Why Don't Penguins' Feet Freeze?: And 114 Other Questions - Mick O'Hare (2009)

Chapter 1. Our bodies

Grey matters

Why does hair turn grey?

Keren Bagon
Radlett, Hertfordshire, UK

Grey (or white) is merely the base ‘colour’ of hair. Pigment cells located at the base of each hair follicle produce the natural dominant colour of our youth. However, as a person grows older and reaches middle age, more and more of these pigment cells die and colour is lost from individual hairs. The result is that a person’s hair gradually begins to show more and more grey.

The whole process may take between 10 and 20 years - rarely does a person’s entire collection of individual hairs (which, depending on hair loss, can number in the hundreds of thousands) go grey overnight. Interestingly, the colour-enhancing cells often speed up pigment production as we age, so hair sometimes darkens temporarily before the pigment cells die.

Bob Barnhurst
Pointe-Claire, Quebec, Canada

Light sneeze

I have noticed that many people tend to sneeze when they go from dark conditions into very bright light. What is the reason for this?

D. Boothroyd
Harpenden, Hertfordshire, UK

Photons get up your nose!

Steve Joseph
Sussex, UK

I think that the answer may be fairly simple: when the sun hits a given area, particularly one shielded or enclosed in glass, there is a marked rise in local temperature. This results in warming of the air and a subsequent upward movement of the air and, with it, many millions of particles of dust and hair fibres. These particles quite literally get up one’s nose within seconds of being elevated, hence the sneezing.

Alan Beswick
Birkenhead, Merseyside, UK

My mother, one of my sisters and I all experience this. I feel the behaviour is genetic and confers an unrecognised evolutionary advantage. I have questioned many people, and we sun-sneezers seem to be in the minority. However, as the ozone thins and more ultraviolet light penetrates the Earth’s atmosphere, it will become increasingly dangerous to allow direct sunlight into the eye. Those of us with the sun-sneeze gene will not be exposed to this, as our eyes automatically close as we sneeze! The rest of the population will gradually go blind, something not usually favoured by natural selection.

Alex Hallatt
Newbury, Berkshire, UK

The tendency to sneeze on exposure to bright light is termed the ‘photic sneeze’. It is a genetic character transmitted from one generation to the next and which affects between 18 and 35 per cent of the population. The sneeze occurs because the protective reflexes of the eyes (in this case on encountering bright light) and nose are closely linked. Likewise, when we sneeze our eyes close and also water. The photic sneeze is well known as a hazard to pilots of combat planes, especially when they turn towards the sun or are exposed to flares from anti-aircraft fire at night.

R. Eccles
Common Cold and Nasal Research Centre
Cardiff, UK

Here are some early thoughts on the subject of light sneezing from Francis Bacon’s Sylva Sylvarum (London: John Haviland for William Lee, 1635): ‘Looking against the Sunne, doth induce Sneezing. The Cause is, not the Heating of the Nosthrils; For then the Holding up of the Nostrills against the Sunne, though one Winke, would doe it; But the Drawing downe of the Moisture of the Braine. For it will make the Eyes run with Water; And the Drawing of Moisture to the Eyes, doth draw it to the Nosthrills, by Motion of Consent; And so followeth Sneezing; As contrariwise, the Tickling of the Nosthrills within, doth draw the Moisture to the Nosthrills, and to the Eyes by Consent; For they also will Water. But yet, it hath been observed, that if one be about to Sneeze, the Rubbing of the Eyes, till they run with Water, will prevent it. Whereof the Cause is, for that the Humour, which was descending to the Nosthrills, is diverted to the Eyes.’

C. W. Hart
Smithsonian Institution
Washington DC, US

Comes in handy

Why do we have fingerprints? What beneficial purpose could they have evolved to serve?

Mary Newsham
London, UK

Fingerprints help us in gripping and handling objects in a variety of conditions. They work on the same principle as the tyres of a car. While smooth surfaces are fine for gripping in a dry environment, they are useless in a wet one. So we have evolved a system of troughs and ridges, to help channel the water away from the fingertips, leaving a dry surface which allows a better grip. The unique pattern is merely a useful phenomenon that is used by the police to identify individuals.

James Curtis
Bradford, West Yorkshire, UK

Fingerprints are the visible parts of rete ridges, where the epidermis of the skin dips down into the dermis, forming an interlocking structure (similar to interlaced fingers). These protect against shearing (sideways) stress, which would otherwise separate the two layers of skin and allow fluid to accumulate in the space (a blister). They appear on skin surfaces which are subject to constant shearing stress, such as fingers, palms, toes and heels. The unique patterns are simply due to the semi-random way in which the ridges and the structures in the dermis grow.

