Schistosomes: beware the water

Over 700 million people worldwide are at risk from parasitic worms called schistosomes (blood flukes), which are transmitted via swimming in contaminated water. The worms are a major problem and can cause a severe debilitating disease called schistosomiasis in their hosts, which, sadly, kills nearly 200 million people each year.

This is an adult male blood fluke. Note its highly developed mouth piece on the right, which is uses to 'clamp' onto the inside of blood vessels and anchor itself against the blood flow. Once secured, it feeds on the nutrients carried in the host's blood. The fold that you can see running through the centre of the worm is called the gynacophoric canal, in which the much smaller female worm lies in permanent copulation.

Due to the large distribution of the schistosomes and their prevalence in third world countries that have very little infrastructure, they are of huge concern to the World Health Organisation, who is trying to reduce the levels of infection by educating people in endemic areas of the dangers, improving sanitation and by ensuring that the drug praziquantel is readily available to as many patients as possible.

Unfortunately, praziquantel treatment is extremely unpleasant and results in a range of negative side effects in humans, including: dizziness, somnolence, seizures, arachnoiditis and diarrhoea. To make matters worse, the parasites themselves actually worsen these side effects and patients undergoing treatment can also suffer from urticaria, rashes and pruritus. This is due to the sheer volume of dead parasitic material that is released into the blood at any one time, which can also cause eosinophilia in leukocytes.

Schistosomes are waterborne and infect human hosts when they swim in contaminated water. As the host swims, they leave a trail of fatty acids from their skin in the water behind them. The parasite is attracted to these fatty acids (L-arginine inparticular) and then attaches itself to the host's skin. Once attached, schistosomes secrete acids and enzymes from acetabular glands and literally burn through the skin until they enter the bloodstream! The distinctive and unpleasant rash that results is often called 'swimmers itch'.

Due to the problems associated with praziquantel, many health agencies are beginning to acknowledge that the best way to combat schistosomiasis is to prevent human infection in the first place. The easiest way to do this is to treat infected waters with insecticides that kill water snails – another vector that is essential to the schistosome life cycle. Without water snails, schistosomes will be completely unable to infect humans and the problem of schistosomiasis is thereby solved!

Like most parasites, schistosomes have an extremely complicated life cycle where they morph through a range of different forms and, at different stages, live in more than one host.

One of the reasons schistosomes are such a major problem is because males and females live in permanent copulation with each other inside the human body so can literally release thousands of eggs in a very short space of time. Rather than the parasites themselves, it is actually these eggs that cause the symptoms of schistosomiasis – a chronic, severely debilitating disease that is usually fatal. The exact symptoms of schistosomiasis vary (depending on the species that has infected the host and where the worms prefer to take up residence), but the most common symptoms are given below:

• Intestinal schistosomiasis is caused by the bowel-living species of blood flukes Schistoma mansoni and S. japonicum, and is associated with abdominal pain, diarrhoea and bloody faeces. Liver enlargement is frequently seen in advanced cases, which leads to gross abdominal swelling as fluid is forced into the host's peritoneal cavity as a side effect of abnormally high blood pressure
• Urogenital schistosomiasis is caused by S. haematobium, which lives in the bladder, and is commonly characterised by haematuria (blood in the urine); lesioning and scarring of bladder tissue; ureter and kidney damage; genital lesions that lead to pain during sexual intercourse; and, in advanced cases, can lead to infertility and a variety of cancers

Liver enlargement is one of the most debilitating symptoms of schistosomiasis and is fatal in almost all cases. This is due to the large-scale, irreversible damage it causes to the host's body.

What makes schistosome eggs so problematic is the large spike that protrudes from their surface. This spike is designed to slice through the walls of blood vessels so the eggs can pass into their hosts urine or faeces (and thereby be passed back into water where they hatch and infect more snails), but can become caught in the host’s tissues upon occasional. Once an egg has become lodged, the host’s immune system identifies it as 'foreign material' and a type of leukocyte called a macrophage activates in response. Macrophages quickly form a granuloma around the egg, which is essentially just a tough wall of inert proteins that prevents the egg from interacting with the body’s tissues. Ordinarily, granulomas are beneficial and are eventually removed from the body, but this cannot happen with the trapped egg. Due to this long-term presence, the surrounding tissue begins to inflame and no longer functions correctly. This problem is exacerbated as an ever increasing amount of eggs build up in the organ and are themselves enclosed by granulomas! Eventually, the organ becomes so blocked and damaged that it is unable to function correctly - leading to the symptoms of schistosomiasis!

Scientists are currently working on a waterproof cream that mask the fatty acids on our skin when we swim (which will help prevent schistosomes from invading our body), but this research is still in its early stages and doesn't look likely to have a practical application anytime soon. For now, you should simply avoid swimming in any water where schistosomiasis is prevalent (no matter how inviting it may look). If you are travelling aboard, such as to Africa (where schistosomiasis is a particular problem), I strongly recommend that you consult your doctor and travel professionals to familiarise yourself with the risks of the area before you head out.

Ghost organs: the future of transplant medicine?

The human body is far from perfect, being at risk from numerous degenerative diseases that 'break' essential organs and lead to our deaths. Aging, disease and poor lifestyle choices are the obvious causes of such organ failure and our current level of science and technology is largely unable to cure such damage.

Organ transplants provide patients with the best hope of survival, in which the defective organ is replaced by a healthy one from a donor. Needless to say, such operations are dangerous and carry high risks of patients' dying during the operation, from the patient’s own body rejecting the new organ and secondary infections (caused by post-surgery immunosuppressant drugs).

