The Miracle that is a Human being

 

Human being 

Humans are amazingly complex living creatures - the product of millions of years of evolution. Our most conspicuous external characteristics are that we walk in an upright position and lack body hair. However, it is the large human brain and its achievements that make us unique among the other creatures that share the planet with us. As far as we know, no other animal can develop theories and think about them, or translate thoughts into language and then record them for posterity as we do.

Do we have senses for everything ?

Our five senses enable us to receive vital information from our environment. However, they deliver only a tiny part of all that is available out there. We can't see either ultraviolet or infrared light and our ears are deaf to ultra- and infrasound. Many animals can smell, taste and feel things far better than we can and, unlike some animals, we have no sense organ that enables us to detect magnetic fields.

What is the connection between taste and smell ?

The nose has more to do with the flavours we experience when we eat and drink than the tongue. We are only able to experience the full flavour of a food or drink with the help of olfactory cells in the mucous membrane of the nose. You can confirm this by simply holding your nose as you eat. There are sensory cells in the mouth, throat and especially on the tongue, but these only react to a few taste sensations, including sweet, sour, salt and bitter.

As we eat or drink, molecules reach the olfactory cells in the mucous membrane of the upper nasal cavity. These olfactory cells are extremely sensitive and can distinguish between hundreds and even thousands of different aromas. The brain combines the flavour and olfactory signals that are received separately to create a single taste sensation.

Why do hot spices burn the mouth ?

The hot, spicy taste of foods is not, in fact, a taste sensation but a feeling of pain. Capsaicin - the chemical compound that makes chilli peppers hot - binds to proteins, or pain receptors, of nerve cells in the mucous membranes of the nose and mouth. The nerve impulses produced in this way pass via the trigeminal nerve into the brain, creating a painful burning feeling. The same receptors also react to heat, so that when heavily spiced food is eaten hot, the effect is even more intense. However, the pain is offset by the body's reaction, which is to release endorphins - naturally occurring opioids that produce a feeling of wellbeing - which could explain the popularity of hot, spicy food. Another positive effect of hot spices is that they kill pathogens and promote sweating - the latter effect being especially useful for cooling the body in hot climates.

How is a fresh, minty taste created ? 

The fresh taste and smell of peppermint oil is due to the menthol it contains. However, olfactory and taste cells in the nose and mouth play no part in this sensation. Rather, menthol stimulates the nerve cells in the mucous membranes which normally react to cold. The trigeminal nerve carries the impulses produced by this reaction to the brain, where the impression of cooling freshness is linked to other taste and smell signals.

Can we imagine pain ?

These were explained as symptoms of psychological disorders. However, we now know that chronic pain can lead to changes in the central nervous system. Sufferers develop a sort of pain memory, so that they continue to feel pain, even when the original trigger has long since disappeared. This helps to explain why some people develop hypersensitive reactions to harmless minor irritations.

The phantom pain that some people claim to feel in a part of the body that has been amputated may be the result of a region of the brain recalling earlier pain signals. In the absence of these earlier signals, other signals produce the same feelings of pain. Medication or electrical stimulation can help the brain to forget previously experienced pains.

Are men or women more sensitive to pain ?

Not only do women experience pain more frequently than men, they are actually more sensitive to it. Why this is so has not yet been fully explained, but it is a fact that women have greater sensitivity to touch, which could be due to differences in their skin structure. Research has found that the facial skin of a woman contains twice as many pain receptors as that of a man.

One thing that is clear, however, is that male and female sex hormones play a major role in how each gender experiences pain. Women, for example, experience pain differently at various stages during their menstrual cycle. In the late stages of pregnancy, hormones cause the body to release increased numbers of pain-relieving neurotransmitters to make the pain of giving birth more bearable. As oestrogen levels fall after the menopause, sensitivity to pain also decreases. In males, the sex hormone testosterone has a clear influence on pain, with experiments showing that raised levels reduce pain.