Keith Lawrence
Staines, Middlesex, UK

Crinkle tips

Why does skin - especially of the fingers and toes - become wrinkled after prolonged immersion in water?

Lloyd Unverfirth
Wahroonga, New South Wales, Australia

The tips of fingers and toes are covered by a tough, thick layer of skin which, when soaked for a prolonged period, absorbs water and expands. However, there is no room for this expansion on fingers and toes, so the skin buckles.

Steven Frith
Rushden, Northamptonshire, UK

Your whole body does not become crinkled as the skin has a layer of waterproof keratin on the surface, preventing both water loss and uptake. On the hands and feet, especially at the toes and fingers, this layer of keratin is continually worn away by friction. Water can then penetrate these cells by osmosis and cause them to become turgid.

Robert Harrison
Leeds, West Yorkshire, UK

Take the pils

Why is it that when I walk home from the pub after a few beers, I always stumble to the left more than to the right?

Chris Wood
Liverpool, UK

A similar situation arises when people wander in the forest or desert. Although they may intend to walk in a straight line, if they are lost and have no landmarks to guide them, most people will unconsciously walk slightly towards the left, making a big anticlockwise circle which brings them back to their starting point.

The reason for this is that most people have a slightly stronger and more flexible right leg. This is common knowledge among sports scientists, and most people who have undergone strength tests in their legs can confirm it.

Most people also find they can lift their right leg slightly higher than their left. The right leg has a longer stride than the left one and so when there are no guiding landmarks a circular walking route is the result.

Also, the slightly greater strength of the right leg means that when you push on the ground with your right foot, the push to the left is slightly greater than the push to the right produced by the left foot. The longer stride and greater push combine to cause most people to move in an anticlockwise manner in the course of a long walk.

Han Ying Loke
Edinburgh, UK

The human body is never perfectly symmetrical. In this case, the right leg seems to be longer than the left. A beer mat placed in the left shoe underneath the foot should remedy the problem quite easily.

J. Jamieson
Marlow, Buckinghamshire, UK

Everyone has a dominant eye which they rely on more than the other, weaker eye. Instinctively, we try to walk where we can see best (although we normally correct this to allow us to walk forwards). So when we stumble, it is more likely that we will stumble in the direction of our dominant eye.

This is because the brain, in trying to recover the situation, has to react fast and gives more weight to the information coming from the dominant eye to work out where to put the feet in order to regain balance. Hence the feet tend to be aimed at a position towards the side of your body on which the dominant eye lies, resulting in a stumble in that direction. In this case the questioner’s dominant eye is obviously his left.

This phenomenon can be used to steer riding animals - simply cover up one of their eyes and they will tend to move in the direction of their remaining eye.

Adrian Baugh
Shrewsbury, Shropshire, UK

The questioner obviously walks to the pub with his change in his right pocket and his keys in his left. After spending all his money on beer the weight of his keys pulls him to the left as he walks home.

Simon Thorn
Perth, Tayside, UK

Members of the Department of Physics at Auckland University have held consultations regarding this issue and our most popular theory derives from an application of the simple principles of gravity gathered from our common experience in returning from pubs in Auckland.

Currency in denominations lower than NZ$10 is mostly in coins, some of them quite large in size. During an evening in the pub, the drinker accumulates a large number of such coins in his or her pocket. Assuming that English coinage is similar and that your questioner habitually carries his coins in his left pocket, elementary laws of gravity dictate that his gait will incline to the left. It is not uncommon for some New Zealanders in similar circumstances to actually walk in a circle.

Nelson Christenson
University of Auckland, New Zealand

After standing for endless hours in a pub with your beer glass in your right hand, it is inevitable that you are still subconsciously counterbalancing the glass’s weight, and thus stumbling more to the left. The opposite can be demonstrated in left-handed beer drinkers.

By email, no name or address supplied

By the left

Why is it that when two people walk together they often subconsciously start to walk in a synchronised manner. Is this some natural instinct?

Simon Apperley
Cheltenham, Gloucestershire, UK

The zoologist and specialist in human behaviour, Desmond Morris, says that the reason that people start to walk like each other is that they have a subconscious need to show their companion that they agree with them and so fit in with them. This is also a signal to other people that ‘we are together, we are synchronised’.

Other studies suggest that we adopt the mannerisms of our companions as well, especially our superiors, such as crossing our legs in the same directions as others. An example often given is when, in a meeting, the boss scratches his nose and others at the table then follow him without realising it.

Adithi
Hong Kong

While it is purely unsubstantiated opinion, I do have an answer to why people tend to synchronise their steps. Observing a group of children walking in a park recently, supervised by two adults, I noted that the adults synchronised their steps and direction, while the children walked, ran and skipped apparently at random, running ahead, lagging behind, and deviating from the common course.

