The Science of Discworld Revised Edition

of mammals, and anyway, intelligence is such a generic trick. So it seems likely that some other form of intelligent life would have evolved instead, though not necessarily adhering to the same timetable. On an alternative Earth, intelligent crabs might invent a fantasy world shaped like a shallow bowl that rides on six sponges on the back of a giant sea urchin. Three of them could at this very moment be writing
The Science of Dishworld
.
    Sorry. But it is true. But for a fall of rock here, a tidal pattern there, we wouldn’t have been us. The interesting thing is that we almost certainly
would
have been something else.
    1 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.
    2 According to the most recent dating methods, the Cambrian began 543 million years ago. The Burgess shale was deposited about 530–520 million years ago.
    3 In the words of Discworld’s God of Evolution: ‘The purpose of the whole thing is to
be
the whole thing.’

THIRTY-ONE
GREAT LEAP SIDEWAYS

    RINCEWIND WAS IN his new office, filing rocks. He’d worked out quite a good system, based on size, shape, colour and twenty-seven other qualities including whether or not he felt that it was a friendly sort of rock.
    With careful attention to cross-referencing, he reckoned that dealing with just those rocks in this room would take him at least three quiet, blessed years.
    And he was therefore surprised to find himself picked up bodily and virtually carried towards the High Energy Magic building holding, in one hand, a hard square light grey rock and, in the other hand, a rock that appeared to be well disposed to people.
    ‘Is this
yours
?’ roared Ridcully, stepping side to reveal the omniscope.
    The Luggage was now bobbing contently a few metres offshore.
    ‘Er …’ said Rincewind. ‘Sort of mine.’
    ‘So how did it get
there
?’
    ‘Er … it’s probably looking for me,’ said Rincewind. ‘Sometimes it loses track.’
    ‘But that’s another universe!’ said the Dean.
    ‘Sorry.’
    ‘Can you call it back?’
    ‘Good heavens, no. If I could call it back, I’d send it away.’
    ‘Sapient pearwood
is
meta-magical and will track its owner absolutely
anywhere
in time and space,’ said Ponder.
    ‘Yes, but not this bit!’ said Ridcully.
    ‘I don’t recall “not this bit” ever being recorded as a valid subset of “time and space”, sir,’ said Ponder. ‘In fact, “not this bit” has never even been accepted as a valid part of any magical invocation, ever since the late Funnit the Foregetful tried to use it as a last-minute addition to his famously successful spell to destroy the entire tree he was sitting in.’
    ‘The Luggage may consist of a subset of at least
n
dimensions which may co-exist with any other set of >
n
dimensions,’ said the Bursar.
    ‘Don’t pay any attention, Stibbons,’ said Ridcully wearily. ‘He’s been spouting this stuff ever since he tried to understand H EX ’s write-out. It’s completely gibberish. What’s “
n
”, then, old chap?’
    ‘Umpt,’ said the Bursar.
    ‘Ah, imaginary numbers again,’ said the Dean. ‘That’s the one he says should come between three and four.’
    ‘There isn’t a number between three and four,’ said Ridcully.
    ‘He imagines there is,’ said the Dean.
    ‘Could we get inside the Luggage in order to physically go into the project universe?’ said Ponder.
    ‘You could try,’ said Rincewind. ‘I personally would rather saw my own nose off.’
    ‘Ah. Really?’
    ‘But the thought occurs,’ said Ridcully, ‘that we can use it to bring things back. Eh?’
    Down under the warm water, the strange creature’s stone structure collapsed for the umpteenth time.
    A week went past. On Tuesday a left-over snowball collided with the planet, causing considerable vexation to the wizards and destroying an entire species of net-weaving jellyfish of which