The 6 simple machines

http://je012.k12.sd.us/3rd%20grade/Simple%20Machines.htm

There are 6 simple machines:  Inclined Plane, Wedge, Screw, Lever, Wheel and Axle, and Pulley.

A machine is a tool used to make work easier. Simple machines are simple tools used to make work easier. Compound machines have two or more simple machines working together to make work easier. In science, work is defined as a force acting on an object to move it across a distance. Pushing, pulling, and lifting are common forms of work. Furniture movers do work when they move boxes. Gardeners do work when they pull weeds. Children do work when they go up and down on a see-saw. Machines make their work easier. The furniture movers use a ramp to slide boxes into a truck. The gardeners use a hand shovel to help break through the weeds. The children use a see-saw to go up and down. The ramp, the shovel, and the see-saw are simple machines.
	Inclined Plane A plane is a flat surface. For example, a smooth board is a plane. Now, if the plane is lying flat on the ground, it isn’t likely to help you do work. However, when that plane is inclined, or slanted, it can help you move objects across distances. And, that’s work! A common inclined plane is a ramp. Lifting a heavy box onto a loading dock is much easier if you slide the box up a ramp—a simple machine. Want to know more? Here’s extra information.
	Wedge Instead of using the smooth side of the inclined plane, you can also use the pointed edges to do other kinds of work. For example, you can use the edge to push things apart. Then, the inclined plane is a wedge. So, a wedge is actually a kind of inclined plane. An axeblade is a wedge. Think of the edge of the blade. It’s the edge of a smooth slanted surface. That’s a wedge! Want to know more? Here’s extra information.
	Screw Now, take an inclined plane and wrap it around a cylinder. Its sharp edge becomes another simple tool: the screw. Put a metal screw beside a ramp and it’s kind of hard to see the similarities, but the screw is actually just another kind of inclined plane. Try this demonstration to help you visualize. How does the screw help you do work? Every turn of a metal screw helps you move a piece of metal through a wooden space. And, that’s how we build things! Want to know more? Here’s extra information
	Lever Try pulling a really stubborn weed out of the ground. You know, a deep, persistent weed that seems to have taken over your flowerbed. Using just your bare hands, it might be difficult or even painful. With a tool, like a hand shovel, however, you should win the battle. Any tool that pries something loose is a lever. A lever is an arm that “pivots” (or turns) against a “fulcrum” (or point). Think of the claw end of a hammer that you use to pry nails loose. It’s a lever. It’s a curved arm that rests against a point on a surface. As you rotate the curved arm, it pries the nail loose from the surface. And that’s hard work!
	Wheel and Axle The rotation of the lever against a point pries objects loose. That rotation motion can also do other kinds of work. Another kind of lever, the wheel and axle, moves objects across distances. The wheel, the round end, turns the axle, the cylindrical post, causing movement. On a wagon, for example, the bucket rests on top of the axle. As the wheel rotates the axle, the wagon moves. Now, place your pet dog in the bucket, and you can easily move him around the yard. On a truck, for example, the cargo hold rests on top of several axles. As the wheels rotate the axles, the truck moves.
	Pulley Instead of an axle, the wheel could also rotate a rope or cord. This variation of the wheel and axle is the pulley. In a pulley, a cord wraps around a wheel. As the wheel rotates, the cord moves in either direction. Now, attach a hook to the cord, and you can use the wheel’s rotation to raise and lower objects. On a flagpole, for example, a rope is attached to a pulley. On the rope, there are usually two hooks. The cord rotates around the pulley and lowers the hooks where you can attach the flag. Then, rotate the cord and the flag raises high on the pole.
If two or more simple machines work together as one, they form a compound machine. Most of the machines we use today are compound machines, created by combining several simple machines. Can you think of creative ways to combine simple machines to make work easier? Think about it.

Hair

Everyone seems to know the basics, hair is made of dead cells. Beyond that we only know to shampoo it, comb it and try to prevent split ends. So how exactly is this hair formed when we have plenty of other dead cells falling off our skin all the time?

The key is a substance called keratin. When the cells die it leaves a cylinder of keratin, an extremely strong protein. So strong in fact, that the only biological material stronger than keratin is chitin.  Now before you go bragging about how strong your keratin is to all those bald friends you need to know that their are types of keratin. It just happens to be that the keratin that makes up the hair on your head is not near as tough as that which makes up the claws and scales of reptiles. 

