1. Why do we sweat when we’re nervous?
Your body deals with a potential threat by going into fight-or-flight mode. This involves the part of your brain that controls basic functions, the hypothalamus, telling your adrenal gland to release a ton of hormones. One of these is epinephrine, also known as adrenaline, and is what gets your sweat glands going. The idea is that you’ll need to keep cool while you’re confronting the threat — even if it’s just giving a presentation.
2. Why do we blush?
This is another symptom of the fight-or-flight response. When you’re embarrassed, your body releases adrenaline. Your blood vessels then dilate in order to get more oxygen to your muscles by letting more blood through your veins. This has the unfortunate side effect of making your face look redder. Oh, and it’s an involuntary reaction, so there’s absolutely nothing you can do about it.
3. Why is the sky blue?
Sunlight looks white, but it’s actually made up of all the colours in the rainbow. When it hits Earth’s atmosphere it is scattered by particles in the air. Different colours of light have different wavelengths, and blue is the shortest, so it gets scattered most. That’s why the sky looks blue.
4. Why do we yawn?
You probably know that yawning is contagious. Seeing someone else yawn, or even just reading this sentence, might trigger you to yawn yourself. There are several theories about why we yawn in the first place but the latest — that we yawn to cool down our brains — seems to be sticking.
5. Why do humans not have tails anymore?
Simply put, we don’t need tails anymore. They were useful for balance when we used to walk along tree branches, but when we started swinging from them and, eventually, walking upright, we didn’t need a counterbalance anymore. An extra limb we don’t need is just using up energy, so once we no longer had a use for them our tails would have disappeared through natural selection over the next few millions of years.
6. Why do we get hiccups?
Hiccups happen when your diaphragm contracts. It’s a reflex, so you have no control over it. Your diaphragm sits under your rib cage and helps control your breathing. There are lots of causes of hiccups, but one of the most common is an irritation of your oesophagus or stomach.
7. Why do we grow two sets of teeth?
It’s all about size. Apart from looking absolutely terrifying, a full set of adult teeth would be too big to fit into a baby’s mouth. But they need some teeth, so milk teeth stand in until our jaws are big enough to accommodate full-size ones.
8. Why do we get dark circles under our eyes when we’re tired?
The dark bluish tint is caused by blood flowing through the veins just underneath your skin. When you’re tired, your body produces more cortisol and the volume of blood in your body increases. This increase is more visible under your eyes because of the thinner skin there.
9. Why do we cry when we’re sad?
Tears show others that you need support. Humans are the only species we know of that produce emotional tears and still cry in adulthood. One theory is that we cry instead of emitting sounds when we’re distressed, because making a sound would attract predators.
10. Why do we get bored?
A study published in 2012 defines boredom as “an aversive state of wanting, but being unable, to engage in satisfying activity.” Boredom comes about when we have difficulty paying attention to information, either internal (like feelings) or external (like what’s going on around us) and recognise this — but try to blame it on the environment instead.
11. Why do we laugh?
But laughter can also be used to exercise control over a group of people. Dominant individuals, like a boss in an office, are more likely to orchestrate laughter than their subordinates.
13. Why do we sleep?
We’ve long known that we need sleep to function properly, but exactly why we sleep and what happens while we’re sleeping has long been a mystery. A study that came out last year says that while we sleep our brains basically spring-clean themselves, using cerebral spinal fluid to flush out “molecular detritus” and harmful proteins that can lead to dementia if they build up. But the study was only in mice, and it’s as yet unclear whether the same thing happens in humans. Either way, it’s unlikely to be the full story.