And the fire-breathing?
    This particular aspect of dragon-lore took me a while to figure out because fires don't occur in any known biological system.  Lightning and lava are usually responsible for fires in nature, and when humans achieve it, we do so by striking metals or oxidising chemicals together.  How do we rationalise a fire-breathing animal? 
    In the Christian Bale movie Reign of Fire, dragon breath is explained as dragons producing a natural napalm which they spit out.  That's creative and all, but the problem is that flammable or incendiary chemicals don't catch fire on their own.  They need an ignition source.  
    The more I thought about it, the more frustrated I got.  Fires typically burn at hundreds of degrees celsisus and even birds, the warmest-blooded creatures on Earth, rarely exceed forty.  It didn't seem there was any way of justifying an animal getting things hot enough to start a fire. 
    Until I remembered bombardier beetles....  
   Bombardier beetles possess one of the most chemically remarkable adaptations in nature.  When threatened, two glands in their bodies eject separate streams of hydrogen peroxide and paraquinone which blend together in mid-air.  When mixed, these chemicals form a jet so hot it reaches the boiling point of water, burning any predator away.
    Paraquinone and hydrogen peroxide are also irritant chemicals so it’s a wonderful defence mechanism…if you try to attack a bombardier beetle, it pees boiling poison in your face.  Fun fact, John Cusack repels people the same way.   
    So, here’s what I’m thinking.  Suppose our dragons had similar glands in their throats to bombardier beetles.  They could spit out a chemical cocktail close to 100 degrees Celsius and that might be enough to achieve ignition.  Most substances need to be scraped, scratched or electrocuted to catch fire but there are a few which ignite when you simply warm them.
    Triethyl borane, for example, will catch fire at -21 degrees.  That would do the trick but it's probably not a good idea because the body temperature of the dragon would set fire to it as soon as the gland produced it.   
    White phosophorus catches at body temperature of course, but it’s a solid powder.  Powders take weeks to form inside a body (think of kidney stones) and presumably the dragon will want to use its fire-breath regularly, meaning we want something that a gland can produce at short notice.
    That leaves carbon disulfide, a colourless liquid which catches fire at 90 degrees, roughly the same temperature of a bombardier beetle jet.  Carbon disulfide can cause erectile dysfunction in humans but, to my knowledge, nobody has ever tested this on dragons so there’s no reason to assume it would cause any harm. 
    If we therefore propose that a dragon has three glands in its mouth, one for paraquinone, one for hydrogen peroxide and one for carbon disulfide, when all three squirt together they could theoretically create an honest-to-god biologenic flame-spray on demand! 
    So while dragons might not exist on Earth there's no reason they couldn't exist in nature.  In fact, given the sheer size of the Universe and the number of potentially inhabited planets, there may even be a world on which dragons have actually evolved. 
    And there you have it.  We've entertained a crazy idea, but rather than justifying it by saying "magic did it" or appealing to some other unprovable notion, we've used facts we already know to be true.  And this is how Scientists speculate.  Sticking to the laws of nature doesn't mean you have to abandon extravagant dreams.  In fact, sticking to the laws of nature can sometimes make your dreams possible.

Image credits:
Dragon lady whose name I forget: highfidelitynotes
Dragonlab: aalabor
Sad Vampire: deviantart
Humbaba: wikipedia
Dragon at war: wired
Bombardier Beetle: typseofinsects