So yes, their keratins could beat up your keratins.

While completely lifeless, hair does contain minerals, fats, and water (10%). So, if you are ever on a deserted island you could survive just a little longer on a nice fistful of hair. However, growing on average 1 cm a month means this food supply isn’t very replenishable. Eat wisely.

Dirt

Where would we be without dirt?

Honestly, the economy depends on dirt. If we didn’t have dirt it would put the entire cleaning industry out of business, the economy would collapse, and you’ll be out on the street waiting for a street-sweeper that would never need to come. Count your lucky stars that dirt’s got a long-term contract and isn’t cleaning up it’s act anytime soon. 

Dirt (soil) forms the pedospherem, which is a nice Latin name for the grubby interface between the lithosphere (rocky part of the planet) and the biosphere, atmosphere, and hydrosphere.

Dirt is a three phase system comprised of all kinds of little bits, from rocks and minerals, organic matter (including all sorts of living organisms), ice, weathered rock and precipitates, liquid water solutions, and gases (worm farts).

The ‘liquid phase’ is primarily water, and is also known as the ‘soil solution’ where plants get their nutrients. The ‘gaseous phase’ is important for supplying oxygen to plant roots for respiration. Fortunately, there is no ‘teenager phase’.

Soil formation, or pedogenesis, (use that in a sentence some time this week) is the combined effect of physical, chemical, biological, and anthropogenic processes on big things turning them into progressively littler things which you want to keep out of the corners of your bathroom.

Oh yeah, we’re all going to become dirt in the end so show some respect. 

The Butterfly Effect

Can a butterfly flapping it’s wings can cause a hurricane?

Well, maybe. Really complex systems like the weather and ecosystems are pretty, well, complex. (How my wife drives is also a complex system but so far has resisted any scientific understanding.)

The butterfly effect is simply this: Any change in the initial conditions of a complex non-linear system creates wildly different outcomes.

A more technical description would be: sensitive dependence on initial conditions in chaos theory where small variations of the initial condition of a nonlinear dynamical system produce increasingly large variations in the long term behavior of the system. Whew.

The phrase The Butterfly Effect refers to the idea that the single flap of a butterfly’s wings change the initial conditions of the system enough to cause large-scale phenomena (hurricanes and such) since any variation in the initial conditions is vastly magnified with each iteration. And every flap of every butterfly wing in the world continually changes those conditions. (Someone passing gas in France probably caused the Katrina hurricane.) Now you know why you don’t want to be a weatherman. It basically means that we’ll never be able to predict the weather for more than a few days.

 

See that equation? Looks tricky doesn’t it? You can’t understand how my wife drives either.

Comparing the butterfly effect to the domino effect is slightly misleading. In the domino effect there is dependence on the initial sensitivity, but whereas a simple linear row of dominoes would cause one event to initiate another similar one, the butterfly effect amplifies the condition upon each iteration. Also, dominos are a game played by old people in Miami.

Animal populations can be subject to the same phenomena.

Predator-prey systems have complex dynamics. A bio system with two variables such as rabbits and foxes can create a system that is much more complex than is readily apparent. Lack of foxes means that the rabbit population can increase, but increasing numbers of rabbits means foxes have more food and are likely to survive and reproduce, which in turn decreases the number of rabbits.

So please, don’t pass gas. Forecasting the weather is hard enough.

Why Evolution is a fact, but how it works is a theory.

Evolution is a fact. How evolution works is a theory.

“In the American vernacular, ‘theory’ often means ‘imperfect fact’—part of a hierarchy of confidence running downhill from fact to theory to hypothesis to guess. Thus the power of the argument: evolution is ‘only’ a theory and intense debate now rages about many aspects of the theory.

If evolution is less than fact and scientists can’t even make up their minds about the theory, then what confidence can we have in it?

Well evolution is a theory. It is also a fact. And facts and theories are different things, not rungs in a hierarchy of increasing certainty. Facts are the world’s data. Theories are structures of ideas that explain and interpret facts. Facts don’t go away when scientists debate rival theories to explain them. Einstein’s theory of gravitation replaced Newton’s in this century, but apples didn’t suspend themselves in midair, pending the outcome.”

