Can Crocodiles Cry? E-Book

Paul Heiney

• Herausgeber: The History Press
• Kategorie: Lebensstil
• Sprache: Englisch

Seitenzahl: 279

Veröffentlichungsjahr: 2014

Beschreibung

In Can Crocodiles Cry?Paul Heiney unravels further science behind those things we take for granted, and explains just why the world and its contents are the way they are. Drawing on questions asked by the public, this book brings some of the finest scientific minds to bear on how the laws of science apply to everyday life. It is the perfect gift for the insatiably curious, provocative poseurs, quizaholics and science addicts everywhere.

Leseprobe

Contents

Title

Introduction

Animal Magic

The Human Body

What on Earth?

Science in my Life

Spaced Out

Food for Thought

On the Move

The Really Big Questions

Copyright

Introduction

Ask any gold miner and he’ll tell you that the deeper you dig, the better the chances of finding riches. I’m beginning to feel like that gold miner, because for a few years I have been digging deep into a vast scientific archive, and it’s true – the gold not only keeps appearing but it seems to get better every time I excavate. Its richness comes in the form of questions asked by thousands of young people who simply wanted to satisfy their curious minds. The answers, in return, came from a gang of dedicated scientists, all specialists in their fields, who simply wanted to give young people the satisfaction of an explanation of what was puzzling their minds.

It was inspired by a government project to encourage scientific curiosity, and it was hugely successful. It was called ‘Science Line’ and over a few years it was inundated with questions on everything from black holes to space travel; frogs to frostbite; cats to cataclysms. You name it, there was no subject that the enquiring minds didn’t direct themselves at, and no subject the experts did not dare to tackle.

It was good fortune indeed that when the project closed the vast database of knowledge was not destroyed. Instead, like that gold miner, I have been digging deep into it to bring you, once again, some of the gems it contains.

My first harvest was called Can Cows Walk Downstairs?, but those 300 questions hardly skimmed the surface. Then came Do Cats Have Belly Buttons?, and still the questions were being unearthed. Now I offer you Can Crocodiles Cry? to prove that there is no end to the riddles that a scientific mind can come up with.

However, in amongst the inspired, thoughtful and sometimes plain crazy questions, I did find one message from someone who was clearly having a bad day. In a moment of bad temper, he bashed out the following message: ‘My Dad says that science and finding out things is a lot of fun. I don’t agree.’ So, how do you persuade someone that they’re wrong about science? This is the reply he got, and I couldn’t agree more. Read it carefully, even if you think science might not be your thing, and see if you change your mind:

I think science is very exciting or I wouldn’t spend my life doing it. I love my job and couldn’t imagine doing anything different. I’m constantly finding out new things and learning about different subjects so I never get bored. However, I can remember a time when I found some bits of science boring. When I was at school for example, I found some bits of science boring because I had to do them and wasn’t interested in them at the time. If only they’d teach me something I wanted to know.

I can understand that some people might not be interested in science – that’s fine. I’m not particularly interested in football, and I don’t think I’d enjoy a discussion about art because I don’t know much about it. Everyone’s different and if you don’t find science interesting, that’s OK.

But remember, the science you do at school isn’t the only science there is.

I bet you never find out why the sky is blue at school, or why your hands go wrinkly in the bath, or what shape wombat pooh is! Science is all around us and it’s fascinating.

I’ll go further and bet that, at school, they never taught you why clouds don’t float away, why apples are round and not square, how long it takes to get to the Sun in a bus, or what makes bags under your eyes. But the answers to all those questions, and 300 more, start here …

Happy digging.

Animal Magic

Talking dogs to purring tigers;clever cats to sleeping flies;blinking fish to baby turtles;yawning birds to rabbits’ tails

Why can’t dogs talk?

For a start, the shape of their mouths, their vocal chords and lack of a voice box are all wrong for making the sorts of sounds that humans make. We are exactly the opposite of dogs, we have long throats and small mouths and that’s why we can’t bark like dogs, or at least not in a way that a dog would recognise. There was once a famous dog on television in the UK who said ‘sausages’ – I know because I interviewed him! Have a look on YouTube – but he wasn’t really saying sausages; it was the way he growled that made it sound as if he was speaking.