I've never heard of it...
    The idea isn't talked about much these days, but I can fill you in fairly quickly.  Life-Force is a 1985 sci-fi horror movie directed by Tobe Hooper about aliens who dehydrate people to death, based on a Colin Wilson novel, The Space Vampires.  And I'm not making this up. 
    Today it's a celebrated cult classic, famous for a young Patrick Stewart cameo and because the main character, played by Mathilda May, spends the whole film needlessly naked as she strolls around killing.  Fun fact: the original poster had to be recalled because it featured May's nipples and the family version (below) had to be issued with lens flares painted over them.  They don’t make sci-fi movies like they used to…perhaps that’s a good thing.
    The movie got its title from an ancient, pre-Scientific idea called "life-force" or "vital essence" - a mysterious property all living things were believed to have.  The assumption was that studying Biology was distinct from Chemistry and Physics, because living things were somehow separate to the crude matter of the inorganic world.  
    Supposedly, it wasn't possible to explain living phenomena without including this soul-subtance, and for centuries Biology was fused with philosophy, mysticism and magical thinking.  Until Science destroyed it.
    There are some hangers-on who still talk about living “energy” or “aura”, but people who trust things like clear definitions or the logic of parsimony have long abandoned the idea of life-force.  Thanks to Science, we now know life isn't the result of some boring, primitive notion like magic.  Life is Physics and Chemistry at their most complicated and beautiful.  Here's how we figured that out in nine experimental steps.

Step 1 - Camera Obscura
    The first hint that life-force might be unnecessary was uncovered by the Muslim scholar Abu Al Hasan.  I’ve mentioned Al-Hasan in another blog because he essentially invented the Scientific method itself.  The thing he's best known for however, is explaining how pin-hole cameras work. 
    If you make a tiny hole in the wall of an otherwise dark room or box, light from outside will project itself onto the far wall, creating a perfect image of the external world.  This effect had been known since ancient times, but Al-Hasan successfully explained it as the geometric behaviour of light-beams moving in straight lines.
    After building a number of pin-hole cameras with lenses to prove his idea, Al-Hasan got hold of a bull’s carcass and extracted its eyeball for comparison.  Following a rather unpleasant dissection, Al-Hasan found that the retina of an eye behaves identically to the back wall of a camera.  The pin-hole (pupil) allows light to enter and light-beams create a retinal image according to his geometric laws.  There was no need of magic.  Apparently you could explain the very nature of visual perception using only a basic appreciation of optics. 

Step 2 - Doctor Death
    Up until the 16th century, medicine was built on the work of the philosopher Hippocrates of Kos.  Hippocrates never got his hands dirty with actual dissection of course, he just used intuition (guessed) and doctors learned their trade by reading his books and watching occasional amputations.  It wasn’t until 1543 that a scientist named Andreas Vesalius decided to carry out genuine human autopsies and record his discoveries. 
    Vesalius began his career as a grave robber, unearthing bodies and dissecting them at his laboratory.  This may sound immoral by today's standards, but if you want to make an omelette you’ve got to dig up a few cadavers. 
    Fortunately when he moved to Italy, he fell into favour with Charles V, who not only patronised Vesalius' research but began scheduling executions to match his lecture schedule so he would always have a fresh supply of corpses.  Doctors of the city would be invited along and Vesalius became a morbid celebrity who would take the freshly killed criminal and cut them open as his assistants created diagrams for medical textbooks. 
    And, astonishingly, Vesalius began to discover that the human anatomy was not particularly different to that of animals.  We had the same stuructre, the same organs and our skeletons differed only by shape and size.  It would appear that ancient wisdom was wrong; humans were another breed of animal rather than a separate classification.  Life-force was still part of the deal, but it was disconcerting to realise we probably shared the same life-force with dogs and cats.
    This idea was heretical of course.  You weren’t supposed to challenge the accepted wisdom of ancient thinkers, so it was assumed that the human body had simply changed form in the years between Hippocrates and Vesalius.  The idea of throwing out an incorrect theory when contrary evidence arose wasn’t a big thing back then. 
    It was also Vesalius' discoveries which stirred up the first notions of ethical vegetarianism.  If humans were made of meat just like every other animal, did we truly have the right to kill and eat other animals?  Was it really that different from eating human meat?     