- Stephen J. Gould, ” Evolution as Fact and Theory”; Discover, May 1981

Let’s consider evolution in light of another scientific fact - gravity. Gravity is also fact. How gravity works is a theory. Current theories about gravity might be disproved, but gravity itself remains a fact. 

A number of terms have been attached to Darwin’s theory although they are commonly misunderstood.

Survival of the fittest does not mean survival of the strongest, smartest, fastest or best camouflaged. Survival of the fittest means that an organism that is best adapted to its ecological niche is more likely to create more offspring than less fit individuals. Consider the garden slug as an great example of fitness for survival.

Natural selection is Darwin’s theory of how the environment works on species. Individuals that are most successfully reproducing viable offspring form the core gene pool of a species. Environmental forces determine which individuals survive.

The evidence for Darwin’s theory of evolution grows more unimpeachable as science discovers more about chemistry, geology, and biology.

Take a look at your dog. He’s a perfect display of the mechanisms of evolution. If he’s anything other than a 30 pound dingo looking mutt, the gene’s he displays that make him a cock-a-poo, German Shepard, or Bouvier (my favorite) were selected from an existing gene pool by humans to make him what he is. While all dogs are the same species and a great dane can breed (theoretically) with a chiwawah, you get the idea. His genes have been modified over time to make him different than he was.

So, The Theory of Evolution does not describe evolution as a supposition. It is the the current thinking about how the fact of evolution manifests itself.

Why the Sky is Blue?

If you’ve got kids, and I do, you can impress their little minds by having savvy answers ready for  the questions they answer while they’re examining their navels.

Why is the sky blue? Why doesn’t the sky just stay black with the sun acting as another point of light? Why do the stars disappear during the day?

Got your long-term memory ready? Here’s the answer. The first thing to understand is that the sun is slightly brighter than the moon and stars. You can verify this by staring at the sun and burning your retinas out in a minute or so. (Staring at the moon is doesn’t do this and is actually romantic.) Also of note is that the atmosphere (nitrogen and oxygen molecules) has an effect on the happy little sun beams passing betwixt them.

There is a physical phenomenon called Rayleigh scattering that causes light to scatter when passing through molecules that have a diameter one-tenth that of the wavelength (color) of the light.

Sunlight is made up of all different colors of light, but because of the physical properties of all those oxygen and nitrogen molecules in the atmosphere, blue wavelengths of light are scattered much more efficiently than the other colors. So while most wavelengths hitting the upper atmosphere just pass through and on into space, blue lights path get changed, resulting in a defuse blue light coming from all directions of the atmosphere.

So when you look at the sky on a clear day, you can see the sun as a bright disk surrounded by blue as the atoms in the atmosphere scatter the blue light waves toward you. Got that?

Of course the sky on Mars is not blue. (See the color pictures from Mars Pathfinder) This is because the atmosphere of Mars is very thin and dusty, and atmospheric light scattering is dominated not by Martian atmosphere (mostly carbon dioxide) but by suspended dust particles. These are larger than the wavelengths of visible light, and they are reddened by iron oxide from the Martian soil. It’s not just Rayleigh scattering, so the spectrum is different.

Now when you kids ask you why the sky is blue, you can dazzle them with the explanation above, or you can say that it’s blue because that’s your favorite color. It works just as well and will probably impress your kids even more.

More on the blue sky and scattering 

Micro-organisims & You

While you might be close to your friends and family, but you have friends who are closer still. 600 different species of bacteria inhabit your mouth every morning. They’re the little guys that make up that tasty film on your teeth. Yum.

And it doesn’t stop there. About 500 species of bacteria, as well as many species of yeast and other organisms, inhabit your human gastrointestinal tract and make up your “gut flora”.

Yep. You’re a veritable Petri dish of little goo-critters. If you’re an ‘average’ human, the bacteria weigh in at about 1kg and the number of individual micro-organisms easily outnumbers the total number of cells in your bug-loving human body. (So far, none of these organisms have been identified as the midicloreans that Yoda uses to channel The Force but perhaps if you don’t brush your teeth you’ll have a nagging desire to build a light saber.)