Last year, 166 people in the UK went under the knife in heart transplant operations [source]. Needless to say such operations are dangerous and, despite recent advancement in aftercare treatments, 1 in 10 patients will die within the following year. Their body rejecting the new organ is the main cause of these deaths, which kills most patients within the first month from the surgery.

Yet despite the risks thousands of people are on transplant waiting lists all over the world, being desperate for the chance of getting a replacement organ to extend their lives. Improvements in operation procedures and aftercare have reduced the risk of dying during surgery in recent years, but rejection is still a major issue that patients must consider and is something that we are unable to prevent in every case.

Transplanted organs are rejected by leukocytes (white blood cells), which make up our body's natural immune system. All cells have proteins on their surface called antigens, which allow leukocytes to identify 'friendly' tissues. Foreign material has different antigens on its surface which, when detected by leukocytes, causes them to destroy the invading cells. This is usually beneficial and allows us to 'fight off' bacteria and viruses, but in organ transplants the donor actually needs the foreign material to live!

Anti-rejection drugs (which suppress our immune system), have had some success in preventing rejection, but they put the patient at risk of dying from common illnesses (such as colds and intestinal bugs) and aren't successful in all cases. The perfect solution to this problem would be to clone the patient’s organ so their body doesn't recognise it as 'foreign’ material' post-transplantation. But - thanks to all of the media’s unfounded nonsense and scare-mongering about stem cell research - our cloning technology is still a long way off being able to do this. We do have something similar in the pipeline though – ‘ghost’ organs.

This sounds ridiculous, right? But actually it’s not and a ghost organ is simply an organ that has been decellularized. Chemicals that are commonly found in detergents and shampoos are used to ‘wash away’ all of the organ’s cells until only a ‘scaffolding’ of extracellular connective proteins are left. Healthy cells are then taken from the patient and are grown over the connective proteins to repopulate the organ. Once this repopulation process is complete, the donor has a heart comprised of their own cells so rejection is EXTREMELY unlikely!

This is a ghost organ made from a decellularized pig's heart. All of the cardiac cells have been stripped away, leaving only the connective tissue.

If perfected, ghost organs have the potential to be transplant’s equivalent of cancer's 'magic bullet' and may save uncountable human lives in the future. But, despite having repopulated ghost organs with cells successfully, the technology still has its problems and scientists must find a way to make the cells functional if they are to used as replacement organs.

For example, the cells in ghost hearts beat discordantly as individuals, which means they would only pump half the fluid as a healthy heart around a host's body. Obviously, this means they aren't viable for transplants yet and scientists must devise a way to get them to pump in a propagated wave (as healthy heart cells do), before they will be of any medicinal use!

But prominent researchers in this field, such as Dr Doris Taylor from the University of Minnesota, are optimistic and predict that human trials will likely begin taking place in years rather than decades! Ghost lungs are proving to be particularly successful and research is progressing in using ghost organs to replace almost the entire human viscera!

Do we really eat spiders in our sleep?

Urban mythology claims that each year, a certain number of spiders crawl into out mouths while we are asleep and are consequently eaten. While the exact number of spiders that we are supposed to eat varies widely, the common theme remains the same and the stories usually suggest that there is nothing we can do to prevent this from happening.

Spider silk is one of most amazing chemicals in nature, being both incredibly light and having a tensile strength that is far greater than steel. In fact, the silk of the golden orb weaver (not shown above) is 6 times stronger than steel and is 10 times more efficient at absorbing energy than military-grade kevlar, being tough enough to capture bats and small birds!

Whereas it is doubtful that we could stop spiders from crawling or lowering themselves into our mouths if they wanted to (we are asleep afterall), there is actually no need as a spider would not be interested in creeping down our throats, so that in fact, we have nothing to worry about whatsoever!

This is mainly due to the content of our breath, which is warm, humid and has a much higher carbon dioxide to oxygen ratio than 'normal' air does. If a spider was crawling towards our mouth, it would sense such conditions when we breathed over it and would actively avoid them since they signal that the conditions within are mouth are harsher than those outside. Imagine, for example, smelling smoke coming from your living room - even if you couldn't see or feel the flames, you would know that something was wrong and that there may be a danger in the room. Thus, you would most likely avoid going in!

For similar reasons it is unlikely that a spider would want to enter your mouth and, if one was on your face, would probably turn tail and run once it came close enough to feel your breath!

Age of first sexual encounter may effect relationship happiness and success in later life

It is widely accepted that modern society runs at a faster pace than it used to, with children and teenagers experiencing many life events at much younger ages than did their parents and grandparents. This 'growing up fast' way-of-life is of great concern to many parents, especially when their children's ventures into sexual relationships are concerned, who are worried that their children are not ready such encounters. Is there really a cause for concern, however, or are parents just fussing and worrying for nothing?

Humans are a very social species and, in resource-abundant environments, usually favour a mating pattern called monogamy, where one person has just one sexual partner for a long period of time. Such relationships are rewarding and healthy when they work, creating stable conditions in which to raise a family.

Recent research from the University of Texas has suggested that, unfortunately, there is. The study, which was carried out by psychologist Paige Harden, has tried to determine whether the timing of an individual's first sexual encounter affects their romantic relationships later in life and whether it can predict factors like relationship satisfaction, the likelihood to marry and the number of sexual partners.

Dr. Harden conducted this research via a meta-analysis, using data from the [US] National Longitudinal Study on Adolescent Health and followed 1659 people from their early teens to young adulthood (<29 years old). As part of this research, Harden classified each participant in one of three categories in regard to their age at their first experience of having sexual intercourse: Early (<15), On-time (15-19) or Late (>19), before comparing the qualities of their romantic relationships/encounters.

