🎄🔬Science-Translated Advent Calendar🔬🎄
24 days, 24 facts - perfect material for impressing (or annoying) relatives at the Christmas dinner table.
01
Your ear was once a jaw (in a way)
Two of the tiny bones in your middle ear (the malleus and incus) originally formed part of the jaw joint in early vertebrate ancestors.
Over millions of years, evolution repurposed these bones, transforming them into key components of the mammalian hearing system.
Biology rarely invents new parts, it remodels what is already there.
02
You technically have cancer
Right now, inside you, tiny cancer-like cells are appearing (and being eliminated) without you ever noticing.
Every day, billions of your cells copy their DNA.
Some of them make mistakes big enough to push them toward becoming cancer, but almost none of these ever turn into a tumor.
Why?
The moment a cell behaves suspiciously (dividing too fast, expressing the wrong proteins, ignoring signals) your immune system marks it for destruction.
Most “cancers” die before they even are cancers.
Disease begins only when one mutated cell manages to
hide, grow faster than the immune system can react, or
reprogram its surroundings to protect it.
03
You glow in the dark (a little).
The human body emits visible light, we’re just not sensitive enough to see it.
Every cell in your body produces energy using oxygen.
During this process, small amounts of that oxygen become excited, creating tiny flashes of light known as biophotons.
These flashes:
- follow your daily circadian rhythm
- are brightest in the face
- and peak in the late afternoon.
Some animals use bioluminescence to communicate, hunt, or mate.
04
You are more microbe than Human
Your body houses trillions of microbes (bacteria, viruses, fungi, archaea) living on your skin, in your mouth, and especially in your gut.
Your microbial cells rival or even outnumber your human cells.
For every human cell in your body, there’s roughly one microbe living alongside it. Together, they form your microbiome, an ecosystem so essential that some scientists call it another organ.
These microbes help you:
- digest food
- produce vitamins
- train your immune system
- protect against harmful bacteria
- and even influence your mood and behaviour
05
You replace your entire skeleton roughly every 10 years.
Every bone in your body is alive.
Right now, your skeleton is being broken down and rebuilt by two groups of cells:
- osteoclasts (the demolition team)
- osteoblasts (the construction crew)
Bone remodelling never stops.
It responds to stress, movement, nutrition, hormones, even sunlight.
The bones you have today are not the bones you had a decade ago.
This constant renewal allows your skeleton to:
- repair micro-damage
- adjust to new loads (like strength training)
- store and release minerals
- stay strong despite daily stress
Your bones may feel rigid, but biologically, they’re more like a highly active construction site.
06
Your muscles remember your workouts… even years later.
When you train, your muscles don’t just get bigger, they change how their DNA is used.
Strength training adds extra nuclei to your muscle fibers and leaves behind epigenetic marks that adjust gene activity.
Even if you stop training and lose the visible muscle, many of these molecular changes stay.
This means:
It’s easier to rebuild lost muscle than to build it the first time.
Your muscles literally store a biological memory of past workouts.
So yes, your former gym-self left you a gift.
07
Your brain cleans and edits itself while you sleep
When you fall asleep, your brain starts a night shift.
It actually shrinks slightly, creating more space for cerebrospinal fluid to wash through and clear out metabolic waste including proteins linked to neurodegenerative diseases.
But cleaning is only half the story.
During deep sleep, your brain also:
- strengthens important memories
- weakens or deletes irrelevant ones
- reorganises connections to make room for tomorrow’s learning
Sleep isn’t passive.
It’s maintenance, memory editing, and neural housekeeping, all happening while you lie still.
08
Your immune system remembers for decades.
Some vaccines, as well as some infections leave behind a biological memory that can last 40 years or more.
Inside your lymph nodes and bone marrow live long-lived memory B cells and plasma cells.
These cells don’t just float around waiting. They actively keep a record of past threats:
- the virus you met as a child,
- the bacteria you fought in school,
- the vaccine you got in your teens.
How does this memory actually work?
When your body fights an infection for the first time, it tests millions of slightly different immune cells to see which ones work best.
Most disappear again, but the winners are saved.
Some become memory cells, quietly patrolling your body for years.