Luckily for us a large number of these organisms don’t cause disease — instead, they help protect us from disease. The gut flora perform many functions that contribute to the health of the human host; “friendly bacteria” mostly have names beginning with Lactobacillus or Bifidobacteria.

The friendly bacteria aren’t the only type of microorganism present in your gastrointestinal tract however. There are also a number of organisms that don’t provide you with any benefits; these include coliform bacteria, yeasts and bacteroides.

Motion Sickness

Motion Sickness: My idea of the seventh level of hell is being stuck in winter ski-gear, in between two fat guys on a bus, in sunny weather, driving in circles searching for a parking space, backwards.

If you’re not currently puking your guts out and feeling woozy, it’s because your eyes, inner ears, skin, and muscles are sending signals to your brain about your bodies current position in space and tracking the direction of movement of all of your various parts. And all the signals are saying the same thing. That’s good.

If that’s not what’s happening and your ears, eyes and such are sending conflicting information and arguing about what’s going on with your body, that’s bad, and stand back because I don’t want you splashing anything nosesome on my shoes.

Motion sickness is that most noxious of feelings that happens to you when your balancing system gets overwhelmed by contradictory messages sent from the eyes and inner ears. Stuff like sweating, light-headedness, hyperventilation, nausea, vomiting and a remarkable ability to let loose incredible profanity without moving your head. If your eyes are telling you one thing, and the fluid of your inner ears are sloshing around telling you another, your brain seems to make a command decision and put everyone in time out.

For some people, motion sickness can be brought on merely by walking down the aisles in a supermarket or watching telephone poles whipping by a car window. Some people can even get motion sickness sitting in a theater and watching an action-packed film on one of those super-sized movie screens. Lets just hope that they’re not sitting right behind you.

Motion sickness in space is very common. Evidently your brain just won’t believe your ears that gravity’s been suspended for a while, and the Space Shuttle comes equipped with numerous barf ports. This is a good thing since who want’s to see that floating around in zero g.

What can you do to prevent motion sickness?

There are a number of options, home remedies, and hope. (There’s always hope.) By far the best option is to have your doctor prescribe a drug like Scopace (Scopolamine) which is an anticholinergic central-nervous system depressant. That’s good since it’s your anticholinergic central nervous system that’s trying to kill you. You want it depressed.

Locusts

Locusts are part of a large group of insects commonly called grasshoppers which have big hind legs for jumping. (Kangaroos also have big hind legs for jumping but are not part of this group.)

Locusts belong to the family called Acrididae but differ from grasshoppers in that they have the ability to change their behaviour and habits. So, while locusts could stop smoking if they want, grasshoppers are paying big tobacco ‘till they go legs up.

A Desert Locust lives a total of about three to five months although this is extremely variable and depends mostly on weather and ecological conditions. Their little life cycle has three stages: egg, hopper and adult. Eggs hatch in about two weeks, hoppers develop in five to six stages over a period of about 30-40 days, and adults usually mature in about two to four months (Sometimes as long as nine months for late bloomers or locusts that are still living with their parents).

Locust swarms can vary from less than one square kilometre to several hundred square kilometres. There can be as many as 80 million locust adults in each square kilometre of swarm which means they can’t remember everyone’s name and are constantly saying ‘excuse me’ as they bump into each other.

One Desert Locust adult can consume roughly its own weight (about two grams) in food per day. You on the other hand take a year to eat your own body weight if you’re average. I take about six months.

Each ton of locusts eats the same amount of food in one day as about 10 elephants or 25 camels or 2,500 people. A large swarm can in a cultivated area can eat enough food to feed 400,000 people for one year. You can see why people complain.

In order to get back at locusts, sometimes people eat them. If you ever find yourself in the middle of a swarm, take advantage.

Here are some recipes to help.

Boiled Locust: remove the wings and hind legs of the locusts, and boil in a little water until soft. Add salt, if desired, and a little fat and fry until brown. Serve with cooked corn.

Roasted Locust: prepare embers and roast the whole locust on the embers. Remove head, wings, and legs. Only the breast part is eaten.

Traveling Locust: If traveling do what the South Sotho people do. The heads and last joint of the hind legs are broken off and the rest laid on the coals to roast. The roasted locusts are ground on a grinding stone to a fine powder. This powder can be kept for long periods of time and is taken along on a journey. Dried legs are especially relished for their pleasant taste.

