Yawns Freeze Your Brain

CHAPTER 1.

OUR BODIES

(or Yawns freeze your brain)

What? Yawns freeze your brain?

Sort of, but perhaps not in the way you think. There is no ice involved but some scientists believe yawning makes your brain cooler. This helps keep it at its optimum functional temperature - heat is released as we yawn - and studies show people yawn more in summer. However, there is no actual scientific consensus on yawning. A more popular theory than the brain-cooling suggestion - and the only one that takes into account the fact that we yawn most when we are sleepy - is that yawning helps keep us awake when we would otherwise have nodded off during boring or passive activities. It stimulates the carotid artery in the neck, increases both heart rate and blood flow to the brain and releases hormones that keep us awake. It also dampens our eyes, which stimulates us to wipe them. Because we rarely yawn when on the move, this suggests yawning is only necessary when we are passive. However, other researchers have noted that we will yawn before undertaking strenuous exercise or before an exam, when blood flow to the brain is equally desirable. Lastly, yawning helps reduce pressure and blockages in the Eustachian tubes in our ears. But this might just be an unintended consequence, because swallowing is a more effective means of doing this.

Why is yawning contagious?

There seems to be more agreement on this. In primitive societies, where it made sense for most people in groups to sleep at the same time and disturbances were kept to a minimum, yawning indicates that sleep time is approaching. This is backed up by the fact that we yawn if we see a family member or friend do it, but more rarely if we see a stranger yawn. The empathy of yawning draws social groups closer together and synchronises the collective mood. Other animals yawn too but contagious yawns are only found in more social animals, such as chimpanzees and lions, which gives weight to the empathy/synchronising theory. Even more interesting is that some animals, including dogs and elephants, are prone to catching yawns from humans. Chimpanzees will even yawn when they see a robot yawning. We are still figuring out why.

The wonderfully named Sprague-Dawley rat yawns about 20 times an hour, as opposed to only about twice an hour in other rat species. Studies show that the rat's facial temperature falls every time it yawns, allowing it to cool its body in hot weather.

Why do we have eyebrows?

They serve a very practical function by stopping sweat running into our eyes and stinging them when we are exercising or on hot days. But eyebrows serve another purpose: we use them to express our emotions, and it's why the hair of human eyebrows is usually noticeably different to our skin colour - to make them stand out. Surprise, annoyance, happiness, confusion, and so much more, can be displayed using our incredibly mobile eyebrows. For our ancestors, needing to know from a distance whether an individual or a group had hostile intentions or otherwise was an important evolutionary benefit. Anthropologists refer to the 'eyebrow flash' - a rapid up-and-down movement that also opens the eyes and conveys recognition and acceptance.

Tests in laboratory conditions during which speech is forbidden have shown that people with no eyebrows, or those whose eyebrows are immobilised, have greater difficulty conveying their emotions. Think twice before getting those Botox injections.

Why do we have fingerprints?

So the police can solve crimes. Well, it helps, of course, but obviously that was never their primary purpose. Fingerprints work much like the tread on a car tyre, helping us to grip things. Smooth surfaces are great for this in dry environments but are useless in wet ones. Our fingers have evolved to have raised and depressed areas that channel the water away from our finger ends, allowing us to hold onto things that might otherwise slip from our grasp.

Myth: Your fingerprints are unique.

It would appear that's not the case, at least not between each person's individual fingers. It's long been believed that the prints on all ten of our fingers are as unique as they would be if each finger belonged to a different person. But recent research shows that might not be true. In 2023, Columbia University ran a study using artificial intelligence which, when presented with two fingerprints, correctly predicted whether they came from the same person or not 77% of the time. Fingerprints from different fingers of the same person shared strong similarities.

Toe prints are as unique as fingerprints.

Nipples also leave unique patterns in the way fingerprints do. However, most criminals fail to remove their shirts at crime scenes so this knowledge, while intriguing, is of little use to the police.

How many atoms are there in a human body?

An astonishing 7,000,000,000,000,000,000,000,000,000 or thereabouts (7 octillion).

Atoms contain a lot of space. If all this space was removed our bodies would fit into a cube about 1/500 of a centimetre on each side.

Every atom in your body is billions of years old. And we really are made of stardust. Some atoms, such as hydrogen, were created in the Big Bang 13.8 billion years ago. Other, heavier, elements, such as oxygen, were created in early stars. When these stars exploded, they created even heavier elements, such as iron and magnesium. Because our body is composed of all of these and more, we are all pretty ancient.

There are around 20 elements that make up our bodies - of these 12 weigh in total more than four grams each. In the average human male, they are broken down like this:

Oxygen 52 kilograms

Carbon 14.4 kilograms

Hydrogen 8 kilograms*

Nitrogen 2.4 kilograms

Calcium 1.12 kilograms

Phosphorus 880 grams

Sulphur 200 grams

Potassium 200 grams

Chlorine 120 grams

Sodium 120 grams

Magnesium 40 grams

Iron 4.8 grams

(*Most of our body's atoms are hydrogen, but hydrogen is very light, which is why it's only third on the list.)

Why do we cry?

It's not just to clog up your nose, cause your make-up to run and embarrass you in public. It seems there are a number of reasons why humans cry and one of the most important, counterintuitively, is to make us feel better. Crying releases oxytocin (sometimes known as the love hormone, which plays a role in social bonding) and endorphins, the feel-good chemical messenger, which help to relieve emotional anguish, along with physical pain. That's why we cry when sad or distressed too. There are also social reasons why we cry. It indicates we require help or support, and showing vulnerability elicits sympathy and compassion. Similarly, we also cry to express our own sympathy. If a friend has suffered a bereavement, we may find ourselves crying alongside them. Look at how many people cry at funerals, not all of them closely related to the deceased. Of course, not all crying is a response to pain or distress. We can cry when we are happy or in love or by watching a child achieve a goal. Researchers believe that crying helps us process and categorise our emotions, whatever they may be.

Why do we laugh?

Because it's preferable to crying? Well, often it is, but neither seem to be a choice. We actually start laughing (and crying) before we can talk, so it obviously has a social function. Laughter signals to others that we are connecting with them. We are far more likely to laugh when we are in a group, especially during activities like watching comedy on TV, but less likely to do so alone. Interestingly, people speaking in social situations laugh more than those listening to them, hoping, apparently, that by doing so the listener will warm to them. Not only that, but in tests listeners could discern a difference between the laughter generated between strangers and that generated between friends. This shows that some laughter is forced in order to make a new person like you or to show you are no threat. It exhibits an offer of friendship. There are also physical benefits to laughter. It increases our oxygen intake and affects our heart rate and blood pressure (both up and down, which simulates exercise). Perhaps significantly, it releases endorphins - those feel-good chemicals again.

Why do we smile?

Much like laughter, smiling is a social signal, which communicates to people around us that our intentions are positive and unthreatening, and we are in good spirits. However, research has shown that sometimes smiling can be used as an attempt to cover up fear. Martial arts exponents who smile before a contest are more likely to lose. Other research has shown that genuine smiling involves wrinkling around the eyes which tends to be absent with feigned smiles. So don't forget to wrinkle next time the boss makes another terrible joke.

Why do we have goosebumps?

Goosebumps, or goosepimples, are a remnant from our evolutionary predecessors. They occur when tiny muscles around the base of each hair tense, pulling the hair more erect. This would have helped to keep us warm if we were still covered in fur, fluffing up our coats, making them better insulators.

We get a similar response when we are scared. This is because lots of mammals fluff up their fur when threatened, to look...