For the release of The Hobbit: The Desolation of Smaug, I interviewed biologist Dr Peter Hogarth of the University of York. He talked me through the history of dragons in folklore and literature, and their scientific plausibility. Fascinating stuff. Originally published on the Empire website.

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Smaug the Tremendous, the Chiefest and Greatest of Calamities, is one of a long history of literary and filmic dragons. “My teeth are swords, my wings a hurricane and breath death,” he boasts to Bilbo. But could such a creature ever have existed in the real world? “It’s highly improbable,” Dr Peter Hogarth of the University of York’s biology department patiently explains to us…

Before we start, Dr Hogarth, can you tell us a bit about yourself? How does a specialist in mangrove ecology and crustacea also become an expert on dragons?

It’s not really the day job. It’s a bit of nonsense, really. I’m a biologist, so I’ve always had an interest in the history of biology and people’s attitudes to animals. In the middle ages people obviously believed in dragons – mythical dragons but also as real animals. In the bestiaries and medieval collections dragons were kind of included with giraffes and real animals. Obviously what they knew about real animals wasn’t that different from what they thought they knew about the imaginary ones. An elephant is pretty improbable if you’ve never met one. So that’s how it all started. I wrote articles and one thing led to another.

Is there a single text where the first dragon appears: a sort of dragon ur-text?

You have to go back about four or five thousand years to the Ancient Near East for the first dragons. They were a sort of creation myth: a god slays a dragon and usually carves it up and makes the Heaven and Earth. The early dragons have most of the hallmarks of the ones we know now. They had large, reptilian, scaled bodies, horns, claws, they usually flew but not always – and they were slain. Dragon slaying is the hallmark of a proper dragon. They grow through a lot of classical myths like the Hydra, various other classical dragons, and the idea filtered through to medieval legends where a saint or knight slew the dragon, more-or-less as good overcoming evil. They’re given all sorts of unpleasant attributes, like they sometimes personify the devil. So if you were a saint you had to slay one, really. Then there are the folk myths which derive from that: a local guy kills a local dragon. Sometimes the place is specified with pinpoint accuracy. Eight or ten villages in North Yorkshire have their own dragon legend, and they’re all exactly the same: different name, different place but often identical circumstances. There were these myths of dragons that you would find in the next village if you were unlucky, or maybe at the back of a hill. The dragon in The Hobbit draws very much on the Anglo-Saxon dragons. Tolkien obviously was a very good Anglo-Saxonist.

Where does the fire-breathing come in?

The fire is interesting. Most of the dragons that are found in England – not much of Scotland, interestingly – and maybe parts of the continent, on the whole are in areas which the Romans occupied. It may be completely coincidental but the Roman historians talk about a battle between the Roman legions and the tribes of the east, and the tribes of the east had this dragon banner, apparently with some sort of pyrotechnics in it. It was said to breath fire – kind of psychological warfare, I guess. And then the Roman army adopted the dragon as their standard, a kind of windsock affair, and it then comes into heraldry. There’s a dragon standard flying above Harold in the Bayeux Tapestry. So there are a lot of rather complicated threads.

Actually, if you think of dragons flying in the air and then you see the Aurora Borealis or even a lightning storm, it’s not too much of a stretch to link the two things together: they’re not just dragons in the air, they’re fiery dragons. How else would you explain the aurora or lightning if you didn’t understand it? Nordic dragons were associated with burials and grave goods, treasure underground and death and destruction and maybe funeral pyres. It’s a bit vague but you can see some possible connections.

So is a dragon at all plausible as a real creature?

From a biological standpoint they couldn’t really have existed; not if you think of a dragon with wings and four legs, breathing fire. Once the idea’s there, they pick up characteristics from real animals. There are quite a lot of dragon “remains” in churches on the continent that look very much like stuffed crocodiles or a bit of a whale skeleton or something like that. Relics: a local saint slew a dragon and here’s the proof. There are certainly some accounts that sound very like garbled travellers tales of, say, pythons: there are stories of dragons that wound themselves round the thing they were attacking. Certainly once people had the idea of a dragon, a lot of things got mapped on to that idea. It’s a ferocious animal, obviously, so it’s going to have claws like other clawed animals, and big teeth and so forth. It’s oral history, so you can’t really know who said what to whom and how information got muddled up. It’s all fairly inferential but I’m broadly satisfied that one can join the dots.

Are the six limbs – two wings and four legs – at all feasible?

Basically dragons are vertebrates, and all vertebrates have four limbs. In birds two are wings and two are legs. A two-winged, two-legged dragon that didn’t breathe fire would be just about conceivable: not that different from a pterosaur. But the six limbs thing just isn’t possible, I’m afraid!

And is there anything in nature that does anything like breathe fire?

No. The nearest is the Bombardier beetle, which has a kind of explosive chamber in the general region of its anus, and actually mixes a couple of very reactive chemicals which explode. I forget what the temperature is. It’s not fire, but it looks a bit like an explosion.

You were involved in a Discovery Channel film where you tried to come up with a biologically plausible dragon. What were your solutions?

Well we had to “finesse” the skeleton: that was a bit of a cheat, really! But the main challenge for the programme was the problem of getting them airborne. They had to be big, and there are certain laws of physics you can’t quite get round. If it’s an animal that’s flying, there’s a certain relationship between the wing area and the mass. The bigger the mass, the bigger the wing area, and with very large animals there’s not enough room on the animal for big-enough wings. Then there’s a power issue: it’s hard work flying, which requires a lot of muscle, which adds to the mass.

What we did was try and ease the problem a little. Firstly, birds have air sacs as part of their respiratory system. Secondly, hydrogen is less dense than air. Thirdly, there are some bacteria that generate gaseous hydrogen. Fourthly, all animals have a very large population of bacteria in their gut. So we came up with the idea that bacteria would operate in the guts of the dragon to generate hydrogen which would be stored in these gas chambers which would lighten the whole animal.

Then there’s a trade-off between flying using the benefits of hydrogen, and fire. Hydrogen’s not that inflammable unless you have a match. The only way in which you can ignite gaseous hydrogen at a reasonable temperature, room temperature, is by using a catalyst, of which one is powdered platinum. If you chuck some powdered platinum into a test tube of gaseous hydrogen in the lab, it will explode. So that was what we worked on. We built into the storyline that dragons have to fly to some area and grind up minerals in their teeth to create the catalyst to explode the hydrogen. The problem with it is the more fire they breathed, the less buoyant they’d become! So it’s still highly improbable! But it was quite fun to kind of make it work.

Do you have a favourite movie dragon (aside from your own)?

Hmm… There are so many movie dragons. There are dragons as a species and individual dragons in particular stories… I think I’m more interested in the dragons that weren’t deliberately invented.