweat doesn’t have a smell.
Your body is covered with once-celled organisms, however – primarily bacteria that live on the skin, feeding on the proteins and lipids in your sweat. It is these bacteria that give your sweat that distinctive smell.
The bacteria feed on the yummy stuff in your sweat and chomp on some of your dead skin cells before they release waste by way of acids. These acids smell bad. So blame it on the bacteria!
Just Scratching the Surface
The human body is a carnival of chemical processes, unlikely structures and delicate systems. I hope you’ve enjoyed this tour of some of the interesting, bizarre and odd truths of being human…our selection of crazy, hard-to-believe-but-interesting facts about the human body.
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