As she predicted, the most highly educated participants from greater income families were older at the time of their first experience of sexual intercourse. The study appears to show that first experiencing sex at a later age is beneficial to an individual, as those in the study showed greater levels of marriage (or living with their partner), were less likely to be dissatisfied with their partner, were less likely to persist in an abusive relationship and typically had less sexual partners over the course of their life.

In contrast, those who were younger at their first encounter tended to have many more sexual partners and typically showed a greater level of romantic dissatisfaction. This data also fit with a clear pattern: those in the 'Early' group showed much more exaggerated trends than those in the 'On-Time' category.

Dr. Harden explains these results by suggesting that waiting until later to first have sexual intercourse may be beneficial to an individual as it allows their cognitive and mental development to have finished first. As well as having obvious benefits such as greater confidence, which makes an individual more likely to walk away from abuse and inappropriate pressure, being fully developed [mentally] also appears to enable an individual to learn more 'healthy' relationship skills. Harden suggests that it is these skills in particular that allow an individual to form healthier and happier relationships, which are more likely to endure for longer periods of time.

Although these findings are worrying, and seem to show that being young when having sexual intercourse for the first time can have series and long-term negative side-effects,  more research needs to be carried out into these ideas before any significant statement can be made. Dr. Harden has acknowledged this, saying that "we are just beginning to understand how adolescents' sexual experiences influence their future developments and relationships". For the time being, however, it looks like parents are right after all, and children may indeed, be 'growing up too fast'.

From black to white: is calcium really that important?

The majority of us are at ease with Darwin's concept of evolution and understand how the 'survival of the fittest' has led to the vast abundance of life on Earth. Obviously, humans are no exception to this rule and evolution has moulded us into what we are today. Evolution, for example, selected for the first of us who began to move on two legs as this freed up our hands for better tool use; and selected for those who chose to live in social groups, which provided much more protection and help than did living alone. Without evolution it is doubtful that any life would exist on Earth at all, especially not in the form of hugely sophisticated organisms like humans.

Life on Earth began sometime around 4 billion years ago. It is believed that single-celled organisms first evolved on the shores of primordial oceans, which were abundant in the resources needed for life. Over time, these cells eventually evolved into the countless forms of life that we see on Earth today.

Most of you won't be surprised by any of this; it makes sense, after all. Something you might find surprising however, is why scientists believe that the early humans settling Europe evolved from being black to white. Obviously the sun's rays are less intense in Europe than they are in Africa, meaning that European settlers wouldn't have needed to produce as much of the pigment melanin in their skin, which absorbs ultraviolet (UV) radiation. Producing less melanin then would have provided such individuals with an advantage as they wouldn't have been wasting energy producing proteins their body didn't really need. This saved energy could then have been dedicated to more important processes (like keeping warm in the colder climate, for one thing).

Although this theory makes sense logically and saving energy by producing less melanin could quite plausibly have been the difference between life and death in the harsh European winters, is it really enough to have driven the evolution of one of our most noticeable racial polymorphisms?

Many scientists believe not, at least not by itself anyway, and research into this question has provided a rather odd alternative. Simply put, many scientists now believe that Europeans evolved from having black skin to white skin due to calcium!

Calcium is an fundamental resource for our bodies, with its ions having essential roles in muscle contraction; in propagating nerve impulses; and, arguably most importantly, in forming our skeletons (via binding with phosphorous to form a very stable salt called calcium phosphate). Despite its importance, calcium is rare in nature and is extremely difficult to acquire naturally as part of our diets. As always however, Nature provided early man with an ingenious way around this and all humans are able to make vitamin D in their skin when it is exposed to sunlight (in much the same way as plants photosynthesise sugars from sunlight to use as energy). Vitamin D greatly increases the affinity of calcium absorption in the gut, allowing the body to absorb much more of any calcium that it consumed than it would otherwise be able to.

Due to this ability, most people are able to acquire enough calcium (especially during the summer) to lead normal and healthy lives, and indeed, our African ancestors would have had strong bones and efficient muscles. The problems arose however, when early explorers entered Europe where the sun's rays are much less intense. This meant that the melanin pigments in their black skin were able to absorb much more sunlight than they could while in Africa and, as a result, vitamin D could no longer be produced.

Fossil evidence suggests that it was not long before the health of these explorers deteriorated, and many adult skeletons from the period show symptoms of osteomalacia (a disease where bones soften due to lack of calcium and deform under the weight of walking), and many may have suffered from a range of muscle weakness and epileptic disorders as their reserves of calcium were depleted and less and less could be replaced from bone stripping. Obviously such ill effects greatly reduced an individual's chances of survival and those with slightly lighter skin would have been more likely to live longer. Being healthier and living longer meant that they would have been more likely to survive to reproduce and slowly, the 'lighter' genes (which produced less melanin), would have spread through the population. In each generation the palest individuals would have been most successful at surviving and breeding so, over time, European humans would have got paler and paler until their skin was as white as it is in their descendants now.

As if this selection pressure wasn't enough to drive for whiter skin, having low levels of calcium and brittle bones had another major problem for women in particular - it hindered childbirth. Many women had such brittle pelvises that they broke under the strain of labour, virtually guaranteeing that both the infant and the mother would die. Furthermore, many children suffered from severe rickets due to a lack of calcium during childhood and puberty. This meant that such individuals were physically smaller than they should have been and many women suffered from underdeveloped hips that were too narrow for a baby to pass through. As a result, such a mother and her baby would have died during labour. Thus, many of the darker individuals would have been unable to give birth so that the darker genes disappeared from the European populations very quickly - being strongly selected against by Nature!