Perhaps these children, unpolluted by society’s emphasis on conformity, have not yet learned that it is unacceptable to march to your own drum.

Todd Collins
Wagga Wagga, New South Wales, Australia

The next time you walk alongside somebody, walk out of step. Then try to follow the conversation you are having. You will soon fall back into step, because once you are in step with the other person, it is easier to watch where you are walking and then turn to look at them.

Communication is easier with another person when you are in close proximity and when both faces are relatively stable and not bobbing all over the place.

Hamish
By email, no address supplied

Here is a more prosaic (less sociologically inclined) explanation. When people walk they have a slight side-to-side sway. Two people walking together and out of step would bump shoulders every second step.

Peter Verstappen
Kaleen, ACT, Australia

Helpless laughter

Why is it that if you tickle yourself it doesn’t tickle, but if someone else tickles you, you cannot stand it?

Daniel (aged 7) and Nicolas (aged 9) Takken
Wageningen, The Netherlands

If someone was tickling you and you managed to remain relaxed, it would not affect you at all. Of course, it would be difficult to stay relaxed, because tickling causes tension for most of us, such as feelings of unease due to physical contact, the lack of control and the fear of whether it will tickle or hurt. However, some people are not ticklish - those who for some reason do not get tense.

When you try to tickle yourself you are in complete control of the situation. There is no need to get tense and therefore, no reaction. You will notice the same effect if you close your eyes, breathe calmly and manage to relax the next time someone tickles you.

The laughter is the result of the mild state of panic you are in. This may be inconsistent with ‘survival of the fittest’ theories, because panic makes you more vulnerable. But as in many cases, nature is not necessarily logical.

Sigurd Hermansson
Stockholm, Sweden

Live wire

Where does the force come from when you are thrown horizontally across a room after touching a live electrical connection? I thought there was a reaction to every action, but there is no obvious push from the electricity.

John Davies
Ahmadi, Kuwait

The force comes from your own muscles. When a large electrical current runs through your body, your muscles are stimulated to contract powerfully - often much harder than they can be made to contract voluntarily.

Normally the body sets limits on the proportion of muscle fibres that can voluntarily contract at once. Extreme stress can cause the body to raise these limits, allowing greater exertion at the cost of possible injury. This is the basis of the ‘hysterical strength’ effect that notoriously allows mothers to lift cars if their child is trapped underneath, or allows psychotics the strength to overcome several nursing attendants.

When muscles are stimulated by an electric current, these built-in limits don’t apply, so the contractions can be violent. The electric current typically flows into one arm, through the abdomen, and out of one or both legs, which can cause most of the muscles in the body to contract at once. The results are unpredictable, but given the strength of the leg and back muscles, can often send the victim flying across the room with no voluntary action on their part. Combined with the unexpected shock of an electrocution this feels as if you are being flung, rather than flinging yourself.

The distance people can involuntarily fling themselves can be astonishing. In one case a woman in a wet car park was hit by lightning. When she recovered she found herself some 12 metres from where she was struck. However, in this case there may also have been some physical force involved from a steam explosion, as water on her and the area in which she was standing was flash-boiled by the lightning. She survived, though she was partially disabled by nerve damage and other injuries.

A common side effect of being thrown across the room by an electric shock, apart from bruising and other injuries, is muscle sprain caused by the extreme muscle contractions. This can also damage joint and connective tissue. Physiotherapists, chiropractors and osteopaths might consider asking new patients if they have ever been electrocuted.

Being thrown across the room can save your life by breaking the electrical contact. In other cases, particularly where the source of the current is something they are holding, the victim’s arms and hand muscles may lock on to it. They are unable to let go and, if nothing else intervenes, they may die through heart fibrillation or electrocution.

I recall what may be an apocryphal account of a poorly earthed metal microphone causing a rock singer to be involuntarily locked on to it. Unfortunately, writhing on floor while screaming incoherently was not entirely unusual during his shows, and it was a while before one of his road crew figured out that something was amiss and killed the power.

Roger Dearnaley
Abingdon, Oxfordshire, UK

It is interesting to consider why the subject is thrown across the room rather than freezing in a tetanic posture. It is because some muscle groups dominate others. Compare this with the muscle effects seen in a stroke victim, where, if the stroke is severe enough so that no cerebral control is present over one side of the body, the arm is held flexed (that is wrist bent with fingers pointing to the wrist, elbow bent so that the forearm meets the upper arm) and the leg extended (knee straight, ankle extended so that the toes point to the ground).

This is because without cerebral control, the spinal cord reflexes cause all muscle groups to be active, including both components of any bending and straightening muscle pairs. The dominance of one muscle group over another produces the effect described.