Talking is far more than just making sounds. The forming of words and making words into phrases and then saying them calls for a lot of brain power, and dogs simply haven’t got it. Even so, dogs can ‘talk’ to each other in different ways and they’re cleverer at it than we are. We use words to communicate, and perhaps the looks on our faces too, but dogs employ their mouths, legs and tails, bare their teeth and position their ears to get their message across. Why would they need to talk as well?

Why do dogs bark at each other?

Wouldn’t it be wonderful if we really knew what dogs were trying to say to each other through their barks? What we do know is that dogs have many different types of bark – playful, nervous, excited, fearful, suspicious, stressed, even lonely. They also bark to protect their own territory and will only fight another dog if all else fails – they don’t like conflict. There are many barks from ‘ruff-ruff’ to growling to ‘yip-yip’ and once you get to know your dog, you start to get a hint of what it’s trying to communicate. You can be pretty certain that the first barks that two dogs exchange will be about territory – ‘get off my patch!’

Why don’t dogs sweat?

Sweat is the body’s way of trying to control its temperature and rid itself of some unwanted chemicals. When the body is overheated, special structures in the skin send a signal to the bit of your brain that controls temperature, which then sends signals to the sweat glands to produce sweat and transport it to the surface of the skin. Evaporation of the sweat cools the skin and the body temperature drops. That’s how it works for us. Animals such as dogs and cats only have sweat glands on the pads of their paws, which is not a large area. So, they have evolved to use panting as a way of controlling their temperatures by drawing cool air over their tongues. That is why you often see dogs with their tongues hanging out in hot weather. For some small animals, such as rats and mice, they cannot afford to lose water by sweating and so have no sweat glands at all.

Do dogs eat in the same way as humans?

Dogs do eat in exactly the same way as humans, contrary to appearances! The process of digestion starts when food is taken into the mouth, and is broken down both by the teeth and by saliva. The smaller particles of food then pass into the stomach where they are broken down by an assortment of chemical reactions. This is exactly the same for dogs as for humans. Dogs have larger canine teeth than we do, from having lived for a long period of their existence in the wild where they have had to hunt and kill for food with only their mouths as a weapon. They also have molars and pre-molars just as we do, and chew food to break it down, just like us. The only thing they haven’t quite managed yet are table manners.

What makes cats purr and dogs bark?

Let’s deal with cats first. This is a question to which there might be no proper answer, but lots of theories. One says purring is the vibration of ‘false’ vocal cords which are two folds of membrane behind the true cords, located in the larynx. Not all zoologists agree. Another theory suggests that purring is the direct result of turbulence in the bloodstream of the main vein returning blood to the heart from the body. This narrows in order to pass the liver and diaphragm, and the theory says that when the cat arches its back the blood forms eddies in this bottleneck. This in turn sets up vibrations in the chest which are amplified in the cavities of the skull.

It’s not true that cats only purr when they’re happy. Vets will tell you that cats purr while they’re having all kinds of uncomfortable treatments, even when in pain. Kittens start to purr at two days old, and the mother will purr back at them, so it might be some sort of communication. Some have suggested it is a kind of self-comforting sound which a cat can make to relax itself – a cat’s way of dealing with stress. It’s not only domestic cats who purr. Leopards can produce deep purring sounds, as can ocelots and pumas. Cats can purr while breathing in and breathing out, and can meow at the same time.

Dogs, on the other hand, are much more communicative than cats. A dog’s bark can carry far more messages than the simple purring and meowing of a cat. All this has developed over thousands of years to best suit the animal’s needs. Each animal communicates with others in the best way that it can. For a dog that means barking, for a cat the purr is better.

Which are more intelligent – cats or dogs?

There’s a big problem here – how can you ever work out how intelligent an animal is? For example, it’s easier to train a dog to fetch a stick than it is to train a cat, but does that make the dog more intelligent, or just more obedient? The other problem is that you are not comparing like with like. It’s as if you are asking ‘which is more intelligent – a dolphin or an orang-utan?’ They’re both very clever but in completely different ways. Most animals seem to solve problems by trial and error and not by thinking about them, although it’s possible that chimpanzees and some other primates do. But cats and dogs probably don’t, or if they do, only to a very limited extent.