The degree of deformity that rickets can lead to can be very extreme, almost completely debilitating a child suffering with the condition throughout their entire life.

Scientists also believe that this explains why the vast majority of Europeans (and those in their descendent colonies such as Australia and the USA) can eat dairy as a stable component of their diet. This is actually quite abnormal, both in the animal kingdom and among other ethnicities of humans, as rennin (the enzyme required to digest milk) usually stops being produced by the body in infancy after the individual has been fully weaned. Thus, most humans are lactose intolerant and experience unpleasant symptoms if they drink milk or eat too much dairy-based produce. Humans evolving in Europe however, needed as much calcium as possible and would have been under strong selection pressure to continue producing rennin throughout their lives as milk is an unrivalled source of calcium.

Thus, the importance of calcium to the human body has made it an invaluable component that we need to survive. Too little calcium leads to severe health conditions that are so extreme that they can even drive evolution into turning black humans, who have very active melanocytes (melanin-producing skin cells), into white humans who have very little sun-protective pigments in their skin (allowing them to produce more vitamin D).

Sleep: what is it & do we really need it?

In his novel The Wise Man's Fear, Patrick Rothfuss says that "you never really appreciate sleep until you wake up". He makes a good point here, as we often don't want to sleep even though we know that we'll be bad tempered, tired and miserable over the next day as a consequence. This is mainly because we have better, more interesting things to do so spending 8 - 10 hours asleep* seems like a pointless waste of our valuable time. However, as we all know, sleep is essential and shouldn't really be cut back on unless it's completely unavoidable. For example, sleep allows the levels of neurotransmitters in our brains to recover after a hard day's activity, allows us to repair damaged tissue and is even an essential factor for effective weight loss!

In order to fall asleep your core body temperature must drop. Sadly, this means that the traditional British tradition of taking a 'nightcap' of a spirit before bed actually makes it harder to fall asleep as alcohol raises the core body temperature.

As you would expect for such an obviously important biological process then, sleep has been extensively researched for decades. Much of this research has been fairly mundane, revealing fairly obvious facts like our sleep cycle runs as a circadian rhythm (one that repeats itself every 24 hours) and that lack of sleep has negative effects, such as reducing our mental and motor functions; our ability to cope with new and unexpected situations/events; and (usually), causes us to put on weight. Other areas of research however have been much more interesting and have yielded more titillating results.

Research into the sleep cycle itself is one such area, and has found that humans have 5 different stages of sleep. These stages fall into two major categories: Non-Rapid Eye Movement (NREM) sleep, which is sometimes called 'quiet sleep' and Rapid Eye Movement (REM), which is also called 'active' or 'paradoxical sleep'. NREM sleep consists of 4 of the 5 stages of sleep, which are designated as Stage 1, Stage 2, Stage 3 and Stage 4 respectively. REM sleep, which is arguably the most important state, only forms our final and deepest stage. Our bodies cycle through these stages over the period that we are asleep, with each stage being significantly 'deeper' than the one before it. Obviously then, we are much more awake in the earlier stages than in the latter, which is mainly due to differences in the brainwave patterns used by our brains. The earlier stages produce short, fast brainwaves called beta waves, which eventually progress into slower alpha waves. During these early stages, when you're not quite asleep, many people experience intense sensations called hypnagogic hallucinations. These are perfectly normal, and common examples include the sudden sensation of falling and hearing someone calling your name. Many people also experience sudden starts in the early stages, where they wake up with a twitch for no apparent reason. These starts are called myoclonic jerks and are not a cause for concern in most cases.

It is worth noting however that the body does not progress through these stages sequentially and upon falling into sleep, the body enters Stage 1. After this it progresses through to Stage 2, Stage 3 and Stage 4, which makes sense really. However, before entering REM, the body reverts back into Stage 3 and then Stage 2. It is only after reaching Stage 2 for its second time that the brain jumps directly into REM sleep. After the body has finished with REM sleep it returns back to Stage 2, which forms one complete cycle and typically takes 90 minutes. Our bodies typically undergo 4 or 5 of these cycles every night (consecutively) and spend more time in REM and less time in NREM sleep with each cycle. Thus, the body spends only a short amount of time in REM at the beginning of the night, but by the end, can be in it for up to an hour at a time.

The invention of the electroencephalograph in 1924 allowed scientists to see a person's brainwaves in real-time. Thus, it allowed them to study sleep as they never could have before and led to the discovery of the 5 stages of sleep.

Although this sleep cycle seems overly elaborate and pointless (as we're only asleep), it is actually very clever and each stage has its own characteristics and biological functions. Stage 1 for example, can be considered as our gateway into and out of sleep and typically lasts for only 5 - 10 minutes. Stage 1 is characterised by high amplitude theta waves in the brain, which are a very slow type of brainwave and, if a person is woken during this stage, they probably won't even realise they were asleep because their brainwaves are very similar to those displayed when they are awake.

Stage 2 last for up to 20 minutes and can be compared to a 'track changer' on a rail-road system and directs our brainwave patterns back into Stage 1 (so that we wake up), further in NREM sleep or deep into REM. Therefore Stage 2 effectively controls the sleep cycle and is characterised by the appearance of rapid, rhythmic bursts of brain activity called sleep spindles. It is in this stage that our core body temperature and heart rate begins to drop, which lowers our metabolism and energy consumption to allow our breathing to slow.

Stage 3 is a transitional period between light and deep sleeps and is marked the the appearance of delta waves, which effectively prepares our minds for low-intensity dreaming. Stage 4 follows on shortly after the appearance of delta waves, and is the first stage in which we dream. Stage 4 typically lasts for about 20 minutes and is the most likely stage for bed-wetting and sleepwalking to occur in.