Therefore, if any electrical charge triggers all muscle groups the imbalance in ‘bending and straightening’ muscle pairs produces the force that is required to throw the person across the room.

It’s not at all recommended, but I have heard that if you touch a conductor carrying a current using the back of your hand it is safer than the palm because the resultant muscle spasm does not force you to grip the conductor, producing a continuing electrocution.

There is always the effect on the heart to consider too, but that is another matter.

John Parry
Cowling, North Yorkshire, UK

Left in doubt

As a left-handed person I was both amused and annoyed by an article in New Scientist which suggested that left-handed people are at greater risk of accidental death. How can this be? Surely a right-handed person has just as much chance of dying accidentally as I do. Or is there some unknown factor involved?

Alan Parker
London, UK

Approaching obstacles, right-handed people will, in general, circumvent them by going to the right, while left-handed people will go to the left. If two same-handed people approach an obstacle from the opposite direction they will walk safely around it without bumping into one another en route. If two people of different handedness approach an obstacle from the opposite direction, they will pass on the same side leading, potentially, to a bump. Because most people are right-handed, it is left-handed people that most frequently find themselves bumped in these situations. This is a simple example, but taken to extreme and multiplied by a lifetime of bumps, the result is a shorter life expectancy for left-handed people.

Hannah Ben-Zvi
New York, US

We left-handers are at greater risk of accidental death because industrial tools and machinery are designed for the right-handed. Left-handers are, therefore, more likely to chop off parts of themselves in all manner of mechanical devices. An interesting example is the SA-80 assault rifle. When fired from the left shoulder, it ejects spent cartridges, at great velocity, into the user’s right eye.

Daniel Bristow
Kew, Surrey, UK

No flakes

How does antidandruff shampoo work?

Eugene
By email, no address supplied

Dandruff is thought to be caused by overgrowth of yeasts such as Pityrosporum ovale which live on normal skin. This overgrowth causes local irritation resulting in hyperproliferation of the cells (keratinocytes) which form the outer layer of the skin. These form scales which accumulate and are shed as dandruff flakes.

Antidandruff shampoos work by three mechanisms. Ingredients such as coal tar are antikeratostatic and they inhibit keratinocyte cell division. Detergents in the shampoo are keratolytic - they break up accumulation of scale. Finally, antifungal agents such as ketoconazole inhibit growth of the yeast itself. Other components such as selenium sulphide also inhibit yeast growth and therefore scaling.

Roddie McKenzie
University of Edinburgh, UK

Gas gassing

Why does speaking through helium raise the frequency of the sounds emitted, even when the final transmission to the hearer is through air?

David Bolton
Mosgiel, New Zealand

Sound travels faster in helium than in air because helium atoms (atomic mass 4) are lighter than nitrogen and oxygen molecules (molecular mass 14 and 16 respectively). In the voice, as in all wind instruments, the sound is produced as a standing wave in a column of gas, normally air. A sound wave’s frequency multiplied by its wavelength is equal to the speed of sound. The wavelength is fixed by the shape of the mouth, nose and throat so, if the speed of sound increases, the frequency must do the same. Once sound leaves the mouth its frequency is fixed, so the sound arrives to you at the same pitch as it left the speaker. Imagine a rollercoaster ride. The car speeds up and slows down as it goes around the track, but all cars follow exactly the same pattern. If one sets out every 30 seconds, they will reach the end at the same rate, whatever happens in between.

In stringed instruments, the pitch depends on the length, thickness and tension of the string, so the instrument is unaffected by the composition of the air. Releasing helium in the middle of an orchestra would therefore create havoc. The wind and brass would rise in pitch, while the pitch of the strings and percussion would remain more or less the same. In the Song of the White Horse by David Bedford, the lead soprano is required to breathe in helium to reach the extremely high top note.

Eoin McAuley
Dublin, Ireland

Brain waves

Why are there fissures or folds in the surface of the brain?

Brian Lassen
Canberra, Australia

The brain has fissures to increase the surface area for the cortex. Dimmer animals such as rats have smooth brains. Much of the work carried out in the brain is performed by the top few layers of cells - a lot of the brain’s volume is, in effect, point-to-point wiring.

So, if you need to do lots of processing, it is much more efficient to grow fissures than it is to expand the surface area of the brain by increasing the skull diameter.

Anthony Staines
By email, no address supplied

Evidently they are there to maximise the surface area of the brain cortex. The real question is why this is necessary. The answer probably lies in the relative number of short-range and long-range connections needed.

If many short-range connections are required, it makes more sense to pack the processing units into thin, almost two-dimensional, plates and reserve a third dimension for long-range connections.