As a general rule, animals are good at things that are natural for their own species, and bad at things that their species usually doesn’t do. So sheepdogs might be expected to be pretty good at problems concerned with rounding up sheep but other breeds of dog wouldn’t. And of course cats would be hopeless – they’re just not built for it! Which doesn’t answer the question, to which there is no real answer.

Why do cats sniff each other’s noses when they first meet?

They’re just being polite. In other words, it’s their way of saying, ‘Hello, how are you, where have you come from?’ It is cat communication. We shake hands, they rub noses. It’s possible they do it because of something in the saliva or on the breath that makes each cat unique. From this they can tell sex, maturity and possibly social status. So a good sniff is as good as a biography. Also remember that a cat’s close-up eyesight is not very good and so they have to rely on other signals to recognise other cats. But they don’t just rub noses. They sometimes sniff each other’s bottoms to get the same information. Incidentally, if your cat turns away and shows you its bottom, don’t be insulted – it’s simply trying to tell that at that particular moment you are the number one person in its life.

Why do cats have two eyelids?

They don’t – they have three. There’s a top and bottom eyelid, just like us, and then the third one. Dogs and rabbits also have them. It’s called a nictitating membrane. The eyelid has a tear gland on one side that helps keep the eye moist. This is the most important function of the eyelid, as the tears contain antibodies that help deal with infection. When cats fight they have a special mechanism that pulls the eye back a little way into its socket, and this allow the third eyelid to appear and provide added protection. If you want to see a cat’s third eyelid, look for it after your cat has just woken up from a long, deep sleep.

Can a tiger purr like my cat?

About 100 years ago an experiment was done in which scientists divided cats (large and small) into two groups depending on how bones and muscles at the base of their tongues were arranged. In one group of cats, the tongue and larynx were only loosely connected to the skull. In this group were tigers, lions, jaguars, leopards and snow leopards. These cats cannot purr, but they can roar. In the other group, which included the mountain lion and domestic cats, the arrangement of bones was slightly different and these cats can purr, but they cannot roar. Incidentally, the cats in the first group have round pupils in their eyes, and in the second the pupil is mostly a vertical slit.

My tabby cat has some hairs with different colours along their length. Why is this?

The colours in a cat’s fur are due to the presence of a pigment called melanin in the hairs. Melanin is usually black, although it can be converted to a chocolate brown colour. Sometimes, the hairs do not contain any pigment and then they are white. All cat coat patterns are made up of different combinations of these and other colours.

The pattern and colour of any cat’s coat depends on which colour pigment is produced and when, and this is controlled by the cat’s genes. In some cats, the hairs are the same colour along their entire length, but in other cats the colour of the hairs varies along the length. Sometimes the hair is yellow/brown for most of its length but with a black tip, or sometimes the hair has black bands all the way along it. This happens because the melanocytes (the cells which produce the pigments) produce different kinds of melanin at different stages in the hair’s growth.

Most mammals you see in the wild, such as brown rabbits or mice, have a flecked appearance which is good for camouflage.

My cat’s got fleas. My dog’s got fleas. Are they the same flea?

Bad luck. Cat fleas and dog fleas are actually different types of fleas. If you want to give them names they are Ctenocephalides felis and Ctenocephalides canis. However, there aren’t many fleas which only live on dogs; but there are far more cat fleas because cat fleas will quite happily live on any host they can find – which could be anything from a dog to a human being. Most fleas will feed and breed on a variety of hosts. An example of this is the cat flea which infects not only the domestic cat but dogs, foxes, mongooses, opossums, leopards, and other mammals, including man if nothing else is around.

Monkeys and apes do not get fleas, nor do horses. But fleas love rats, mice and squirrels because they tend to build their nests in holes which provide the right conditions for fleas to breed. Fleas feed on blood, but can survive for a long time without food. The rabbit flea, for example, can live for nine months at temperatures around the freezing point without feeding.

Can tarantulas change sex?

When tarantulas are young they all look like females, but as they get older their sex becomes more obvious. Adult males have hooks on their front legs and their stomachs, and are smaller than females. The males’ ‘pedipalps’ (the feely bits that stick out of the head) are shaped like clubs. It may take ten moults – seven years – for these differences to become obvious. So, it might look as though tarantulas change sex when they moult; but they don’t, it’s just that the differences between males and females become more obvious.

How far can ants see?

