40 Human Body Facts That’ll Fascinate & Disgust You – Part 6

Contrary to what most of us would like to believe, decision-making may be a process handled to a large extent by unconscious mental activity. A team of scientists has unraveled how the brain actually unconsciously prepares our decisions. Many processes in the brain occur automatically and without the involvement of our consciousness. This prevents our minds from being overloaded by simple routine tasks.

27. The need for resistance training for muscle growth is mostly a human trait. With appropriate genes, simply growing muscle without the training is not only possible, but takes fewer calories, so it is much more efficient and preferable by other species.

Exercise for the sake of exercise burns up a lot of calories which in other animals is best preserved for acquiring food, reproducing, etc. Humans engage in muscle building as a result of our societal evolution from that of hunter-gatherers where we were just like other animals of today. Division of labor has made food acquisition the least of our worries. So, we now have dedicated plenty of time and resources to working out to impress people (or most likely ourselves).

28. In countries with poor access to clean water, a lot of people suffer from water-borne diseases, and this leads to substantial morbidity and mortality, especially in young children. Healthy adults, however, in these countries have higher resistance to some pathogens compared to people who grew up in countries that have easy access to clean water, which explains traveler’s diarrhea.

29. Bacteria floating around in your mouth by and themselves are not strong enough to get through your enamel (hardest outer layer of the tooth), but when bacteria are left around long enough they begin to stick together to form a biofilm. This starts as a soft biofilm called plaque. Brushing your teeth or scraping it will remove this soft biofilm without much effort. In left untouched, this soft plaque begins to strengthen and hardens into tartar.

Tarter is solid and no matter how hard you brush, it will not come off. That’s why dentists scrape it off with special instruments. This is the reason why tooth decay can’t be prevented just chemically (mouthwash), it has to be addressed mechanically (brushing/flossing). Mouthwash is not a rip-off though, it’s just more supplemental. For an average person, fluoride mouthwash is best unless your dentist says otherwise.

30. Cancer cells are the result of mutations that disable the mechanisms that keep cell growth in check. Those mutations come from incorrect repairs to cell DNA, and those errors happen more frequently the more repairs take place. If the body is forced to do repairs often and faster (e.g. for smokers), it will make more mistakes.

The human body already has a number of ways to deal with cancer though. Cancer cells are produced in the body all the time but those cells have mechanisms in place to kill themselves if they become cancerous or they are obliterated by the immune system. It needs to get past both of those things and start reproducing out of control to become an issue.

Any intense activity that you are not used to can cause delayed onset muscle soreness. It does not hurt right after a workout but hurts usually a day later when you move the affected muscle. The current scientific consensus is that your nerves are actually responsible for this. Intense activity results in microscopic damage to the muscles, which is not intense enough to cause pain right away. The repair process of this damage involves some inflammation and immune cells, so to call them the muscle produces some signal chemicals and molecules that initiate repair. This also makes the neurons that innervate the muscles to become more sensitive to movement.

This does not happen that fast though (it takes time to make new proteins). Thus you are not sore right away because it’s not the neurons sensing damage but them becoming more sensitive to movement. This makes you move your muscles a bit less so that they can heal.

32. During the first three years of human life, bladder storage capacity increases disproportionately relative to body surface area. By four years of age, most children void five to six times per day. Development of bladder control appears to be a progressive maturation whereby the child first becomes aware of bladder filling, then develops the ability to suppress voiding involuntarily, and, finally, learns to coordinate muscles necessary to void voluntarily.

These skills usually are achieved, at least during the day, by approximately four years of age. Nighttime bladder control is achieved months to years after daytime control but is not expected until five to seven years of age.

33. There’s a reason it is difficult to sometimes suppress laughter or a smile. Facial expressions are closely linked to emotions. It is thought that the purpose of facial expressions is to convey emotions within a social group. Studies have shown that the link goes both ways, i.e., being happy can make you smile, and forcing yourself to smile can make you happier, which reinforces the idea that feeling emotions and exhibiting their signs are closely linked.

Emotions aren't entirely involuntary, but strong emotional reactions that are triggered by an external stimulus can be hard to override, i.e., controlling the physical manifestations of your emotional responses partly involves controlling the emotions themselves.

To add to this, emotional smiling and voluntary smiling (controlling facial muscles) are controlled by different centers in your brain. Researchers have observed that some people who have lost the ability to smile voluntarily because of a brain lesion can still smile due to an emotional stimulus that is not voluntary.

34. Allergies are caused by your immune system reacting to specific molecules. The human immune system has several varieties of antibodies (the parts that detect pathogens and cause immune reactions). There are five in fact: IgA, IgD, IgE, IgG, and IgM. IgE is the antibody that is associated with allergies (an overreaction by this antibody).

Interestingly, IgE is only found in mammals, making it ‘young’ (on the evolutionary timeline) compared to those found in fish, reptiles, and insects. Part of the theory behind allergies considers that IgE is ‘new’, its cutting edge, and could be considered a work-in-progress (in evolutionary terms).

