The human body is a great, sweaty, fluid-filled machine, moving and mixing chemicals with precision and coordination, making everything from memories to mucus. Here we explore some of the complex, beautiful or just plain gross mysteries of how you function.

Skin

Your skin has four colors.  All skin, without coloring, would appear creamy white. Near-surface blood vessels add a blush of red. A yellow pigment also tints the skin. Lastly, sepia-toned melanin, created in response to ultraviolet rays, appears black in large amounts. These four hues mix in different proportions to create the skin colors of all different ethnicities.  It seems we were all black once (consistent with evolutionary fact of first humans in Africa). White skin was a result of humans moving away from the equator.

Laughing and yawning

The world laughs with you.  Just as watching someone yawn can induce the behavior in yourself, recent evidence suggests that laughter is a social cue for mimicry. Hearing a laugh actually stimulates the brain region associated with facial movements. Mimicry plays an important role in social interaction. Cues like sneezing, laughing, crying and yawning may be ways of creating strong social bonds within a group.

Brains and teeth?

Big brains cause cramped mouths.  Evolution isn’t perfect. If it were, we might have wings instead of wisdom teeth. Sometimes useless features stick around in a species simply because they’re not doing much harm. But wisdom teeth weren’t always a cash crop for oral surgeons. Long ago, they served as a useful third set of meat-mashing molars. But as our brains grew our jawbone structure changed, leaving us with expensively overcrowded mouths.

Cells have hair?

Cell hairs move mucus.  Most cells in our bodies sport hair-like organelles called cilia that help out with a variety of functions, from digestion to hearing. In the nose, cilia help to drain mucus from the nasal cavity down to the throat. Cold weather slows down the draining process, causing a mucus backup that can leave you with snotty sleeves. Swollen nasal membranes or condensation can also cause a stuffed schnozzle.

Puberty and the brain

Puberty reshapes brain structure, makes for missed curfews.  We know that hormone-fueled changes in the body are necessary to encourage growth and ready the body for reproduction. But why is adolescence so emotionally unpleasant? Hormones like testosterone actually influence the development of neurons in the brain, and the changes made to brain structure have many behavioral consequences. Expect emotional awkwardness, apathy and poor decision-making skills as regions in the frontal cortex mature.

Eggs

Thousands of eggs unused by ovaries.  When a woman reaches her late 40s or early 50s, the monthly menstrual cycle that controls her hormone levels and readies ova for insemination ceases. Her ovaries have been producing less and less estrogen, inciting physical and emotional changes across her body. Her underdeveloped egg follicles begin to fail to release ova as regularly as before. The average adolescent girl has 34,000 underdeveloped egg follicles, although only 350 or so mature during her life (at the rate of about one per month). The unused egg follicles then deteriorate. With no potential pregnancy on the horizon, the brain can stop managing the release of ova.

Brain needs food

Much of a meal is food for thought.  Though it makes up only 2 percent of our total body weight, the brain demands 20 percent of the body’s oxygen and calories. To keep our noggin well-stocked with resources, three major cerebral arteries are constantly pumping in oxygen. A blockage or break in one of them starves brain cells of the energy they require to function, impairing the functions controlled by that region. This is a stroke.

Bones are for storage

Bones break (down) to balance minerals.  In addition to supporting the bag of organs and muscles that is our body, bones help regulate our calcium levels. Bones contain both phosphorus and calcium, the latter of which is needed by muscles and nerves. If the element is in short supply, certain hormones will cause bones to break down upping calcium levels in the body until the appropriate extracellular concentration is reached.

Posture is important

Body position affects your memory. Can’t remember where you put your keys? Try mimicking the position/location you were in when you enter the house. Memories are highly embodied in our senses. A scent or sound may evoke a distant episode from one’s childhood. The connections can be obvious (a bicycle bell makes you remember your old paper route) or inscrutable. Episodes from your past are remembered faster and better while in a body position similar to the pose struck during the event.

You shrink every day

The body is taller in the morning than in the evening. You might want to schedule that basketball game for first thing in the morning. That’s because our bodies are on average about half an inch taller in the morning, thanks to excess fluid between our discs, which is replenished while we sleep. As the day goes on, and our bodies undergo the strain of standing, the discs get compressed and the fluid seeps out, so the body loses that small bit of extra height.