Cambodian Peanut Stuffed Locust: take several dozen locust adults, preferably females, slit the abdomen lengthwise and stuff a peanut inside. Then lightly grill the locusts in a wok or hot frying pan, adding a little oil and salt to taste. Be careful not to overcook or burn them.

Grilled Locust: prepare the embers or charcoal. Place about one dozen locusts on a skewer, stabbing each through the centre of the abdomen. If you only want to eat the abdomen, then you may want to take off the legs or wings either before or after cooking. Several skewers of locusts may be required for each person. Place the skewers above the hot embers and grill while turning continuously to avoid burning the locusts until they become golden brown.

Why time slows down when approaching the Speed of Light.

Ok, so you’ve heard that nothing can travel faster than the speed of light. (That’s not quite true. The expansion of the universe allows for faster than light travel but that’s another post.) You’re also aware that time slows down the closer you get to the speed of light. You know, the ‘One twin goes off to Alpha Centauri at the speed of light and comes back after 80,000 years but he’s only aged 3 months’ story.

Ever wonder why? Here’s the crib notes.

Everything in the universe always travels exactly at Light Speed. Always.

spacetime.gif

Time dilation: Special relativity declares a law for all motion: The combined speed of any object’s motion through space and it’s motion though time is always precisely equal to the speed of light.

That’s right, everything. You, me, the computer screen you’re looking at, your grandma’s French toast, Santa Clause… everything.

Everything is traveling through Spacetime: space (the three dimensions we experience and the nine others that m-theory predicts) and time.

Adding the total movement through both space and time always equals light speed. Always. Always. Always.

Space and Time do not exist seperately, the are parts of the same thing, Spacetime.

Since you must travel constantly at exactly the speed of light, when you increase your speed through space, you decrease your speed through time.

Your head (and the rest of you) is traveling through spacetime at the speed of light. But, when you’re at rest (not accelerating) all of your head’s movement is through time, none of it is traveling (accelerating) through space. Every time your head moves (accelerates) through space; in a car, in a plane, in a spaceship… even nodding up and down, some of it’s movement in time is lost since it is now moving through space.

Cool huh.

What about light?

Since light waves use all of their motion to travel through space at Light Speed, they have absolutely no motion through Time. Every photon that has ever been produced exists in an ageless state. (To us, the light seems to move through time but to the photon, time is standing still. This is one of the seemingly odd realizations fo Ensteins Theory of Relativity.) That's why poton's from the early universe don't 'fade out' or do something else. They can't, since for them, time is at a standstill.

The universe ages, light does not.

Reading: The Fabric of the Cosmos: Brian Greene

Blood

Ok, here’s the deal on your blood. As an average adult, you have about five liters of blood flowing through your veins. The entire volume is made up of four components; red blood cells, white blood cells, platelets, and plasma.

Red blood cells are red. They’re the little guys that do the heavy lifting by carrying oxygen around your body. They’re kind of like college students who are moonlinght as movers. Normally, these little guys are shaped kind of like a doughnut without the hole in the middle going all the way through. (More like a depression than a hole really.) However, these guys can change their shape in order to move through tiny capillaries. In addition delivering oxygen, red blood cells pick up carbon dioxide, a waste product of cellular respiration and the stuff you don’t want anymore. This is handy as it would be a waste of a trip if you had to have someone else come get this carbon dioxide and the red cells are right there anyway. When red cells are carrying oxygen they are bright red but deoxygenated blood (not carrying oxygen) is a really dark maroon color giving veins their ‘blue’ coloring.

Half your body’s red blood cells are replaced every seven days which is easy to understand when you realize that iIf all the blood vessels in your body were laid end to end, they would reach about 60,000 miles.

White blood cells are the gunslingers of the blood posse. They go around nuking, spraying, and slurping up all the little critters that you don’t want around like bacteria and viruses. The most common white blood cells are neutrophils and lymphocytes. Neutrophils are kind of like ‘the Blob’ and literally swallow their enemies alive through a process called phagocytosis (cell eating) which is really unpleasant if you’re the one getting absorbed. Lymphocytes are a lot smarter. They adapt their shape to destroy new viruses and bacteria that enter the body. While this time for previously unknown pathogens, your lymphocytes remember all their past encounters which prevents you from getting sick from the same illness in the future. (It’s good to know that every flu you catch is a different one. Vive le difference.)