Most of our dreaming occurs in REM, which, as mentioned before, is our final and deepest stage of sleep. This also explains why we rarely remember of dreams in REM even though it is here that they are at their most vivid - our brainwaves are so completely different to the patterns our brains use when we are awake, that they are almost completely incompatible with each other! Think of the difference between video cassettes and DVDs, which both show the same media despite doing in completely different ways...

Bizarrely our bodies actually become more active in REM sleep than in NREM, which is why it is sometimes called 'paradoxical sleep'. This can be seen just by looking at someone in REM as their eyes flick around in their sockets very rapidly, which gives the stage its name. To prevent people thrashing around in their beds and acting out their dreams our bodies employ a clever trick: they secrete a chemical that paralyses all of our voluntary, skeletal muscle so that we are unable to move!

Alarm clocks that wake you up using light are much better since they cause your brain to cycle down through its sleep cycle so that you wake up directly from Stage 1. This is the 'natural' way to wake up and leaves you feeling alert and fresh, as if you'd woken up by yourself. Sound alarm clocks can wake you abruptly from any stage, which is a problem when you are woken from the deeper states. This is because the deeper states have brainwave patterns that differ greatly to waking patterns, so that you feel groggy and disorientated for a time until they have changed.

An addition to understanding what goes on when we sleep, much research has also begun to unravel why we need to sleep in the first place, finding it to be essential for our long-term health. There are three main theories of why we sleep that do not have antagonistic values with each other, so may all be correct to varying degrees. The first, and probably most accepted theory, is called the 'Repair and Restoration Hypothesis'. This theory suggests that our bodies use sleep to heal and repair any damaged tissues and restore all of the physiological processes that allow our bodies and minds to function efficiently. Studies into this theory have found that people spend more time sleeping after periods of strenuous mental or physical activity, which would be expected really if our bodies were indeed healing during sleep. Research has found that the body greatly increases the rate of cell division and protein synthesis during NREM sleep, which is essential for growth (in a child) and for repairing physical trauma. Evidence also suggests that the high brain activity seen in REM sleep allows the body to replenish and 'restock' its levels and reserves of neurotransmitters so that the brain can function more easily and efficiently the next day.

The second major theory of sleep suggests that it is a mechanism for the brain to make sense of and store all of the information and events that it has been exposed to throughout the day into the brain's long-term memory. This is called the 'Information Consolidation Theory of Sleep' and research has provided much evidence that supports it.

Many students, particularly when at university, pull 'all-nighters' where they spend as much of the night as they can revising for their exams. This is actually detrimental to their learning efforts and makes them much less likely to remember what they've read. Having an early night greatly increases the likelihood of the information they've revised earlier being stored and makes it easier for them to think the following day.

The third and final of the major theories is called the 'Evolutionary (or Adaptive) Theory of Sleep' and suggests that sleep is used as a mechanism for conserving energy (due to decreased physical activity) during periods in which it would be dangerous for that animal to be active in, such as at night in humans due to our relatively poor ability to navigate our environment in the dark. The main support for this theory comes from the fact that animals with few or no natural predators, such as lions, sleep for much longer periods of time than those with many predators, such as mice, which only sleep for a few hours a day.

So, it is obvious that sleep is an essential and a very important process for our health. It allows us to conserve energy, repair damaged tissue, helps us to form long-lasting memories and helps to us prepare for the days to come. Skipping sleep in favour of other, more interesting activities, really isn't a good idea and you should ensure that you are getting the amount of sleep that your individual body requires each night. All of the sleep-deprivation studies to my knowledge associate a lack of sleep with direct, negative side-effects that can easily be avoided.

* on average, depending on your age.

Do our hair and nails really grow after we are dead?

Many people will tell you that once you have died your hair and nails will continue to grow for days afterwards, with the exact time period varying depending on the individual telling the story. This popular piece of 'common fact' is undeniably interesting, but sadly, is completely incorrect; being nothing more than a frequently repeated tale of urban mythology. To put it simply, when you are dead your metabolism has completely ceased and among many things, this means that your body cannot create any new material like hair and nail tissue.

This is an electron micrograph of a human hair follicle. Hair is formed from rapidly dividing skin cells that are killed almost as soon as they are formed and filled in with a insoluble biological 'wax' and colouring pigments. They are then wrapped up a bundle of keratin fibres to form a helical strand of hair. The strand then grows from its bottom as new cells push the older ones upwards. Nails grow in much the same way, except they are laid down in sheets rather than as a helix.

Yet despite this, a deceased person's hair and nails do appear to grow for nearly a week after they have died... Although this may appear confusing at first glance, the answer to the conundrum is in fact very mundane: the human body is predominantly composed of water and over time, a cadaver dehydrates. As the cadaver looses water into the surrounding environment, their skin contracts and exposes already grown (but previously hidden) hair and nail tissue. It is surprising how much of these materials your body has tucked away beneath your skin and, by contracting, gives the impression that they are eerily growing post-death on their own accord...

Dehydrating skin also explains another common feature of corpses, whereupon they appear to smile. As the skin around their mouth becomes tighter it contracts and pulls the lips away the mouth, giving the impression of a somewhat grotesque smile.

Thus the simple action of water moving out of our bodies after our death has instigated confusion for hundreds of years, giving rise to a popular story that many people incorrectly believe as fact!

New drug could save countless lives!