Step 5 - You are all diseased
    In the 1700s, the British navy was in trouble.  More than 50% of its sailors were dying from scurvy; a horrible condition which causes your teeth to fall out, your skin to split open and you to die.  Nobody could figure out what was going on until 1747 when the physician James Lind carried out the first medical trial in history. 
    Lind decided to run experiments on the crews of various ships, administering different diets to different sailors.  Some were given cider to drink, some were given sulfuric acid, some vinegar, some oranges and (as a control group) some had to drink equal amounts of seawater.  The results were clear: sailors who consumed oranges didn’t get scurvy.
    By 1794 other foods like sauerkraut, lemons and limes were also shown to prevent scurvy and it became standard practice for ships to have a supply of citrus fruits on board (hence British sailors being nicknamed “limeys” by yanks).  Finally, in the 1930s, the active ingredient preventing scurvy was identified by Norman Haworth as Vitamin-C (ascorbic acid).
    It turns out that while most animals produce their own, a small number of species including monkeys, apes and bats do not make Vitamin-C.  As a species, humans suffer from inherent Vitamin-C defficiency, which makes things uncomfortable for the life-force hypothesis.
    If living things are bestowed with magical essence, why was it missing Vitamin-C?  Why would humans and bats be born with a genetic disease while other animals get excused such a handicap?  If life-force existed it was imperfect and incomplete…which sounds more like a natural, random chance thing than an ethereal, magic spirit thing.  Incidentally, one other animal which lacks Vitamin-C?  Guinea Pigs.

Step 9 - Soup's Up!
    By the 1950s Darwin’s theory of natural selection was so well-evidenced, it was accepted that life on Earth originated from a common ancestor billions of years ago.  The only question was how that life got there in the first place.
    It was one thing to say living things are today the result of biochemistry, but the initial spark which gave rise to proteins, enzymes and information chains was still unexplained.  It was sometimes nicknamed “Darwin’s Black Box” because nobody could figure out how to get life from a sterile Earth.  So naturally people plugged life-force into the epistemological gap.
    But then, in 1953, Harold Urey and Stanley Miller decided to replicate the conditions which had birthed Biology.  By stewing all the chemicals known to exist on Earth at the time (easily learned from studying rocks, ice cores and cosmic nebulae), they filled a flask with methane, ammonia, hydrogen, water and began spark-plugging this "primordial soup" to simulate lightning.
    After a week the soup had changed composition entirely.  It was filled with amino acids, the building blocks of proteins and enzymes.  If it was possible for lifeless chemicals to synthesise amino acids in a few days, imagine what could be achieved in a few hundred million years with a churning ocean, lightning, hydrothermal vents, rock pools, ultra-violet rays and so on. 
    (NB: some people have mistakenly criticised the experiment because along the road to making amino acids, the Miller-Urey experiment also made cyanide and formaldehyde, which are obviously poisonous, leading to fallacious rejection of the results.  What's not being understood by these people is that the cyanide and formaldehyde are part of the sterile mixture of chemicals...if you react them long enough they do make amino acids, that's the whole point of the experiment.)
    The final “missing link” between these amino acids and simple proteins has not yet been discovered, however.  We’ve figured out step 1 of the life process, and we know steps 4,5,6,7... etc, but we’re missing a few steps in between.  It is here that the remaining spiritualists and witches set up camp, insisting life-force must exist within those few question marks left in the chain. 
    As a Scientist, I have to concede that they may be right.  However, I think it’s unhealthy to cling to an un-evidenced hypothesis.  Furthermore, the history of Biology has shown that the more we’ve studied it, the smaller life-force’s reach has become. 
    It makes sense that early explanations for living things would favour magic over testable laws of Science...nobody knew any testable laws of Science!  But now that our knowledge has matured, I think we can safely shrug off the cloak of mysticism.  We cannot know with certainty of course, but wisdom suggests that life-force has been truly  sucked dry.

Image credits:
Soul leaving body: YouTube
Life-Force poster: thecultmoviereview
Look into my eye: giphy
Hannibal Lecter: wikipedia
Shameless Plug: shamelessplug7
Guinea Pig 1: imgflip
Guinea Pig 2: angryapps
Dorothy Hodgkin: thefamouspeople
Pain in the ass frog: knowyourmeme
Buchner: wikimedia
Primordial Soup: defendingthebible