If the neurons were distributed homogeneously over the whole volume of the brain, long-range connections would possibly be shorter, but they would take up the space between the computational units of the brain and thus lengthen the short-range connections, increasing the overall brain volume.

Janne Sinkkonen
Finland

Another possible answer lies in the amount of heat produced in the brain - Ed.

Brain tissues consume massive amounts of energy and the resulting heat that is generated has to be dumped. Put your hand on your head and feel how hot it feels compared to your thigh.

Brains of lower vertebrate animals lack extensive folds because they have relatively less heat to get rid of.

Humans, on the other hand, have large brains which do a lot of work. The extra folds in our brains increase the surface area for blood vessels to dump the excess heat produced by all that hard thinking. If our brains were to evolve into more complex and larger organs, their folding would have to increase exponentially in order to be able to release the additional heat that they would produce.

Gerald Legg
Brighton, West Sussex, UK

Many intelligent vertebrates are endowed with both large brains and a very convoluted cerebral cortex. Therefore, although the dolphin and the shark are of similar size, the dolphin’s brain is considerably larger and more convoluted than that of the shark.

The cat and the rabbit are also of similar size to each other but the cat, being carnivorous, has a more complex lifestyle, presumably necessitating greater intelligence, so the cat has a convoluted brain while the rabbit does not.

The size of the animal is also an important factor. Mice and rats, while showing intelligent behaviour, have hardly any fissures in their brains but elephants and whales have brains that are even more convoluted than a human’s.

It is interesting that this larger amount of cerebral cortex does not necessarily correspond to a larger number of cortical nerve cells. It turns out that these are larger and more widely spaced in large animals.

One reason for this is that the ratio of glia to neurons is considerably greater in these large vertebrates. As a result, the cerebral cortex - a laminar structure - needs to become folded to contain the number of neurons that smaller animals can afford to have in a non-folded cortex.

E. Ramon Moliner
North Hatley, Quebec, Canada

Concentration

People doing a tricky job will stick their tongue out and clamp it between their lips. Why? Does this happen in all cultures?

Steve Townsend
No address supplied

When you need to concentrate on something, say a word problem, you are using the hemisphere of the brain also used for processing motor input. It is amusing to see people slow down when they are thinking of something difficult while walking. This is caused by interference from the two activities fighting for the same bit of brain to process them. I suppose by biting your lip or sticking your tongue out, you are suspending motor activity and also keeping your head rigid, to minimise movement, and hence interference.

Melanie Western
By email, no address supplied

Large areas of the brain are devoted to control of the tongue and to the receipt of sensation from it.

Perhaps with the tongue held rigid against the teeth or lips, the activity of those areas is subdued, allowing delicate tasks like threading a needle to proceed with less interference.

Barry Lord
Rochdale, Lancashire, UK

What’s the crack?

What causes the noise when you crack your knuckles or any other joint?

Marty Brown
By email, no address supplied

A click or crack is often heard when a joint is moved or stretched. When the pressure of the synovial fluid in the joint cavity is reduced, this may create a gas bubble and generate a popping sound. The sound may also be the result of separating the joint’s surfaces, which releases the vacuum seal of the joint.

These noises are sometimes produced during osteopathic treatment, but this does not prove that the treatment has worked, nor does their absence mean the treatment has failed. The test of success is whether the joint’s range and ease of movement have been improved.

Will Podmore
The British School of Osteopathy
London, UK

All the soft tissues of the body, including the capsules of joints, contain dissolved nitrogen. When a vacuum is applied to the joint space by pulling on the bones, say by flexing the fingers strongly, nitrogen suddenly comes out of solution and enters the joint space with a slight popping sound.

Radiologists often see a small crescent of gas between the cartilages of the shoulder joint on the chest X-rays of children who are held by the arms. This is due to the force of pulling on the arms causing nitrogen to evaporate into the joint space. It can infrequently be seen in the hip too.

Small, highly mobile bubbles sometimes appear within the hip joint of a baby being screened for congenital dislocation of the hip using ultrasound. This usually happens if the infant is struggling and has to be held firmly. The bubbles disappear after a short while when the nitrogen dissolves again.

If the fingers were X-rayed immediately after cracking the knuckles a fine lucency, as a result of thousands of tiny opaque bubbles, would probably be visible between the ends of the bones.

Tony Lamont
Mater Children’s Hospital
Brisbane, Queensland, Australia

Wine into water

No matter what colour of drink one consumes, when the liquid finally leaves the body the colour has gone. What happens to it?