Scientists from Queen Mary, University of London, have recently announced that a new drug is in the pipelines that could potentially slash the numbers of fatal and debilitating cases of heart attacks and the ailments associated with high blood pressure/cholesterol each year. The drug, which has not yet been named commercially, is a 'polypill' formed from a statin (a class of drugs that lower cholesterol) and three drugs that lower blood pressure. All of the polypill's components have been used pharmaceutically for decades so that the new drug is considered safe, although any risks or side-effects that may be associated with its use cannot be determined until large-scale testing has been carried out on human volunteers.

The various drug components of the polypill are ground into a fine powder and mixed within an insoluble shell (that is often based on glycerol), which is broken down by enzymes secreted in the small intestine.

The scientists developing the pill have called for it to be made available as "a matter of urgency" and expect the pill to be available upon prescription within two years. Should this be the case, then the drug may reduce the blood pressure of over 50's by 12% and their 'bad' cholesterol (formed by Low-Density Lipoproteins) by 39%. This effectively reduces their likelihood of having a heart attack or a stroke for example, to the same levels of risk experienced by reasonably healthy 20 years olds - preventing an estimated 94, 000 a year!

Although the polypill has been heralded as a "milestone" in our ability to help fight these illnesses, which are becoming disturbingly more and more common, they are not a substitute for healthy living. The British Heart Foundation (BHF) stresses that although the positive benefits of the drug are obvious in the small-scale study carried out to provide this data, much more research into its application and effects needs to be carried out before the drug is ready for production. Particularly on the long-term effects of the drug on healthy people, who may buy it in order to stave of such conditions.

Despite the misgivings arising from the drug's lack of testing, the commercial use of this polypill looks likely. Combined with a balanced diet and healthy lifestyle, the drug could save up to 200, 000 lives in the United Kingdom every year and greatly reduce the numbers of patients suffering from permanent disabilities resulting from strokes.

The curious case of the Honeyguide

According to rock paintings scattered throughout Africa, humans have been collecting honey for at least 20, 000 years. This is not surprising really seeing as it is a readily available and palatable food that has a sweet taste and high energy output. What is surprising however, is that many African tribes (which still collect honey using traditional techniques), frequently work in partnership with a bird that leads them to any bee colonies that it has discovered in trees, rock crevasses and disused termite mounds! There are anecdotal records of this partnership extending as far back as the 17th Century - a partnership that has been of great interest to many biologists.

The Greater Honeyguide, Indicator indicator, is related to the family of woodpeckers and is native to sub-Saharan Africa.

This remarkable partnership between the Greater Honeyguide and humans is fairly complex and requires the active participation of both parties in order for it to work effectively. To begin it, African honey-gatherers first draw the attention of the bird when they set out on an expedition by using a distinctive whistle that can be heard from more than a 1 km away. This call, known as the 'Fuulido' among the Boran tribes of Kenya, is made by blowing air into closed fists, modified shells or hollow nuts and more than doubles their chances of encountering the bird. Once a Honeyguide has located humans that are interested in foraging for honey, it becomes excited and flits rapidly between perches that are close to the party while emitting a double-noted and persistent call. African honey-gatherers claim that this call signals that the bird knows of a nearby bee colony, which it will lead them to. Thereafter this behaviour, the Honeyguide flies away in a straight line for up to few minutes before returning. Once it has returned to the foraging party it sits on a conspicuous perch until the honey-gatherers approach it, at which point it flies off again in the same direction (while calling). In this manner, it leads the humans to the site of the colony with each flight getting shorter and each perch getting lower as the distance to the hive decreases. Once the Honeyguide has reached the site of the hive, it circles it and emits a lower 'indication call' that is softer, with a greater gap between notes to signal their arrival.

Researchers have found that this communication system is extremely successful and have calculated that by following the bird, African honey-gatherers can reduce their foraging times by 64% (Isack & Reyer, 1989)! Despite its obvious success and benefits to humans however, many scientists were once baffled as to why the system evolved in the first place. Mainly, because it would have been an evolutionary nightmare: with both counterparts to the system having to learn how to communicate with the other and what parts to play simultaneously... It is plausible however when you consider the fact that humans and Honeyguides have coexisted in Africa for millions of years, providing a long 'window' that this could have taken place in. Furthermore, the evolution of such a system makes sense logically. Humans benefit from following the Honeyguide since the bird leads them to bee colonies and saves them many hours that they could have spent fruitlessly searching for. Once at the nests, humans can break them open using tools and smoke (an old bee-keepers trick that makes bees very docile, effectively sending them to sleep) to extract the honey and thus, get a food reward. The Honeyguide benefits from leading humans to any nests that it has found since humans can break the nests much more easily than they can. Thus, they can get their own food reward (wax and larvae) without the risk of being stung. Thus, both parties directly benefit from participating in the arrangement and it should logically, be under positive selection pressure.

Many biologists argue that the communication system between humans and the Honeyguide actually evolved between the bird and the Honey Badger, Mellivora capensis, and that humans merely 'hijacked' their way into it. This is highly doubtful however, due to two main reasons. Firstly, Honeyguides are diurnal (active during the day) and Honey Badgers are nocturnal (active during the night) so the animals would rarely meet under natural circumstances and definitely not enough to allow such a sophisticated communication system to have evolved. Secondly, because no-one has ever seen a Honeyguide lead a Honey Badger to a bee colony nor are there any historical anecdotes of this occurring.

Interspecific communication systems such as this are very rare in nature and have only seldom evolved. This is mainly due to the fact that different species are usually in direct competition with each other for resources so would normally selfishly exploit such a system for their own ends and due to the difficulties in the genetics and learning that underlies such behaviours (which were mentioned earlier). Thus, the relationship between humans and the Greater Honeyguide is a remarkable feat of communicative engineering and is a superb example of the ingenuity of Nature.