Some worker ants have well-developed eyes and can leap from branch to branch. Some have tiny eyes, and worker army ants, which are the most aggressive ants in the world, will eat anything that gets in their way even though they are blind. They use their antennae for smell and touch but they have no eyes at all. However, the jumping ants of India, unlike most ants, can jump to catch prey and have two large eyes to help them navigate. But the picture their eyes provide is not like the one we would see. Ants’ eyes are ‘compounded’ so, instead of seeing one big picture, it would be more like looking at a shop window full of television sets all showing the same picture.

How strong is an ant?

Ants can carry up to fifty times their own body weight on their back, and their pincers can grip something 1,400 times their weight. The reason they can lift things many times their body weight is all down to simple physics. Their muscles are no stronger than human muscles but, because they have a very small body mass the proportion of their mass that is muscle is very high. With elephants it’s the reverse – the proportion of their mass that is muscle is low so they can’t lift their own body weight. If we were as small as ants, we’d be able to lift weights like they do.

By the way, some ants can be pretty aggressive. Army ants are called ‘swarm feeders’ and hunt just like an army. They eat lizards, snakes, goats, scorpions and beetles, and an army of them can consume 100,000 creatures a day!

Why don’t flies knock themselves out when they fly into windows?

Basically, houseflies don’t have enough momentum to stun themselves. If they flew faster they might – we all know what happens to a fly when it hits the windscreen of a car travelling at speed. Or if they were heavier they might – some heavier beetles like cockchafers and stag beetles can stun themselves by flying into windows.

Where do flies go in winter?

Flies, like all other insects, are cold-blooded so they can’t regulate their temperature internally. When warm-blooded creatures, such as ourselves, get cold we can warm ourselves up to some extent by shivering. When cold-blooded creatures get cold they can’t warm themselves up so they can’t actually do much about it. Insects, including flies, can cope with the cold winter in three different ways. They can try and muddle through as best they can, and this is what some of the smaller species of fly do. Others hibernate, and emerge in the spring when the weather gets warmer. However, the vast majority of flies lay eggs and then die. The eggs sit quietly in a corner until the spring when they hatch and produce a new generation of flies.

Where does the bluebottle fly sleep at night?

Like most insects they don’t go to sleep in the sense that we do, but they do take a rest. Their breathing and heart rate slows and so they use less energy. They don’t close their eyes like we do, because they don’t have eyelids. Even though they are resting they still have to remain on alert because predators are everywhere, waiting to pounce. As far as bluebottles are concerned, like flies, they don’t sleep but simply take a pause from buzzing around and start again as soon as the sun comes up.

Why do flies whizz around the light bulb, even when the light is off?

No one’s really sure why they fly around the light bulb. Some say it’s because it’s the middle of the room and flies don’t like corners. Another theory says they tend to stay in the middle of the room searching for a perch as it is the best position to fight off a rival or for attracting a mate. Male flies tend to establish a ‘lek-type mating assembly’ around ceiling lights – that’s when they get together and display themselves to attract females. Female houseflies that are aiming to perch on the light fitting are intercepted by any male lucky enough to be patrolling the airspace closest by. Males therefore compete to occupy the top position, and will chase out any other flies which are threatening to invade their airspace. The next time that you see a housefly circling purposefully beneath one of your ceiling lights, try throwing a fake fly at it – a bit of fly-sized paper will do. The fly will almost certainly break from its horizontal circling to chase the ‘intruder’ away.

Why do snails only come out at night?

Actually, they will come out at any time of day, it’s just that they prefer the darkness. Snails have a moist surface to their bodies which allows water to pass inwards or outwards very easily. If they spent too long in the sunshine it is quite likely they could become dehydrated by evaporation, so they aren’t out and about as much in broad daylight.

How many eyes does an earthworm have?

The simple answer to this is that they have none. Earthworms are very basic creatures. They have no eyes or ears. However, their entire body, particularly the upper surface, is incredibly sensitive, especially to light. They can also sense vibration and will easily detect the movement of a mole – earthworms will quickly rise to the surface if they sense one is digging close to them. However, they won’t stay on the surface long, because if exposed to too much light they become paralysed. What makes them so sensitive is that they have a nervous system which runs the entire length of their body. They don’t have brains, but they do have a large collection of nerves which bundle together in the head region of a worm.