Interestingly, IgE also fights intestinal worms, so some experts believe that parasitic worms (Helminths) are necessary for the immune system to properly regulate itself, as we humans evolved alongside them. The parasite reduces the amount of IgE in the body to stop the body from attacking itself. There are ongoing tests, where doctors are trying to treat immune disorders (such as Lupus, Rheumatoid Arthritis, and psoriasis), and common allergies (such as hayfever) with parasites. Results have been fairly hopeful.

35. There is a reason you don’t remember falling asleep. Falling asleep is a very smooth transition. You make a transition from awake to pre-sleep, light sleep, slow-wave sleep, and then to REM sleep. Memory formation depends heavily on changes. We are most likely to remember something new rather than something that doesn't really alter over time. Falling asleep is a rather slow change so there is limited need to remember it.

Secondly, pre-sleep goes hand in hand with decreased perceptual awareness. With decreased awareness, there is just less content to store. With the decreased perceptual awareness we switch to an internal reflective state, thinking of things rather than learning new things. So you start to think about other things and then there is nothing new to remember.

The white-colored, half-moon-shaped structure at the base of our fingernail is called the ‘Lunula.’ This forms part of the nail matrix, basically the region that’s responsible for the growth of the entire fingernail. The rest of the nail matrix lives under your skin at the base of your fingernail.

Damaging the nail matrix will screw with the growth of the entire nail. You'll sometimes see lines called Beau's Lines if you damage the lunula.

By looking at the distance of these lines from the nail matrix, you can tell approximately how long ago the injury happened. Fingernails grow ~1mm per month and are fully replaced every 6 months. So an injury that has grown halfway up the nail (~3 mm) is about 3 months old.

37. Someone asked us this question, “Why did historical diseases like the black death stop?” The answer is that people still get bubonic plague in some parts of the world, just not on an endemic scale. Perhaps because of sanitation, it doesn’t spread like it used to, but it has not completely been eradicated.

In general, infectious diseases never keep going forever at a high rate, because as soon as the number of healthy individuals drops significantly (due to infection, immunity, or death), transmission rate drops and so does the supply of fresh host to spread to. This is why deadly diseases only come in sudden waves and die down.

The key to controlling any infectious disease is to reduce the number of susceptible people by any means possible (vaccine, quarantine, or getting them all infected). It’s called the SIR model (Susceptible-Infected-Removed). It’s the basis for all modern infectious disease models.

38. Everyone knows about the Second Plague Pandemic (which includes the Black Death) but there were three major pandemics in total. The First Pandemic spread in the 6th and 7th centuries which killed up to 40% of the population in Constantinople and Europe. It happened during a period of scarce historical record so it's now mostly forgotten but it devastated the Byzantine Empire.

The Second Pandemic began with an epidemic in Mongolia in the 1330s and then it spread to Europe through the Silk Road. It was first recorded in Europe in 1347, resulting in a 6-year period called the Black Death where an estimated 30% to 60% of Europeans died. The end of the Black Death didn't result in the end of the Second Pandemic as the bacteria became endemic in Europe and continued to cause deadly Bubonic plague epidemics for centuries to come. During the 16th to 17th century, there was a major plague outbreak in Paris, on average once every 3 years. The classic plague doctor outfit wasn’t invented until 1619 and used until 1656. The last major British plague epidemic was the Great Plague of London from 1665-1666 which also spread to the surrounding areas. This resulted in Newton being sent home from the University of Cambridge and quarantined. 1666 was Newton’s annual mirabilis when a bored 23-year-old Newton came up with numerous theories and experiments which changed the history of science.

The Third Plague Pandemic lasted from 1855 until 1960 in India and China but didn't really spread to Europe. It caused the death of 12 million people, 10 million in India alone.

Some researchers also believe that the Bubonic Plague might also have been responsible for the Neolithic decline of the human population in Europe 5000 years ago.

39. People often wonder why grief is physically exhausting. We often miss the fact that emotions aren’t just feelings, they’re biochemical reactions. Grief is induced by and induces a lot of stress chemicals (like cortisol) and you don’t get enough of the happy chemicals and endorphins. Your body doesn’t function well in this state.

Then there's also the fact that your brain is very energy-hungry, so any time you use it a lot, you will feel tired, e.g. studying, or jobs that require frequent decision-making. The simple act of thinking about the person you miss all the time uses up a lot of energy. On top of that, people who are grieving often don't replenish the energy used because they are sleeping and eating less.

40. There’s a reason why rubbing the area where you are hit makes it feel better. Nerves in the skin can feel stretch, temperature, pain, and pressure; and you mostly can only feel one of them at a time. Pressure beats them all, similar to a game of rock, paper, and scissors. When you cut yourself and squeeze the cut finger hard, you feel the pressure but not the cut. Rubbing hard is a form of pressure, which then beats out the pain.