P. Beeham
Witney, Oxfordshire, UK

The liquid that leaves the body is almost unrelated, in chemical composition, to the liquid consumed. Any substance, solid or liquid, that goes down the oesophagus, passes through the digestive tract and, if not absorbed, is incorporated into the faecal matter. Urine, in contrast, is created by the kidneys from metabolic waste produced in the tissues and transported through the bloodstream.

Any coloured compound that you drink either will or will not interact biochemically with the body’s systems. If it does, this interaction (like any other chemical reaction it might undergo) will tend to alter or eliminate its colour. If it does not, the digestive system will usually decline to absorb it and it will be excreted in the faeces which, you will have noticed, show considerably more colour variation than the urine.

Stephen Gisselbrecht
Boston, Massachusetts, US

Coloured substances in food and drink are usually organic compounds that the human body has an amazing ability to metabolise, turning them into colourless carbon dioxide, water and urea. The toughest stuff is often taken care of by the liver, which is a veritable waste incinerator. However, on the very infrequent occasion when the intake of coloured substances exceeds what the body can quickly metabolise, the colour is not necessarily removed as the liquid leaves the body. This is well known to anyone who has indulged in large quantities of borsch (Russian beetroot soup).

Hans Starnberg
Gothenberg, Sweden

Grave concern

A friend’s grandfather was exhumed a little while ago in southern Italy in order to be reburied next to his recently deceased wife. Amazingly, his body was found to be completely intact and no decomposition at all seemed to have taken place. Yet he died about 30 years ago from his injuries in a serious car accident, and had been buried in an ordinary coffin. Is this a common occurrence? How can a body not decompose in this time? Is soil or geographyimportant?

Kira Kay
Rosebank, New South Wales, Australia

Non-decay of a dead body is more common than most people suppose. Many saints have had their claim to sainthood upheld by the nifty trick of not going off after burial. More mortal examples include the wife of Dante Gabriel Rossetti, who troubled him somewhat by being revealed in all her undecayed glory when, short of a few quid and lacking fresh inspiration, he broke into her grave to steal back the poems he buried with her.

This type of preservation happens when the adipose tissue in the body forms adipocere, a soapy-textured substance, composed mainly of saturated fatty acids and salts of fatty acids. The colloquial term for an adipocere-ridden corpse is a ‘soap mummy’.

Women tend to be preserved more often than men, probably because they have more fat to start with, and conditions such as humidity and warmth also have an effect. The dead person in the question, having been buried in southern Italy, probably had a better chance of preservation than he would have had he been stuck in the cold mud of England; some very well-preserved adipocere corpses have been discovered in Italy.

Adipocere can either form quickly, within weeks, or after several years. In the latter case a body may reach quite an advanced stage of decay before the development of adipocere sets in. It helps if a body is overweight, as an obese corpse contains enough water and fat to start adipocere formation quickly, regardless of the burial conditions. It can also be encouraged by covering the body in clothing or a shroud made of artificial fibres, by moist conditions, and by the presence of a substance such as formaldehyde. In rare cases, not only fat but also muscle turns to adipocere. If the body was in very good condition, this might have been the case.

Anne Rooney
Cambridge, UK

For a body to putrefy in a grave there needs to be enough moisture to allow tissue breakdown both from autolysis and from the action of micro-organisms, usually starting in the ileocaecal region of the intestine. In arid conditions, including dry soil, the corpse will lose water, principally by evaporation as the drier material around it draws the water away. This could even occur through the walls of a wooden coffin, provided the surrounding soil was dry enough to continue absorbing water and conditions were warm enough to encourage evaporation.

The location of the grave in southern Italy suggests that these conditions were present, and this is probably what stopped putrefaction. Indeed, bodies left above ground can be partially preserved by this process - for example, in haylofts, where the surrounding dry hay and air draw water out of the dead body.

An extension of this process is found in natural graves in arid regions that have correspondingly dry soil, to the point at which nearly all the water is removed to leave dry, leathery tissues. This is mummification, and its natural occurrence in the dry sands of Ancient Egypt probably encouraged mummification there as a cultural practice.

Alan Taman
Sutton Coldfield, West Midlands, UK

That’s life

What chemical formula would accurately describe an adult human being, in terms of the relative distribution of elements (including pollutants)? And what might be the formula for the first alien life form we encounter?

Paul Montmorency
London, UK

One’s ‘chemical formula’ depends on a number of factors, most notably whether we’re talking about a he or a she. Male bodies contain more water than female bodies, which have extra lipids. By weight, oxygen amounts to about two-thirds of the body, followed by carbon at 20 per cent, hydrogen at 10 per cent and nitrogen at 3 per cent. Elements originating from pollutants would only be present in trace amounts.