Why are many physical reactions involuntary ?

Vital bodily functions like breathing, heartbeat, digestion and temperature control are regulated unconsciously. They are governed by what is known as the autonomic nervous system. Since these processes have to be kept going non-stop, waking or sleeping, it would not make sense for them to be controlled voluntarily. It is only because they are fully automatic that important reflexes occur quickly and reliably.

Why do we sweat ?

The human body has between 2 and 3 million sweat glands distributed over its surface. Their job is to release fluid when the body becomes overheated. Sweat is made up of salt, protein and urea dissolved in water. As it evaporates on the skin, it produces a cooling effect which helps to reduce body temperature. Extreme heat or physical effort produces more than 1 litre of sweat per hour.  

Hot and spicy food can also cause us to sweat, as can fear and stress when messages pass to the autonomic nervous system which controls perspiration. Damp, sweaty hands, that can grasp things better than dry ones, are a part of our natural fight-or-flight response. How heavily an individual perspires is genetically determined, but there are also gender differences to take into account. Some disorders can cause excessive sweating, with up to five times as much sweat being produced as normal.

Are swimming and walking innate skills ?

Newborn and very young babies possess a number of reflexes, some of which they lose very quickly. These include the stepping, swimming and breath control reflexes. When a baby is plunged into water it reacts by closing its mouth and windpipe while making swimming movements. These automatic reactions disappear at the age of three to four months, and children can really only learn to swim when they are three or four years old.

The automatic stepping movements, which babies make when held upright with feet touching a flat surface, are also lost after three months. Only much later are the leg muscles and sense of balance sufficiently developed to enable the child to stand upright and walk. Other .babyhood reflexes, such as swallowing, coughing and sneezing, are retained permanently.

Why do we sleep ?

We know for certain that a person must sleep to stay physically and mentally fit. What we do not know is why. One important reason is presumably that sleep helps the body to recover, since heartbeat, breathing and many organs work more slowly during sleep than they do when we are awake. By contrast, the brain is highly active during sleep. It uses the time to assimilate experiences, to consolidate what has been learnt the previous day, and even, perhaps, to erase useless information.

Our internal clock regulates how tired we get and how long we sleep, causing the brain to release neurotransmitters which induce sleep. These include the sleep hormone melatonin, which the pineal gland produces in larger quantities during the hours of darkness. The need for sleep is determined by our genes, and varies considerably from one person to another. Anything between four and 12 hours a day is considered normal, provided a person feels well.

Why is blood red ?

Red blood cells contain the protein haemoglobin, which gives it its red colour. To be more precise, the haem group of protein molecules - or even more precisely the iron attached to them - is responsible for the colour.

Haemoglobin's task is to bind with the oxygen in the lungs, transport it to the rest of the body and then release it. To do this, the haem group enters into a loose chemical bond with oxygen, which is easily released in surroundings where oxygen is in short supply. Haemoglobin is bright red when full of oxygen. Without oxygen, the molecular structure changes and with it the absorption of light that dictates its colour. This is why blood that is deficient in oxygen appears darker.

What does healthy really mean ?

Sixty years ago, the World Health Organization defined health as 'a state of complete physical, mental and social wellbeing'. By this measure, most people could be said to be unhealthy for most of their lives - even in industrialised countries. Today, health is regarded more as a subjective awareness of wellbeing. Of course, the prerequisites for wellbeing are still sufficient amounts of healthy food and physical activity and adequate amounts of sleep, as well as a healthy environment and good social relationships.

What is the maximum age for humans ?

The maximum human lifespan is around 125 years. However, some experts believe that this limit could be extended by somewhere between 10 and 15 years. So far, the oldest person whose age could be proved was a Frenchwoman who died in 1997 at 122 years of age. In 1933, The New York Times reported the death of a Chinese man who was allegedly 253 years old, but this and similar reports of people living to such great ages are now considered unreliable. Over the course of history, there has been no change in the maximum age, which is the same for all ethnic groups. What has increased since the end of the 19th century is the average life expectancy in industrialised countries. Thanks to the improvement in living conditions, this is now between about 79 and 82 years for both sexes (at birth).