Reference

Isack H. A. & Reyer H. U. (1989). Honeyguides and Honey Gathers: Interspecific Communication in a Symbiotic Relationship. Science 243, 1343-1346.

"I spy with my AMAZING eye..."

Human vision is incredible, with our eye being one of the most sophisticated structures for capturing light that has ever evolved. Our eyes are capable of detecting a single photon of light at night and can create complex and unbelievably definite images during the day, being able to make out structures 1/10th of a hair-span wide. Our eyes allow us to see the world in a detail that almost no other mammal (or animal) can imagine and, since humans rely mostly on our vision to interact with and perceive the world, are extremely important to our survival and quality of life.

Although light is detected by the eye, and is essential for it to function, too much light can be very damaging to our vision. Thus the size of the pupil, the black hole in its centre where light enters, can be controlled by the iris that surrounds it. The iris contains light absorbing pigments and determines how much light can enter the eye. The eye ball itself is protected by being shrunk back into its socket, with our brow protruding over it to reduce the likelihood of it being physically struck. In addition, our eyelids have eyelashes that help to stop dust and debris from falling onto its surface.

The human eye is classified as a 'lens eye', since it forms images using a biological lens that is suspended behind the pupil. Lens eyes are the most complex form of visually perceiving light and have only evolved in primates, birds and some Cephalopods (squid and octopuses), being unique in their ability to alter their focus to produce crisp images of close up objects and those that are much further away. Most organisms have a 'fixed focus' system where any object that is not at a certain and specific distance from their eye will appear blurred. The lens makes this focus possible by bending the light that passes through it so that it is refracted neatly onto the fovea (which is at the centre of the macula), at the back of the eye. The fovea is a small area of the retina where the light receptor cells that make make up the retina are particularly dense, and produces the most detailed image of our surroundings. Thus, by becoming thicker for closer up objects and thinner for those further away, the lens can refract light so that most of it lands on the fovea and a sharp, clear image is formed.

To focus on close up objects the lens is made thicker so that its refractive power is increased. This is accomplished by a contraction of the ciliary bodies so that the tension on the suspensory ligaments is reduced. This means that they pull the lens less taught and it contracts. Likewise, to focus on far away objects the converse is true: the ciliary bodies relax, causing the suspensory ligaments to tighten and the lens is pulled upon, stretching it out. This then decreases the refractory power of the lens and light is bent less.

The mammalian visual system is made up from 2 different types of photoreceptor cell: cones, which are responsible for seeing colour during the day (or in other conditions of high light intensity); and rods, which work in 'black and white' and are responsible for our night vision. These photoreceptors contain 4 different photopigments that split when photons of light hit them, producing an electrical charge. This charge is then magnified into a nerve impulse and is sent to the optic chiasm in the brain (via the optic nerve), where it is collated with other impulses from the eyes and processed to form an image. The type of photopigments present in the photoreceptor depends upon its type. Rod cells only contain rhodopsin, which is made from vitamin A (the reason why carrots, which are high in vitamin A, can improve your night vision). Rhodopsin is very sensitive and can detect a single photon of light, responding best to light at 498nm. Although this isn't enough to form an image, it shows just how sensitive human eyes are and explains why our eyes sting when we go from the dark into the light: the sudden increase in light intensity splits all of the photopigment and prevents it from being reconstructed. This is known as 'bleaching' and takes about 15 minutes to be reversed, which is why it takes your eyes a while to adjust to seeing in the dark. Rod cells show the opposite distribution to cone cells and are less concentrated in the fovea, becoming more abundant towards the edge of the retina. Thus, human night vision is at its best in its periphery and objects often become less clear to us in the dark when we look at them directly! This fact is how many scientists explain those incidences where you seem to see something out of corner of your eye that vanishes when you look to see what is was...

The remaining 3 photopigments then, are involved in colour vision and work together to form the 'pallet' of colours that humans can see. This complimentary system is called a trichromatic system and each photopigment responds best at a different wavelength of light, so that most of the electromagnetic spectrum is covered. Long Wave Sensitive (LWS) opsin responds best to wavelengths of 564nm and sees red light; Medium Wave Sensitive (MWS) opsin responds best to wavelengths of 533nm and sees green light; and Short Wave Sensitive (SWS) opsin responds best to wavelengths of 433nm and sees blue light. The brain mixes the signals coming from the 4.5 million cone cells in the retina of each eye and produces colour. Interestingly, this is the same system that early (tube) colour television sets used to form colour picture! They used thousands of units of 3 triangles placed side-by-side that were coloured red, green and blue respectively.

Many nocturnal predators, such as canids and felids (like the cat in this picture), possess a reflective layer of cells beneath their retina called the tapetum lucidum. These cells reflect light back through the retina so that each photon is detected twice. This greatly improves their night vision and explains why their eyes seem to glow in the dark.

However, despite human vision being one of the best visual systems in the world that allows us to see with a clarity experienced by very few other organisms, it is fundamentally limited. This is believed to be due to a phenomenon called 'nocturnal bottlenecking', which occurred over millions of years during the rein of the dinosaurs. Due to the size and ferocity of the dinosaurs the mammals present in this era remained very small and were only active at night to avoid predation. This meant that many genes for colour photoreception were lost, since they were not needed and were not selected for. Thus, the mammalian colour visual system had to be 'rebuilt' from only the 3 photopigments that we had left when the dinosaurs had died out and we began to display diurnal activity. This unfortunately means that our perception of the electromagnetic spectrum is very limited and, as a result, mammals cannot see infra-red or ultraviolet light (UV) light like many of the organisms in the other classes of animals.