If a human body were broken into single atoms, we would arrive at an empirical formula H₁₅₇₅₀ N₃₁₀ O₆₅₀₀ C₂₂₅₀ Ca₆₃ P₄₈ K₁₅ S₁₅ Na₁₀ Cl₆ Mg₃ Fe₁. The relative numbers of atoms in this differ from the composition by weight because atoms have different masses.

The composition of an alien life form would depend on two key factors. First, the element that forms the ‘skeleton’ of its macromolecules. All life discovered so far is based on carbon, which can form long chains to which other elements bind. The most likely alternative building blocks for macromolecules would be silicon, phosphorus or nitrogen. Second, the solvent for the biochemical reactions that drive the body. The most likely alternative to water is probably ammonia (NH₃) because it can dissolve most organic molecules. It is also liquid well below water’s freezing point and is prevalent in space. So an alien life form might be silica and ammonia based.

Lauri Suoranta
Espoo, Finland

The chemical elements in an adult human are distributed in various molecular and atomic species. An accurate formula could be expressed in the standard form: 7x10²⁵H₂O+9x10²⁴ C₆H₁₂O₆+2x10²⁴CH₃(CH₂)₁₄+ … and so on. However, such a series would fill a book and we cannot possibly identify all species. Metabolism, defined as the chemical and energy exchanges in a living body, means that any such chemical formula is continually changing.

Having a chemical formula for a process can be useful. If we find all the elements and determine all the mathematical expressions applying to them, the whole process can be determined. But this is not the whole story. Life is characterised by extensive, adaptive self-regulation of its own structural order, and utilises feedback control. An organism uses its resources in its own emergent way. The chemical reactions work, but how they are brought together is a matter of emergent control systems. This means that not only is it impossible to write an accurate formula for a human being, it is unnecessary and can be misleading to try. Life is what it does with chemical species, not just which ones it is made from.

I guess the same would go for any alien life form we might encounter. We spend considerable time searching the electromagnetic spectrum to detect their signals, and we receive a lot of signals. But how will we know if any of them are life? Only, I suppose, if they show the characteristic of life: I’m in control, and I’m not solely a bottom-up deterministic chemical process.

John Walter Haworth
Exeter, Devon, UK

Zzzzapppp

When people die of electric shocks, what kills them - current or voltage?

Kyle Skotzke
Brookfield, Wisconsin, US

It is the current through the heart region that causes most deaths from electric shock. The effect depends on duration of exposure and also varies between individuals. The frequency of mains power - around 50 or 60 hertz - is very dangerous, and currents of only a few tens of milliamps at such a frequency can cause the heart to fibrillate. It pulses at a much higher rate than normal and fails to pump blood to the brain; death follows in a few minutes.

Because the body has electrical resistance, the current flowing in it depends on the voltage. It also depends on the dampness of the skin and where on the body the current enters and leaves. It is therefore very difficult to come up with a safe voltage for all circumstances. This is being attempted at the moment by the International Electrotechnical Committee (IEC) working group on electric shock, but the number of variables makes simple recommendations difficult.

There are other mechanisms that can cause death from electric shock. One of these is muscular contraction. If a current passes through the chest it can inhibit breathing and lead to asphyxia. A current in the head can affect the respiratory centre in the brain, again leading to asphyxia. Once more it is current, rather than voltage, that is the critical factor.

Most people who receive an electric shock survive. This is not because they are particularly strong but because there is usually some factor that reduces the current, such as resistance from clothing or shoes, or the length of the shock. An earth-leakage circuit breaker (also called a residual current device or ground-fault circuit interrupter), often touted as a panacea, is useful to shorten the duration of a shock but does not prevent the shock occurring in the first place.

In short, it is a function of current and time that kills.

N. C. Friswell
International Electrotechnical Committee working group on electric shock
Horsham, West Sussex, UK

Damage from an electric shock varies with current. However, except in the case of superconductors, voltage is needed to drive this current so the distinction is a little artificial. If the resistance of the human body were constant then voltage would be an equally valid yardstick. But the resistance varies according to a number of factors.

For example, dry skin offers an electrical resistance of 500,000 ohms. Yet wet skin reduces this to 1000 ohms - only double the resistance of salty water. So being soaked to the skin leaves us more vulnerable to harm.

The path of the current is critical. This is why standing on insulating material and doing electrical work with one hand behind your back, so that an earthed current will not pass across your chest but down to your feet, reduces the chance that a current will pass through your heart. The heart can stop if current passes through it, and we can suffer severe burns as electrical energy is converted to heat.

Alternating current is said to be four or five times as dangerous as direct current, because it induces more severe muscular contractions. It also stimulates sweating, which lowers the skin’s resistance, increasing the current passing through the person. Sixty cycles a second happens to be the most harmful range.

