Ever wondered why we cry, what earwax is for and if we can smell other people's emotions? In a fascinating look at what goes on between our ears, physician and philosopher Raymond Tallis explores the secret world of the human head
• BIRTHS & BEHEADINGS
The human head is formed after only eight weeks in the womb
The construction of a human head, one of the most complex structures in the natural world, takes place astonishingly quickly.
After only eight weeks in the womb, billions of cells have already formed themselves into a brain, highly developed eyes and ears, a recognisable face complete with tongue, mouth and nose, a skull and organised facial bones.
Once fully developed, the human skull can be remarkably tough - as was demonstrated in 1997 by strongman John Evans on the BBC's National Lottery Live show.
He balanced 101 bricks, weighing 416lb, on his head and managed to keep them there for ten seconds.
Such resilience is not confined to the skull. The muscles and vertebrae in the neck are also very tough, which makes beheading someone far from the easiest method of killing.
It took three blows to hack through the neck of Mary, Queen of Scots when she was executed in Fotheringay Castle in 1587.
An assistant held her hair to prevent her from moving.
The result was, as always, extremely gory, given that large arteries and veins, providing succour to the head, were severed.
Once cleaved from the body, a hairless human head weighs an average 11lb - roughly the same as a ten-pin bowling ball - and accounts for around 8 per cent of our total body weight.
A FUNNY BUSINESS
The real business of breathing is done in the lungs - the head is only a convenient throughway to let oxygen into the body.
Yet for a structure that has a passing interest in air, the head does an impressive number of things with it, from sneezing to speaking.
One of the most mysterious is laughing. This seems to be the most anarchic of all human activities yet giggles, titters, shrieks and belly laughs all conform to strict rules.
Each laugh has its own distinct "signature" - made up of short-vowellike notes, not more than a tenth of a second long.
These are repeated at regular intervals about a fifth of a second apart.
Once a laugh has started with a particular vowel sound, it tends to stick to it.
The sound may be "ha-ha-ha" or "ho-ho-ho", but not "ha-ho-ha-ho".
There seems to be resistance to such acoustic mongrels. Laughter can be infectious, as was illustrated in 1962, when three girls at a boarding school in Tanzania were stricken with bouts of uncontrolled mirth for hours on end.
Soon nearly half of the 159 boarders were affected, laughing for up to 16 days at a time.
The school was closed and the children sent home, but this resulted in the condition spreading to entire villages and towns.
No one died during this two-year outbreak of what appears to have been mass hysteria, but there was much agitation, exhaustion and interference with daily life.
Under normal circumstances, we laugh 30 times more frequently when we are with others than when we are alone.
As to why we laugh, no one knows, but scientists think they have solved one riddle at least - our inability to tickle ourselves.
Self-tickling doesn't work because the brain tends to suppress sensations caused by the body's own movements.
"This leaves it free to concentrate on its real job, which is to deal with unexpected stimuli from the outside world, and means that those entirely expected sensations of self-tickling are scarcely registered.
While people of European and African origin usually have earwax which is wet and honey-brown, a genetic mutation thousands of years ago ago resulted in most Asian people - as well as native Americans and Inuits who have Asian origins - developing earwax which is dry, flaky and grey.
Indeed, it has proved possible to track human migratory patterns, such as those of the Inuit, by looking at earwax type.
Whatever its colour, this mixture of sweat and secretions from the sebaceous glands performs many useful functions.
Propelled by our jaw movements, it washes out dirt and dust from the ear canal.
It also lubricates the skin lining within the canal, preventing it drying up and getting itchy, plus it has anti-bacterial and anti-fungal properties.
• NOSING AHEAD
Our nose plays a bigger part in our lives than we think
Our noses play a greater part in our lives than we realise.
Though we may not register it with our conscious minds, we can smell, for example, the emotions such as fear, contentment and another person's state of sexual arousal.
Women are better at this than men. Tests show women discriminate more reliably between armpit swabs taken from people watching "happy" and "sad" films.
Our ability to smell depends on the olfactory membrane at the back of the nasal cavity, which is the size of a postage stamp, but contains 10 million receptors. (Dogs, for whom smell is much more than recreational, have a billion or more receptors.)