Platelets are not very smart. They don’t have to be since their job is simply to find a breech in a vessel wall and throw themselves into it. They’re the ones who begin to form a clot when you cut your finger, kind of the Kamikaze of the blood system.

Red cells, white cells, and platelets are all formed in your bone marrow from the same stem cells.

Plasma is the fluid that carries all these cells around. It’s 90% water with a 10% smattering of proteins, electrolytes, glucose, vitamins, hormones, and cholesterol. (As far as I know there’s no salt and pepper.)

Addition Facts:

• On average, men have 5.2 million red blood cells per cubic millimeter while women have 4.6 million.

• Jewish dietary laws do not allow blood to be consumed in any way. Traditionally, salting and pickling purges blood from meat.

• According to Chinese folklore, nosebleeds are a sign of sexual arousal in men

The Placebo Effect

The Placebo Effect is the influence of a treatment that has no medical value but seems to have a beneficial effect. (Kind of like apologizing to your wife for something you didn’t do.)

Inject a close-to-celestial-discharge patient with salt water and give him a sugar pill, and for some reason, he’ s back up and running in no time. This is especially true for subjectively assessed disorders such as migranes, back pain, and depression, which are all just in your head anyway. The placebo effect may account for a large part of the therapeutic value we subscribe to medications which is good news for those medications that don’t really work that well, since at least you think they do.

(There’s a sneaking suspicion that that erectile dysfunction ad that tells you to seek a doctor if you have an erection lasting more than four hours is an attempt at giving you a big setup.) 

The placebo effect for pain medications has been at least partially explained by brain chemistry. When the brain experiences pain, it releases endorphins—chemicals that naturally act like morphine to relieve pain and make you really, really happy. Brain imaging studies have shown that when a person takes a placebo, it triggers the release of endorphins. Neurologically, it’s as if he had taken the illegal drug, but without the trouble of having to do shady deals through his car window.

There is also the less understood but equally powerful nocebo effect. Often, people who are told that they are going to experience negative side effects from a drug do, even if there is no medical reason for it. In one study, people were given a sugar pill and told that it induced vomiting. Later, 80% of them started throwing up, which is why it’s such great fun to be a janitor at nocebo testing clinics.

Similarly, in another study, women who believed they were going to die of a heart attack were found to be four times more likely to die of a hart attack than women with the exact same medical profile who did not think that they were at risk. Thinking sick may make actually make you sick which makes it quite possible that Richard Simmons will live forever.

In some areas of medical treatment, the placebo effect actually seems to be getting bigger. In studies of aintidepressants, the response rate to placebos has been increasing by 7% every ten years. In 1980, 30% of depressed people given a placebo improved without any other treatment; in 2000, it was 44%. This may be due to widespread advertising and heightened expectations for drugs. In general, the public has more faith in psychiatric medications than it did twenty year ago, which give placebos more power.

Additional Facts:

• The color of the pills may also have an effect on some patients. In one Italian study, blue placebos made excellent sleeping pills for women and had the opposite effect on men. (Perhaps because it looked like Viagra and perhaps just because they were Italian.)
  

• Painful injections may have more therapeutic value than ones that hurt less so remember to ask the physician for a really painful one.
  

Why do we have baby teeth?

Image from iStock Photo

“Baby teeth (also known as deciduous or milk teeth or nipple nashers) are widely found in the animal kingdom.

While fish and reptiles continuously renew their teeth and go through many generations of them in a lifetime, mammals have followed an evolutionary trend toward suppression of tooth replacement since we love our teeth more than fish love theirs.

The reason is not known, but because the cusp pattern on mammalian teeth leads to complex patterns of occlusion (that is, the way the upper and lower teeth fit together = biting), it’s likely that subtle differences in tooth shape that might occur with frequent tooth replacement could lead to malocclusion, a dangerous situation where food couldn’t be chewed properly and you talk funny which would make mammals look more ridiculous than we already are. It could increase cavities as well so it may be that mammals will do just about anything to avoid going to the dentist.