Why is it that women live longer than men ?

On average, women live seven years longer than men, although in some parts of the developing world the gap is not as wide. Men of all ages in industrialised countries run a greater risk of dying than women. This is particularly true of young men and those over 60. At first, it was thought that this difference had biological origins and might, for example, be due to sex hormones. However, a study carried out in German monasteries and convents found that monks lived almost as long as nuns and other women. It seems clear that lifestyle and living conditions play a greater role in life.

What causes Cancer ?

The causes of cancer vary enormously, but all cancers result from damage to the genes that control cell growth. Large numbers of these genes control the distribution, development and ageing of body cells.

Scientists have known for a long time that ultraviolet rays from the sun can damage the DNA of sunbathers. The carcinogenic (cancer-causing) effects of certain chemicals, such as those present in tobacco smoke, have also been recognised for many years. Infection by viruses, such as those that cause warts and hepatitis, can also encourage some forms of cancer. When genes become damaged, cells can grow far beyond their usual limits and can become cancerous.

However, even without external influences, faults in the replication of DNA, or random mutations, at any stage in an individual's life can increase genetic susceptibility to cancer. It is usually very hard or impossible to determine afterwards what exactly it was that triggered the disease in the first place.

According to a recent theory, tumours develop after genetic damage to the stem cells found in all body tissue. This theory suggests that therapy can only be really successful if treatment can completely destroy these cancerous stem cells.

How does our brain shape our personality ?

The brain processes and stores everything that is important for our lives - from our most basic instincts and reflexes to our personal memories and the skills and abilities we have inherited or learned. It is this that makes us who we are.

When can a person called intelligent ?

What makes human intelligence so special is our ability to use insight and thought to tackle new tasks and to find our way around in new situations. Depending on the extent to which this ability is greater or lesser than average, we talk about different levels of intelligence. An intelligence quotient, or IQ, of between 90 and 110 is regarded as normal. An IQ of between 70 and 90 indicates learning difficulties, while a score below that level points to mental disability. However, within the overall range of intellectual impairment, even an IQ of between 50 and 70 is still classified as mild. Only when a person's IQ is less than 50 does independent living become virtually impossible. At the other end of the scale, people with an IQ of more than 110 are classified as very intelligent, while those who score 130 or above are regarded as gifted.

Does intelligence changes as we grow older ?

The term intelligence does not always mean the same thing. As early as the 1950s, scientists distinguished between fluid and crystallised intelligence. Fluid intelligence is the ability to find ways of dealing with a new situation and to quickly grasp its implications, even in the face of distraction or disturbance. Crystallised intelligence, on the other hand, is the end product of accumulated learning. Both forms of intelligence change in different ways over the years. As people get older, their ability to react quickly to new situations may decline, but their fund of knowledge has grown steadily larger over the years.

Is it possible to become more intelligent ?

From what we know today, it is not possible to increase intelligence, either with the use of some kind of brain machine or by taking special dietary supplements. Nevertheless, it is possible to compensate for low intelligence by exercising the brain and acquiring knowledge and experience. That is why it is important to stimulate less intelligent children those with Down syndrome, for example - as much as possible. Of course, people of average intelligence can perform better than those with above-average brainpower in particular areas where their accumulated knowledge-in other words, their crystallised intelligence - is superior. Chess is regarded as the greatest of all strategic games, and studies have shown that highly intelligent beginners don't fare so well when matched against less intelligent experts who have been playing for a long time.

Why can't we remember being born ?

