50 Wonderful Human Body Facts That’ll Answer A Lot of Your Questions – Part 6

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41 Involuntary Emotions

Involuntary Emotions

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.

42 Why Do Humans Have Allergies?

Why Do Humans Have Allergies?

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.

43 Sleep Amnesia

Sleep Amnesia

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.

44 Lanula


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.

45 Why did the Plague Stop?

Why did the Plague Stop?

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.

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46 Three Major Pandemics

Three Major Pandemics

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.

47 Grief is Exhausting

Grief is Exhausting

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.

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48 Rubbing the Pain Away

Rubbing the Pain Away

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.

49 Sexual Arousal

Sexual Arousal

We humans as a species are unique in our inability to tell whether or not a female is ovulating by just looking at them, which has made our sex drives grow to be a lot more complex. For animals, the evolutionary strategy to reproduce effectively is to “have sex when the female is in heat” or “have sex during mating season.”

For humans, the evolutionary strategy to reproduce effectively is to “have sex often to have a chance at making an offspring.” Therefore humans need to be convinced to have sex regularly or we would barely reproduce. That’s the reason why evolution has made humans to be sexually aroused when seeing other members of our species naked/copulating (porn).

Studies have also shown that men actually do find women more attractive when they are ovulating as women have been found to show some subtle signs while ovulating. Another study has also found that “ovulating women unconsciously buy sexier clothing to outdo other attractive women.” This apparently works both ways as studies have found that men who don’t masturbate, buildup semen, and naturally (though not deliberately) become more flirtatious.

50 Sleep Filter

Sleep Filter

When you are asleep, reticular formation (a set of interconnected neurons in the brain) modulates the passage of sensory input through the thalamus to the cerebral cortex. It decides what stimuli are important enough to be processed. The humming of electricity, the feeling of your underwear against your butt, and the smell of the wet dog in your house are ignored. It has determined that these things are not dangerous and you can ignore them. A siren passing in the distance, a bomb going off, or a bright flashing light will attract your attention because it is different and considered important. Some stimuli might wake you up but if it isn’t important enough you will fall back asleep without even remembering (a light turning on in the hallway or a dog barking). Others might keep you up for hours (a door slam, gunshot, or the smell of smoke).

It all depends on the type of stimulation and how important your brain decides it is for you to be awake.

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