In humans and other mammals, development has been restricted to just two sets of teeth. Young mammals’ skulls are small, and it’s impossible for them to accommodate a full array of adult choppers so juveniles have cute little temporary teeth to fit in their immature, backtalking jaws. Once the bones of the cranium have developed to adult size the Tooth Fairy starts wiggling them at night and they fall out to the great satisfaction of parents and money hungry kids alike.

The process for initiating the formation of permanent teeth in humans is not completely understood. Normally, permanent teeth come in at about age six in humans and this appears to be part of a genetic development program whose temporal trigger is not yet known but may be the teeth jumping ship after being made to chew all sorts of stuff off the floor for the last five years.

There may be a few other factors as well, particularly expression of a protein called Pax-9, which is part of the paired box family of transcription factors. (Pax-9 should not be confused with K-Pax, that movie where Kevin Spacy thinks he’s an alien.)

(Transcription factors are proteins that bind to DNA and activate gene expression. The paired box family is a special class of transcription factors that govern pattern formation during organogenesis. These transcription factors were first discovered in fruit flies (love fruit, not gay). However, paired box genes are strongly conserved throughout evolution. In vertebrates they are implicated in the development of several tissues and organs, including the brain, limb muscles, kidney, eye, nose, and ear.)

Loss of Pax-9 function in humans is an extremely rare genetic disorder—known in just one family in the United States—but it results in the failure to produce adult molars and in the increased incidence of loss of the second premolars. This genetic link tells us that the switch for making adult teeth must involve inducing cells to make Pax-9.

A second genetic cascade, which occurs after Pax-9 expression, leads to the loss of milk teeth. The baby teeth start to get ‘wiggly’ because bone-remodeling cells dissolve the bony root and periodontal ligament by secreting digestive enzymes. It’s not know if these cells need this as food, or just like the taste.

As the enzymes break down the tooth root and surrounding connective tissue, the tooth loosens until it’s time for the old ‘dad and a string ploy’ to provide space for the adult tooth.

You'll need to take care of your teeth whitening on your on.

Why do we have wisdom teeth?

Tucked away at the back of your mouth are the the heavy mashers of the enamel world.

Anthropologists believe that your third set of molars (wisdom teeth), are the evolutionary answer to your ancestor’s early diet of coarse, rough food – like leaves, roots, and the occasional wiry squirrel – which required some major chewing power and resulted those little front teeth being worn down to useless nubbins in no time.

Your current diet with its softer foods and yogurt products (something your distant ancestors would have loved), along with marvels of modern technologies such as forks, knives, and Tom LeLanes new super-quite Juicer have relegated wisdom teeth to the status of just another lowly dental scare tactic. As a result, evolutionary biologists now classify wisdom teeth as vestigial organs, or body parts that have become functionless due to evolution. You know, like your coccyx.

From baby teeth to permanent teeth, tooth development lasts years. While your first molar erupts around the age of six and the second molar pokes it’s head above gum at around the age of 12, wisdom teeth, which begin forming around your tenth birthday usually don’t erupt until you are between the ages of 17 and 25. Because this is the age that you stop putting your body parts inside pencil sharpeners and pulling the ear hair out of feral dogs, the set of third molars has been nicknamed “wisdom teeth.”

Some people never get wisdom teeth, leading to the term ‘non-wisdom teeth people’, but for those who do, they may sprout anywhere from one to four – and, on very rare occasions, more than four. If you’re one of the unfortunates who get these extraneous, or supernumerary, teeth, it can lead to all sorts of problems.

Since human jaws are smaller than they used to be (possibly due to fashion), when wisdom teeth form they often become impacted, or suppressed, by the other teeth around them. (Evidently teeth are imperialist capitalists whose only wish is to subjugate their immediate neighbors.) If the tooth only partially erupts, food gets trapped in the gum tissue surrounding it which creates a perfect little home for bacteria leading to the potential for a serious infection and really bad breath. (Some people have bad breath without this.)

American Association of Oral and Maxillofacial Surgeons estimates that about 85 percent of wisdom teeth will eventually need to be removed. This dovetails nicely with the fact that Oral and Maxillofacial Surgeons are the ones who remove them.

The association recommends that patients remove wisdom teeth around 15 to 18 in order to “prevent future problems and to ensure optimal healing” and because no one cares if teenagers can’t talk for a week.