Did you know that in one acre of land there can be as many as a million worms?

If you cut a worm in half, will it live?

It will depend where the cut is, and which bit of the worm you’re talking about. The bit with the head in it might well survive and it could attempt to grow a new tail, but the bit without a head would certainly die. In order to repair itself, the front part of the worm must contain the clitellum – a kind of gland which looks a bit like a saddle – and about ten segments after that. Any shorter and your worm will die. Not all worms can perform this trick, so it would also depend on which type of worm you are talking about.

Can fish see in the dark?

A fish eye has a very large pupil which allows a lot of light into the eye, so fish can see in much darker conditions than we can. But to be able to see there has to be some light. Some fish live very deep down in the dark ocean in what we call the ‘twilight zone’, and at these depths they can employ organs called photophores which give off light and can be arranged in lines or patterns across the fish’s body. They can use these photophores as a sort of searchlight, or for dazzling other fish and attracting food.

Do fish blink?

No, they don’t have moveable eyelids but they do have one transparent eye protector over their eyes all the time. They don’t have a problem with keeping eye tissues moist – there’s plenty of moisture around – but like all eyes they need protecting from sharp objects and dirt. Fish eyes are actually quite amazing. They have excellent eyesight and can see parts of the spectrum we can’t, like UV (ultraviolet). Some can also distinguish polarised light, which can improve contrast so that other fish might become more visible.

How do you measure the memory of goldfish?

One way of testing the memory of a goldfish is with an underwater maze which has food at the end. Once the goldfish has learned its way through the maze you can wait and see how long it takes for the fish to forget. An alternative is a test where fish are presented with two boxes, only one of which has food in. The fish can be trained to learn which of the boxes contains the food and, again, you can wait to see how long the fish remembers this. There’s a myth that goldfish only have a three-second memory – some scientists say it’s as long as twenty-four hours, others think it might be as long as five months.

Do fish have hearts?

Fish do have a heart but it only has two chambers, unlike our heart which has four. This is because the fish heart only pumps blood around the body, whereas our heart has to pump blood around the body and also around the lungs. Fish don’t have lungs because they get oxygen from the water around them, using their gills. In a fish, the blood enters the heart through a vein and exits through a vein on its way to the gills. In the gills, the blood picks up oxygen from the surrounding water and leaves the gills in arteries, which go to the rest of the body. The oxygen is used in the body and the blood goes back to the heart.

Why do fish have scales?

Scales are small overlapping bony plates which provide greater protection for the fish. They are a kind of exoskeleton, like the shell of a crab. It’s like body armour.

Do fish sweat?

Mammals which live surrounded by air, cool themselves by evaporating moisture from their skin. Fish have no such means of maintaining a constant body temperature, and their blood is usually at the same temperature as their surroundings, which is the water they’re in. So, fish have no need to sweat. Most fish will die if the water becomes too hot or too cold, or changes temperature too suddenly. This is why care is needed when transferring fish into a new aquarium so that they have sufficient time to adapt to the temperature of their new surroundings.

Can fish love each other?

I suppose you’re asking if fish have emotions. It’s impossible for us to tell how a fish feels about anything, but there was once an interesting experiment: a female fish, ready to mate, was put in a tank with two males. She formed an association with one of them. Let’s call it love. The two males then started to fight over her and scientists studied her brain responses while she watched them. Certain parts of her brain became highly active at moments when her boyfriend was taking a beating. What does that tell you? It certainly doesn’t prove love between them; you can’t simply translate brain activity into feelings. But that experiment comes under the heading of ‘very interesting’…

Why don’t whales get the bends?

Let’s be clear about what ‘the bends’ are. When people dive deep into the sea they wear a diving tank and are breathing air at higher pressures than normal, which means pressure is built up in the body. If they change their external pressure too quickly, by suddenly rising to the surface for example, then the absorbed gas is released too quickly in the form of bubbles throughout the body. It’s also called ‘compression sickness’ and gives rise to painful joints, paralysis and possible death – that’s in humans.

Whales, however, take a breath while on the surface and before they dive, and don’t breathe again while they’re underwater, so they’re not taking in any pressurised air. In fact, whales can breathe out as they dive and collapse their lungs in order to fill their blood with as much oxygen as possible. That’s why the bends is not a problem for them.