How far back each of us can remember varies from person to person, but authentic and conscious memories of events that occurred before the age of one are thought to be unlikely. It is even less likely that anyone can truly remember being born. The scientific explanation is that too few brain structures are fully developed at the time of birth. Moreover, memory seems to be firmly linked to language acquisition. Experiments have shown that people are only able to remember experiences that they were able to describe in words at the time the incident or event took place.

Where is memory located in the brain ?

Memory is not a single, simple ability or process. Experts know this from their observations of Alzheimer's disease and people with memory loss. Dementia patients may not remember what they did five minutes ago, but they can often remember details like their place of birth or childhood songs. People with amnesia can often identify pictures of well-known personalities or famous figures from history - but fail to recognise members of their own family. This is why researchers now believe that there are several different types of memory. Procedural memory stores knowledge, such as how to tie a shoelace or ride a bicycle. Episodic memory records experiences, while declarative or semantic memory retains facts.

The contents of our declarative memory is stored in the neocortex of the brain, and those of episodic memory in the frontal and temporal lobes. Procedural memory, on the other hand, is so various that it has to be stored in different locations throughout the brain, including the motor cortex, basal ganglia and cere bellum. Another part of the brain - the hippocampus plays a major role in transferring the contents of short-term memory into long-term memory.

Does the brain need sleep ?

Research has consistently shown that sleep and brain function are closely connected. Sleep is not only important in consolidating what has been learnt, it apparently also ensures that new brain structures are formed in babies and small children, which in turn promotes further learning. It is obviously not possible to conduct sleep deprivation experiments on babies, so conclusions must be drawn from experiments with very young cats. A number of kittens were presented with new stimuli. Some were allowed to sleep for six hours afterwards, while the others were kept awake and provided with further stimuli. The brains of the kittens that had been allowed to sleep exhibited more changes than those of the ones that had been kept awake.

How did our brain evolve ?

With a history dating back about 500 million years, the oldest part of the brain is the brain stem. It is also known as the reptilian brain because even our distant ancestors had one. It is responsible for the body's basic functions, including movement, is very slow to learn and is completely devoid of emotion.

Above it is the midbrain, which acts as a kind of control centre for breathing and a variety of other reflexes. It is also connected to the cerebellum, which is responsible for physical coordination and balance. These parts of the brain have a 250-million-year history.

The youngest part of the brain is the cerebrum, with the cerebral cortex. It is thought to have first appeared only 200 million years ago. The cerebrum is the seat of consciousness, where memories are stored, and where thoughts, wishes, intentions and ideas are formed.

Are men's brain different from women's ?

On average, men have larger brains than women, although this does not mean that they are in any way intellectually superior, something on which scientists now largely agree. Men often have more nerve cells in the cerebral cortex than women, although the cells in the female cerebral cortex are better connected. The corpus callosum-the structure that connects the two halves of the brain- may be wider in women. Although there are broad general differences, we should not forget that every brain is individual and unique.

The real meaning of dreams..

Dreams are amongst our most mysterious experiences. They can be strange, funny, frightening or stimulating - but as a general rule, they immediately fade from memory when we wake.

Which dreams do we remember most clearly ?

We usually only remember the fact that we have had intense dreams when we wake. This makes sense, since we usually have several dreams each night. If we do remember a dream, it is likely to have occurred in the last stage of dreaming prior to waking, but for some people, its contents tend to fade as soon as we try to recollect it. Only nightmares, or dreams of a particularly emotional nature, stick in our memories.

Are humans 'wired' for language ?

Humans certainly seem to be programmed for language learning, and it is a fact that they will only fail to speak if actively prevented from doing so. Evidence of the extent to which language is a human characteristic seems to be supported by the observation that even people with serious mental disabilities - who are unable to learn to read and write- can and do learn to speak a language.

What factors have an effect on our emotions ?

Much of what affects our emotions is already pre-programmed by the way our brain is designed, and quite a lot is genetically determined. However, there is also a great deal that is learnt, and sometimes our emotions can even be shaped by historical developments.

Can we believe in love at first sight ?