Thomas Edison tried to take advantage of this fact when, in 1886, New York state established a committee to replace hanging with a more humane form of execution. He employed Harold Brown to invent the electric chair, powered by the alternating current that was favoured by his rivals in the race to commercialise electricity distribution. If it were used to kill criminals, Edison hoped that potential customers would shun alternating current in favour of the direct-current system he had developed. Sadly for Edison, this interesting piece of marketing turned out to be unsuccessful because AC proved to be cheaper and can be stepped up to higher voltages to be transported more efficiently over great distances.

Mike Follows
Willenhall, West Midlands, UK

Electricity kills by delivering energy where it is not wanted. Energy is the product of voltage, current and time. It could be lethal when delivered as low as 100 microamps at a few volts if sent directly to the heart, or about 30 milliamps at a few hundred volts from one hand to another. In both cases the problem arises if the shock disorganises the electrical activity of the heart to make the ventricles fibrillate. Of course, the solution to this problem is to deliver another shock, from a defibrillator, if you have one handy.

Electrical energy can kill you in other ways. The electric chair appears to kill by asphyxiation, because it causes uncontrolled contraction of the muscles of respiration. It also cooks its victims a bit, but does not seem to reliably produce either ventricular fibrillation or rapid loss of consciousness from current through the brain. In other circumstances, large currents that pass through the body without causing instant death can cause horrible, deep burns. These can, of course, kill you more slowly. Finally, a high-voltage discharge can set fire to your clothes or blow you off the electricity pylon you might be working on, either of which can be fatal.

Mike Brown
Knutsford, Cheshire, UK

Take your pick

Is it coincidence a human finger fits exactly into a human nostril?

If not, why does my mum tell me not to do it?

Jack Walton (aged 9)
London, UK

Your mother may not approve, but there is a way to clear your nose without sticking anything inside it. It’s called the ‘snot rocket’. Just push against the side of one nostril to close it off, take a deep breath, close your mouth and exhale as hard and sharply as you can through your other nostril. You’ll be amazed how fast the contents shoot out. Just make sure you tilt your head away from your body to avoid peppering yourself.

Nose-clearing tactics like the snot rocket mean there is no life-or-death reason for the co-evolution of digging digits and large, inviting nostrils. After all, nose blockage is easily managed by breathing through your mouth. In fact, a blocked nose is really only a problem if something gets lodged near your nasal bones, where it is dangerously close to your brain. That is a region where human fingers are too podgy to be of any use. A rather thrilling story of a primatologist, some tweezers and an engorged Ugandan tick comes to mind.

Sexual selection might have favoured the relationship of finger to nostril if, say, females in the Pleistocene preferred mating with males who picked their noses, or if males and females picked each other’s noses in a courtship ritual. However, that would be taking reciprocal grooming a little far.

So we must conclude that, yes, it is mere coincidence that your fingers fit so nicely into your nostrils. I doubt the made-for-each-other argument is going to change your mum’s opinion of rhinotillexomania. I suggest you demonstrate the snot rocket instead and see what she says.

Holly Dunsworth
State College, Pennsylvania, US

Organs commonly correspond in size and shape to other organs with which they must function. Conspicuous examples include the male and female sexual organs of many insects and some mammals, the mouths of baby marsupials and their mothers’ nipples, and - in many animals - elongated claws or toes that have been adapted for grooming. However, a mismatch need not mean that the organs cannot work together. For example, the mammalian female birth channel can obviously accommodate the passage of young that are far bigger than the male sexual organ. Apertures often expand or shrink to fit the organs that they match.

Conversely, it does not follow that, because an organ fits an aperture, it is other than coincidental. There are some other places your finger would fit into that your mum would tell you firmly to leave alone, especially if you were in public.

You have five sizes of finger and two nostrils, so to get some sort of fit does not demand much of a coincidence. Nor is there any obvious reason why there should be any selective pressure to adapt nostrils to finger-reaming. More likely, nature intended us to dribble snot just as elephant seals do. The fine art of nose-picking is just another adventitious one in the eye for intelligent design.

Jon Richfield
Somerset West, South Africa

While I agree that an expertly executed unilateral snot-rocket is indeed a thing of beauty and wonder, I would caution against Holly Dunsworth’s suggestion that you ‘exhale as hard and sharply as you can’ from one nostril. My developing expertise in this technique as a schoolboy was brought to an abrupt halt by a burst sinus and severe nosebleed.

Duncan Hannant
Professor of Large Animal Immunology
University of Nottingham
Loughborough, Leicestershire, UK

I’d also like to add a word of warning that this method isn’t particularly hygienic, and could spread any number of diseases. Snot rockets should really only be practised when you are by yourself.

Bron
Australia