Terry Pratchett - The Science of Discworld

  If William of Occam had been a wizard at Unseen University, he would have grown a beard.

  [38] The quantity of bacon per trotter is on averageslightly more than one quar­ter of the amount per head.

  [39] Wizards seldom bothered to look things up if theycould reach an answer by bickering at cross-purposes.

  [40] To the best of our knowledge, based on deductionfrom the available evi­dence. Certainly it was a big extinction - far bigger than the one that killed off (or helped to kill off) the dinosaurs. We remember the dinosaur one because they’ve had such good PR people.

  [41] There’s a silly reason for this, and a sensible one.The silly reason is that species are usually defined to be different if they don’t interbreed. If two sep­arate species don’t interbreed, it’s difficult to put them back together again. The sensible one is that evolution occurs by random mutations - changes to the DNA code ­followed by selection. Once a change has occurred, it’s unlikely for it to be undone by further random mutations. It’s like driving along country roads at random, reaching some particular place, and then con­tinuing at random. What you don’t expect is to reverse your previous path and end up back where you started.

  [42] According to the most recent dating methods, theCambrian began 543 mil­lion years ago. The Burgess shale was deposited about 530-520 million years ago.

  [43] In the words of Discworlcd’s God of Evolution:’The purpose of the whole thing is to be the whole thing.’

  [44] Indeed, it is a fundamental part of story telling. Ifthe hero did not overcome huge odds, what would be the point ?

  [45] Possibly he was holding a large axe at the time.

  [46] Readers of the Discworld book The Last Continent will recall that, by an amazing coincidence, beetles were something of a passion for the God of Evolution.

  [47] Rincewind would add some more:

  ’Is it safe?’

  ’Are you sure?’

  ’Are you absolutely sure?’

  [48] A worse case is what used to be called Eohippus, the Dawn Horse - a beau­tiful, poetic name for the animal that formed the main stem of the horse’s family tree. It is now called Hyracotherium, because somewhat earlier some­body had given that name to a creature that they thought was a relative of the hyrax, represented by a single fossil shoulder-blade. Then it turned out that the bone was actually part of an Eohippus. Unfortunately, whoever officially names a species first must get priority, so now the Dawn Horse has a silly, unpoetic name that commemorates a mistake.

  We lost ’Brontosaurus’ -thunder-lizard - for a similar reason. Thunder Lizard ,,. what a marvellous name. ’Apatosaurus’? It probably means ’Gravitationally challenged Lizard’.

  The moral of this tale is that when learned committees of elderly scientists meet to discuss an exceptional issue they can always be trusted to make a com­pletely ridiculous decision. Quite unlike the wizards of Unseen University, naturally.

  [49] Lots of ammonite species died out 5-10 millionyears before the K/T boundary, so it looks as if their extinction genuinely was gradual. But what­ever it was that happened at the K/T boundary finished them off.

  [50] OK, if you insist ... Our favoured line here is ’hairy’. But hairs don’t fos­silize, so how can you tell? If you have hair, you need grooming. All over the body. This requires flexible backbones, and you can tell how flexible they are from the shape of the vertebrae. Which do fossilize. (Sometimes scientists can be very ingenious.) Evolution crossed that line about 230 million years ago.

  [51] How many recipe books do you have that tell youto boil water, but never specify the altitude at which this should be done? It matters: higher up, water boils at lower temperatures.

  [52] There was a television programme called The Magic Roundabout. One of the characters was a dog called Dougal, which looked a bit like a hairbrush. Mauds shrimps have the same general form, though not with hair.

  [53] This is probably another lie. Alien microbes areunlikely to find us edible. So are alien tigers, although they might do us quite a lot of damage in finding out. But certainly an alien world will have a whole host of nasty surprises, if we are not very careful. We can’t tell you what they’ll be. They’ll be a surprise.

  [54] We apologize to any real gods.

  [55] Unfortunately, huge malicious destructive force isa god-like power.