Love at first sight is not, in fact, just some cliché from the world of romantic novels and films - it really does happen. Experiments conducted by behavioural scientists have even shown that the so-called first sight has to last for around 30 seconds, but not much longer than that. The critical 30 seconds is long enough for us to decide whether we are interested in the person in question or not. It is enough time for a fairly long period of eye contact, or for the exchange of a few sentences. If a woman likes a man, she may offer more 'filler' sounds like 'ah' and 'oh'. This is also something that men tend to do when they find a woman attractive, but only if the man in question is not shy.

Is parental love innate ?

When people talk about parental love being innate (inborn) they are generally thinking of a mother's love for her child. A father's love, on the other hand, is not generally considered innate, although even the assumption that a mother's love is innate is now coming under closer scutiny. Psychologists and psychiatrists report that mothers have very conflicting emotions about their children. Some mothers can certainly exhibit negative emotions towards their children-in extreme cases even hating them. Ethnologists, historians and folklorists point out that the close mother-child relationship, which is regarded as the norm in today's Western industrialised nations, is a relatively new phenomenon. Because of the expectations that are a part of this bond, mothers can feel overburdened. Among people living in less urban societies, the norm is often for the young to be nurtured by several female relatives.

What turns us into addicts ?

In principle, anything that gives someone a particular thrill can be addictive. If a person's desire to experience the thrill repeatedly becomes overpowering, he or she can be described as addicted. Cravings are typically for substances such as alcohol or nicotine, although it is also possible to become addicted to basically harmless or even socially acceptable pleasures such as chocolate or sport.

Why are people sometimes public spirited and at other times selfish ?

People tend to behave in a socially responsible or even utterly selfless way when they are concerned with the welfare of a group that is close to them, or part of what they regard as their tribe. Kinship appears to play a major role in this. The more closely related people are, the greater their willingness to help or make sacrifices. An example of this is that people are more likely to agree to be organ donors for a relative than they are for a stranger. We are also more likely to help strangers if they look like us, and scientists suspect that this is because we are inferring a genetic similarity. Whether this behaviour is innate or learned is still a question for debate.

Why do people need other people ?

AIthough humans can enjoy being alone for a while, they are not suited to permanent isolation. We know from experiments that people who have spent long periods in total isolation from other humans can even experience delusions and hallucinations. The need for company is probably innate. It is possible that this genetic tendency developed because human children need to be taken care of by their parents for a longer time than the young of other mammals.

Humans by the numbers

Scientists from many fields study human beings and their cultural achievements. Their collected findings can be expressed in some impressive figures.

How many genes does a human being have?

The human genome, with its 3.2 billion DNA building blocks, has now been completely decoded. Only 3% of the DNA contains genes that serve as recipes for building proteins. A few years ago, the number of human genes was thought to be 100 000, but we now know that it is about 25 000.

How large are human cells?

The human body has more than 200 cell types in a range of sizes. Most have a diameter of between 20 and 50 micrometres (one micrometre one-thousandth of a mm). At 120 micrometres, the ova are the thickest, and spermatozoa are the thinnest, with a diameter of only 3 micrometres. The longest are the spinal nerves, which can form branches of up to 1 m in length.

To what length can human hair grow?

The length of a hair depends on its life span and growth rate. Body hair remains short because it drops out after only a couple of months. In contrast, hair on the head generally grows 10 mm a month for about seven years. People with hair several metres long are extreme exceptions. Their hair either grows for an unusually long time or at an above average speed.

How rapidly does food pass through the intestines?  

The length of time it takes for a meal to make its journey through the 8 m or so of the intestine depends on what was in it. Fat and roughage are the contents that have the most influence on the amount of time food spends in the stomach and the rate at which it is transported on from there. Speeds of between 20 and 40 mm a minute are achieved in the small intestine. On average, it takes two to three days for the undigested elements of our diet to complete the journey from mouth to anus.