Others settle into your bone marrow and keep making tiny amounts of antibodies in the background, like a smoke detector that never turns off.
If the same germ ever returns, these memory cells react within hours, long before you start feeling sick.
That’s why second infections are often milder, or don’t happen at all.
09
Your body makes alcohol every day
Even if you never drink, your body still produces small amounts of ethanol on its own.
How?
Inside your gut, bacteria break down carbohydrates and release tiny traces of alcohol (a process known as endogenous fermentation).
Your liver immediately detoxifies it, so you don’t feel anything.
In most people, these alcohol levels stay extremely low.
But there are rare cases where certain gut microbes overgrow and produce so much alcohol that people can actually feel intoxicated (a condition called auto-brewery syndrome).
10
Your bones make blood
Most people think of bones as hard, solid structures, but inside, they house one of the busiest factories in your entire body.
Your bone marrow produces:
- red blood cells (around 2 million per second!)
- white blood cells (your immune defenders)
- platelets (for clotting and healing)
This process, called hematopoiesis, runs nonstop from before you’re born until the end of your life.
The marrow inside your ribs, spine, pelvis, and long bones contains stem cells that can transform into any blood cell type your body needs, for more oxygen transport during exercise, more immune cells during infection, more platelets when you’re healing a wound.
Your skeleton isn’t just holding you up.
It’s keeping you alive from the inside out.
11
You get completely new skin every 4 weeks
Your skin looks solid and stable, but it’s actually one of the fastest-renewing organs you have.
Every minute, you shed around 30,000 dead skin cells.
Most of the dust in your home?
Yes, that’s (partially) you.
Meanwhile, new cells constantly rise from deeper layers of the epidermis, where they divide, flatten, link together like tiny tiles, fill with protective keratin, and migrate upward until they form the fresh barrier that replaces the ones you lose.
Within about 28 days, your entire outer skin layer has been swapped out for a new one.
You’re regenerating all the time. Quietly, invisibly, and without noticing.
12
Your sense of smell is directly wired into your memory
Smells don’t just “seem” nostalgic, they truly are!
That’s because your olfactory system is the only sensory pathway that goes straight into the brain’s memory and emotion centers without passing through the usual filters.
When you smell something:
- signals go directly to the amygdala (emotion)
- and the hippocampus (memory formation)
No other sense has this VIP shortcut.
That’s why a single smell (sunscreen, cinnamon, wet pavement) can instantly transport you to a moment you haven’t thought about in years.
Your nose is basically a time machine with scent triggers.
13
Humans can’t actually feel “wet.”
It feels obvious that we can sense when something is wet.
But biologically speaking, your skin has no receptors for wetness.
Instead, your brain senses wetness by combining different signals:
- temperature (wet things are often cold),
- pressure on the skin,
- movement across the surface.
Put these together, and your brain concludes: this must be wet.
That’s why:
- cold metal can feel wet
- warm water can sometimes feel dry
“Wet” isn’t a real sense.
It’s a clever illusion created by your nervous system.
14
Your tongue doesn’t have “taste zones”.
You may have seen the classic diagram showing sweet at the tip of the tongue, bitter at the back, and salty on the sides.
That diagram is wrong.
In reality, every taste bud can detect all five basic tastes:
sweet, salty, sour, bitter, umami.
Some areas are slightly more sensitive than others, but there are no strict zones where only one taste works.
What we call “taste” is actually a combination of signals:
taste buds on the tongue, smell from the nose, temperature and texture.
That’s why food tastes flat when your nose is blocked. Your tongue still works, but a major part of flavour perception is missing.
Taste isn’t mapped to zones.
It’s built from multiple senses working together.
15
You are slightly radioactive.
You might not feel it, but your body naturally emits tiny amounts of radiation, and that’s completely normal.
This happens because your body contains naturally radioactive elements, especially potassium-40 (K-40) and carbon-14 (C-14).
These atoms slowly decay as part of normal chemistry inside your cells.
The radiation is harmless and extremely weak, but sensitive instruments can measure it. Scientists even use this natural radioactivity to study metabolism and to date biological material.
It’s not something you feel or see, just a reminder that physics doesn’t stop at the skin.