Is whale poo huge?

Whale faeces (or ‘poo’ to you and me) will contain undigested materials like fish eyes and squid beaks, depending on what the whale’s been eating. Whales are mammals and, just like any other mammals, their digestive system will produce waste organic materials. It is difficult to describe exactly what form this takes because it’s shed directly into the sea and breaks down, but generally speaking it will tend to be in liquid form. Sometimes, though, it can float for a while and then sink while dissolving in the water.

Why can’t whales move when they are beached?

Whales swim by moving their tails, or ‘flukes’ as they are more accurately known. Upthrust is important for anything floating in water. Unless you have an upthrust equal to the force downwards, you will not float. Upthrust is created by displacement. As you push the water out of the way, the water pushes back and this is what makes you float. As whales are so large, when they beach their bodies can’t support themselves without the help of the upthrust and so they become helpless.

How do turtles breathe underwater?

Turtles don’t always need to breathe underwater. Sea turtles can hold their breath for up to five hours, and could spend that long submerged. They’re also cold-blooded creatures and have a slow metabolism so don’t have the same urgent need for oxygen as we do. If they’re swimming hard they may come up and take a breath much more often; if they’re resting then they can hold their breath for hours.

How do baby turtles find their way to the sea?

Their mothers don’t help them, because once they have laid their eggs they return to the sea, so the newborn turtles follow the daylight instead. The sea is usually brighter than the land, and even at night it reflects some light, so the little turtles use that to guide them. In fact, they prefer to make the journey at night because it makes it more difficult for predators to spot them. Even more remarkable is the fact that once they have found the ocean, they can then swim for 5,000 miles and still find their way home. No one knows how they do it. It’s such a risky thing, being a baby turtle, that only one in a thousand will survive to become fully grown.

How long do sharks live?

The great white shark becomes mature when it reaches 11–14ft, and by the age of 14 it will reach 16ft. After this, they can reach ages of up to 40 years, although some say it could be as much as 100 years. Smaller sharks might live for twenty to forty years. The truth is we know very little about the lifespan of sharks.

Can male seahorses have babies?

Yes, they can. What happens is that the females lay their eggs in their partners’ pouches, so it is the males that eventually carry the offspring. They do this for three weeks, and go through about seventy-two hours of labour before the baby seahorses emerge – there might be as many as 200 of them. A lot of people think that seahorses only exist in stories, but they are real enough. They may have evolved at least 40 million years ago, and have changed very little since.

Is it true that a bird eats bits out of alligators’ teeth?

It might be a bit of a tall story, but there again it might just be true. The Egyptian plover and the spur-winged plover are most likely to be the brave ones who perform this trick, because they both feed close to basking crocodiles. The common sandpiper also feeds near crocodiles in Africa during the northern winter. All three of these bird species are ‘waders’, or shorebirds, and are very brave!

How strong is a crocodile’s bite?

The muscles that close a crocodile’s jaws are very strong. They crush turtle shells with ease, and a large saltwater crocodile holding a pig’s head can simply crush the skull by flexing the muscles from a standing start. But the muscles involved in opening the jaws have little strength. A rubber band around the snout is enough to prevent a 2m-long crocodile from opening its mouth.

Can Crocodiles Cry?

Have you heard an expression called ‘crying crocodile tears’? It means when someone cries but the sadness is not genuine. For example, the school rings up and says the exams have been cancelled and you burst into tears. In fact, you’re over the moon, but you want everyone to think you’re disappointed. Those are called ‘crocodile tears’.

There’s a difference between producing tears, which is a physical response, and real crying, which is an emotional response. In the case of crocodiles, they can produce tears from lachrymal glands pretty similar to our own, and these tears are used to lubricate the front of the eye. Crocodiles don’t cry because they’re sad, like we do, although the legend goes that crocodiles produce tears in order to lure prey. It’s a myth, and it goes all the way back to the thirteenth century when a monk wrote, ‘If the crocodile findeth a man by the brim of the water … he slayeth him there if he may, and then weepeth upon him.’ If you were to watch a crocodile closely while it was eating its prey, it might look as if it were crying. This may be because the huge force that comes into play when a crocodile bites down hard, squeezes the tear ducts and creates a weeping effect.

Why has the crocodile survived, but the dinosaur didn’t?