How much water does the human body contain?

The human body as a whole is made up of 60-70% water. The highest water content-99%-is found in the vitreous body of the eye. Lymph and blood contain 96% and 80% water respectively. The least amount of water even less than in bones (13%) - is contained in tooth enamel, a mere 0.2%.

How long do the body's cells live?

 The shortest lifespan is that of the cells of the small intestine's mucous membrane, which are expelled after only one and a half days- a total of 250 g of cells each day. It takes between 40 and 56 days for a cell to migrate from the bottom layer to the horny layer of the skin, and red blood corpuscles die after 120 days. Depending on type, immune cells can live from a few days to several years, while nerve cells can remain sound for a person's entire lifetime.

How many bones are there in the human skeleton?

The human body has about 206 bones, but it is possible for it to have more. Some people, for example, have an additional, 13th set of ribs or in very rare cases - more than 10 fingers and toes. About half of all our bones are to be found in our hands and feet. Newborn babies have about 350 bones, several of which fuse together later in life.

How many sperm does a man produce?

It takes about 70 days for a mature sperm to develop from its precursor cell. About 1000 sperm per second are produced in the testicles, which amounts to 100 million sperm each day, of which unused sperm are broken down. A millilitre of seminal fluid contains about 60 million sperm. After sexual intercourse they have just three days to reach the ovum before they die.

How many muscles does a human being have?

A human being has more than 600 muscles, which make up 40% of a man's weight and 30% of a woman's. The largest muscle is the broad latissimus dorsi back muscle, and the smallest is attached to the stapes, or stirrup ossicle, in the middle ear.

How many cells does blood contain?

In an adult's 5 1 of blood, there are 50 billion white blood corpuscles, 1.5 trillion blood platelets and 25 trillion red blood corpuscles - together representing one-quarter of the body's total number of cells. More than 2 million red blood corpuscles are produced in the bone marrow every second. If they were laid end to end, they would stretch a distance of 192 500 km-five times about the Earth.

What is the output of the heart?

During low levels of physical activity the heart pumps 4-5 litres of blood per minute, or 6000-7000 litres a day. Some 140-300 ml go into a heart ventricle, 70-130 ml of which are pumped out with every heartbeat. By the time we reach the age of 70, our heart will have beaten about 2.5 billion times and pumped 160 million litres of blood.

How quickly can we react to a sound?

 Human beings react more rapidly to acoustic stimuli such as the crack of a starting pistol- than to any other forms of stimulus. The threshold below which human reaction times cannot go - even following intensive training- is about one-tenth of a second. The minimum reaction time following other forms of stimuli is considerably longer.

How long is 'now'?

The brain seems to operate within periods of time of about 2.5-3.0 seconds in duration. These periods are experienced as being 'now'. If external stimuli remain constant for longer than about three seconds, a human being will feel that something is 'going on a bit'; and if these stimuli stay the same for a long time, boredom begins to set in.

What is the highest IQ ever measured?

American Marilyn vos Savant's IQ of 228 is the highest ever measured. She achieved this score at just 10 years of age.

Which language is spoken by the greatest number of native speakers?

With over 880 million speakers, Mandarin Chinese has the greatest number of native speakers. In addition to Mandarin there are other Chinese dialects, such as Cantonese. This is why the number of Mandarin speakers is considerably smaller than the total population of China.

What is the largest language family by number of native speakers?

Indo-European is the largest language family, if we are counting the number of people who speak one of the Indo-European languages, which includes English, German, French, Italian, Spanish and Portuguese, as well as Russian, Punjabi, Urdu and Hindi. A total of about 2675 million people have one of the languages from this group as their mother tongue.

What is the largest language family by number of languages?

The number of member languages in each of the world's language families varies considerably. The West African Niger-Congo language family, which encompasses some 1514 individual languages, is the largest purely in terms of numbers. By way of contrast, the Indo-European family contains a mere 449 languages.