Within this membrane, there are 1,000 different types of receptor cells which can respond to more than one smell, enabling us to recognise more than 10,000 odours, scents, fragrance and pongs.
• LIFE'S ONE BIG YAWN
Yawning is just as contagious as laughing
THE unborn child begins yawning after just 11 weeks in the womb.
Once born, each of us will yawn an average 250,000 times before we breathe our last.
The most plausible explanation is that this endless jaw-stretching is a protective reflex that maintains lung inflation.
It prevents the bubbles in the lung sponge - the so-called alveoli, where the exchange of oxygen and carbon dioxide takes place - from collapsing.
Yawning is as contagious as laughing. Research suggests that within five minutes of seeing someone yawn, 50 per cent of people will do the same.
Even reading about the subject can provoke an involuntary yawn. Can you feel one coming?
• RED FACES ALL ROUND
ONE facial feature over which we have no control is blushing.
We might ask why this is limited to the face - for example, why do our bottoms not blush when we are embarrassed?
The answer is that the blood vessels of the face are denser, wider and closer to the surface than those in other parts of the body.
As to why some people blush far more readily than others, this has proved much harder to investigate because of the difficulty of prompting cheek-reddening under experimental conditions.
One research project involved showing suggestive material to a series of young females.
There was not a blush in sight. Yet when they were thanked for their help at the end of the abandoned session, they apologised for their unco-operative cheeks and blushed scarlet.
A possible explanation for blushing is that it is a non-verbal means of saving face - admitting we are in the wrong before others criticise us.
This is backed by studies showing that people react less harshly to mistakes when the perpetrators blush.
• BREAKING A SWEAT
The forehead is one of only a few places on the body - along with the armpits, palms of the hands and soles of the feet - where we experience "emotional" sweating.
Unlike thermal sweating, which regulates our temperature and occurs over most of the skin, this is a reaction to fear, anger or stress.
Its mechanism is not well understood, though we are so familiar with it that the phrase "breaking out in a cold sweat" is commonly used to describe acute anxiety.
One theory suggests that cooling the body in this way allows it to burn more energy - as one might need to do in a frightening situation - without getting over-heated.
This is fine if the appropriate response is fight or flight, but perspiring profusely only adds to our embarrassment when we find ourselves rooted to the spot with horror at some gaffe.
• FACING THE FACTS
The human face can produce up to 3,000 expressions
Drawing on 43 muscles, we are capable of producing more than 10,000 facial expressions.
Up to 3,000 have a recognisable meaning to other people, but seven basic emotions are shown on the face in the same way in every culture: sadness, anger, surprise, fear, enjoyment, disgust and contempt.
These are innate, not learned; which explains why people who are born blind use the same facial expressions for each of these seven emotions as sighted people.
• SEEING IS BELIEVING
When our ancestors began walking upright four to eight million years ago, the elevation of the head gave an advantage to two of the senses - which worked over a long distance: vision and hearing.
It increased their importance over touch, taste and smell, which work only when we are close to what we are sensing.
As a result, vision today accounts for about 90 per cent of the information we acquire about the world through our senses.
Given the importance of our eyes, it makes sense that we produce tears to keep them moist, grit-free and uninfected.
But what about the tears which flow when we are feeling emotional - whether it's very sad or extremely happy?
Such tears are clearly central to humanity's understanding of itself, but still we understand little about their purpose.
Some researchers have pointed to the fact that emotional tears are different to ordinary tears in their chemical composition, being richer in substances such as manganese and protein.
But the idea that they may somehow help us get rid of stress-related toxins is unconvincing.
The kidneys seem better equipped for that job and emotional crying seems designed to deal with toxins of the soul rather than those of the body.
Whatever its hidden benefits, crying is not always valued in this country.
We expect the statesman to wipe away a single tear with a leather-gloved finger as he places the wreath at the Cenotaph rather than work his way through box after box of Kleenex.
Other cultures are more Spartan still: the Minangkabau people of Indonesia forbid crying altogether.
But instead of being ashamed of our tears, we should celebrate them because the human is the only animal that weeps in this way.
Just like speaking, journeying to the Moon and the many other activities that set us apart from other creatures, our tears are special, making us realise what a mysterious and wonderful structure we have in the human head.