However our evolution on the flat African savannah plains has helped to compensate for this and we have  developed a fantastic visual system, which evolved as our primary sense. Our visual system is far superior in terms of quality to that of most other organisms, even if we cannot perceive as much of the electromagnetic spectrum as them; and personally speaking, I would much rather be able to see in higher quality than in more colours so our bottlenecking may actually have worked out for the best!

Humans: the world's only super predator?

Everyone is familiar with how predators and prey interact with each other - predators try to eat prey species and prey species, which do not want to be eaten, fight back or run away. These interactions have led to an 'evolutionary arms race' between predators and prey: where predators evolve adaptations, such as weapons, to help them kill their prey; and their prey evolve defences to counteract these weapons.

A good example of this is the cheetah, which has evolved to be able to run extremely quickly in order to catch gazelle, their main source of prey. Gazelle have worked out that they cannot outrun cheetahs, which are the fastest land-animal, so instead have evolved to be able to abruptly change direction whilst running. This allows them to be able to twist and turn even when sprinting and helps to protect them from cheetahs, which can only run in near enough straight lines. Furthermore, cheetahs are under a great deal of strain whilst running and their core body temperature rises extremely quickly so they cannot run for long periods of time. Consequently, gazelle have also evolved to be good long-distance runners, with most of their muscles being made from fast oxidatve fibres, which allows them to run for much longer than cheetahs can. As the next step in the evolutionary arms race it may be predicted that cheetahs will evolve to be able to run for longer or develop greater manoeuvrability whilst running, allowing them to be able to hunt gazelle more efficiently.



A cheetah chasing a juvenile gazelle. The cat can reach speeds of up to 75mph during the chase and will try to knock the gazelle over, allowing it to grab the underside of the gazelle's throat and suffocate it.

Arms races such as this example are common and exist in some form or another for every species of predator and prey. This is expected by scientists and obviously, makes evolutionary sense. What does not make sense however is that although humans have been around for 2 million years, in which time we have hunted other animals extensively, we do not appear to be engaged in this arms race. We have evolved no specialised weaponry to hunt our prey and none of the species that we prey upon have evolved abilities to defend themselves against us.

Many scientists believe that this is due to the unique way in which we hunt our prey. As I'm sure you know, humans are extremely intelligent and we have always used this intelligence to help us hunt other animals. Our brains have allowed us to create a large variety of tools to overcome our lack of physical weaponry and to develop innovative tactics to overcome our prey's defences.

One such ability of ability of humans is that we are able to throw much more efficiently than any other living animals - both in terms of power and accuracy. Therefore once our ancestors had invented spears, the once cutting-edge technology, we were able to kill our prey from a distance by throwing it - the ability to kill from a distance is unique to us, no other animal is able to do this! Our ability to kill animals from a distance meant that we have had no need to develop weapons such as poisons, claws and large teeth and our prey has not had the opportunity to develop resistance to such a hunting method. This is partly because once an animal had realised that we could kill it, it is already dead and cannot pass its genes on, which is the mechanism by which evolution works. Our intelligence has also meant that we could fashion dull clothing and refine our tactics to sneak up on our prey, so that we have not needed to evolve camouflaged skin either. In fact, the main physical adaptations that throwing would have selected for is strong shoulder and leg muscles and good binocular vision (predators have eyes that are mounted on the front of their head, which gives more precise vision and better depth perception), both of which humans have.

Tribesmen throwing spears. Note how the men are standing sideways, holding the spear in their right arms. When they throw their spear they twist their body around. This greatly increase the force of the throw by using the torque generated in their hips and shoulders.

Human intelligence and the fact that we hunted in packs has also meant that we were able to overcome the  'ten times larger' rule, which is where large terrestrial herbivores that grow ten times heavier than their largest predator become safe from predation, since their predators are unable to develop jaws strong enough to kill them. This explains the large size of elephants for example, and why the adult individuals of such species have no natural predators other than man - simply put, they are just too large for predators for hunt and the risk of injury to the predator is too high! Our ability to hunt animals much larger than ourselves helped the rapid spread of humans across the globe and allowed us to live in areas that would have otherwise been uninhabitable, such as the cold tundra of Northern Europe and Siberia. Human colonisation of tundra climates was possible due to the presence of mammoths, a species of megafauna, for two main reasons. Firstly, mammoths had no natural predators until we arrived, so that we did not need to complete for them with other predators; and secondly, because of the enormous amount of resources than we could harvest from each individual. These resources included meat for food, fur for clothing and vitreous humour from their eyes to make glue. Unfortunately mammoths, like most species of megafauna, had evolved with immunity to their natural predators and consequently, had few defences other than their size. This meant that we were able to kill them very easily and sadly, we drove them to extinction. The extinction of megafauna is a characteristic of human colonisation in new areas and most giant species became extinct around 40 million years ago.

An artist's impression of a group of early humans hunting a mammoth.

Our ingenuity has also meant that humans have been able to overcome most of the poisons that many animals use as defence mechanisms. The most common ways that we do this is by cooking the animal before we eat it, which causes the poisons to break down; or we can remove the poisonous tissues, which is possible because defensive poisons are often concentrated into certain organs, such as the liver. Thus, humans can kill and eat many animals that are avoided by other predators.

Therefore humans are remarkable hunters, being the only animals that can kill others from a distance, kill species much bigger than ourselves and can remove poisonous toxins from our food, which greatly increases the scope of our diet. Thus, it may be fair to say that humans are not merely predators, but are in fact super predators and that we are the most effective and efficient killers that have ever lived.