Terry Pratchett - The Science of Discworld I

Of course, evolution may sometimes hit on 'designed' solutions, as happens for the eye. Sometimes it hits on solutions that do have a narrative, but we fail to appreciate the story. Stick insects look like sticks, and their eggs look like seeds. There is a kind of Discworld logic to this, since seeds are the 'eggs' of sticks, and prior to the the­ory of evolution taking hold the Victorians approved of this 'logic' because it looked like God being consistent. The early evolutionists didn't see it that way, and they worried about it; but they worried a lot more when they found that some stick insect eggs looked like lit­tle snails. It seemed silly for anything to resemble the favourite food of nearly everything else. In fact, it seemed to be a flat contradiction to the evolutionary story. The puzzle was solved only in 1994, after forest fires in Australia. When new plant shoots came up out of the ashes, they were covered in baby stick insects. Ants had carried the 'seeds', and the 'baby snails', down into their subterranean nests, thinking they were the real thing. Being safely underground, the stick insect eggs escaped the fires. In fact, baby stick insects look, and run, just like ants: this should have been a clue, but nobody made the connection.

And sometimes evolution's solution has no narrative structure. To test Darwin's theories thoroughly, we should be looking for evolved systems that don't conform to a simple narrative descrip­tion, as well as for ones that do. Many of the brain's sensory systems may well be like this. The first few layers of the visual cortex, for example, perform generalized functions like detecting edges, but we have no idea how lower layers work, and that may well be because they don't conform to any design principles that we cur­rently can recognize. Our sense of smell seems to be 'organized' along very strange lines, not at all as clearly structured as the visual cortex, and it too may be lacking any element of design.

More importantly, genes may well be like this. Biologists habit­ually talk of 'the function of a gene', what it does. The unspoken assumption is that it does only one thing, or a small list of things. This is pure magic: the gene as a spell. It is conceived as being a spell in the same sense that 'Cold Start' in a car is. But a lot of genes may not do anything that can be summed up in a simple story. The job they evolved to do is 'build an organism', and they evolved as a team, like Thompson's circuits. When evolution turns up solutions of this kind, conventional reductionism is not much help in under­standing those solutions. You can list neural connections till the cows come home, but you won't understand how the cows' visual systems distinguish a cowshed from a bull.

RINCEWIND WAS FINDING, now that he was back at what appeared to be his real size, that he was com­ing to enjoy this world after all. It was so marvellously dull.

Every so often he'd be moved forward a few tens of millions of years. The sea levels would change. There seemed to be more land around, speckled with volcanoes. Sand was turning up on the edge of the sea. Yet the sheer vast ringing silence dominated everything. Oh, there'd be storms, and at night there were brilliant meteor showers that practically hissed across the sky, but these only underlined the absent symphony of life. He was rather pleased with 'symphony of life'. 'Mr Stibbons?' he said. 'Yes?' said Ponder 's voice in his helmet. 'There seem to be a lot of comets about.' 'Yes, they seem to go with roundworld systems. Is this a prob­lem?'

'Aren't they going to crash into this world?' Rincewind heard the muted sounds of debate in the back­ground, and then Ponder said: 'The Archchancellor says snowballs don't hurt.' 'Oh. Good.' 'We're going to move you on a few million years now. Ready?'

'Millions and millions of years of dullness,' said the Senior Wrangler.

'There are more blobs today,' said Ponder.

'Oh, good. We need more blobs.'

There was a yell from Rincewind. The wizards rushed to the omniscope.

'Good heavens,' said the Dean. 'Is that a higher lifeform?' 'I think? said Ponder, 'that seat cushions have inherited the world.'

They lay in the warm shallow water. They were dark green. They were reassuringly dull.

But the other things weren't.

Blobs drifted over the sea like giant eyeballs, black, purple, and green. The water itself was covered with them. A scum of them rolled in the surf. The aerial ones bobbed only a few inches above the waves, thick as fog, overshadowing one another in their fight for height.

'Have you ever seen anything like that?' said the Senior Wranger.

'Not legally,' said the Dean. A blob burst. Audio reception on the omniscope was not good, but the sound was, in short, phut. The stricken thing disappeared into the sea, and the floating blobs closed in over it.

'Get Rincewind to try to communicate with them,' said Ridcully.

'What have blobs got to talk about, sir?' said Ponder 'Besides, they're not making any noise. I don't think phut counts.'

'They're various colours,' said the Lecturer in Recent Runes. 'Perhaps they communicate by changing colour? Like those sea creatures...' He snapped his fingers as an aid to memory.

'Lobsters?' the Dean supplied.

'Really?' said the Senior Wrangler. 'I didn't know they did that.'

'Oh yes,' said Ridcully. 'Red means "help!" [39] Wizards seldom bothered to look things up if they could reach an answer by bickering at cross-purposes. '

'No, I think the Lecturer in Recent Runes is referring to squid,' said Ponder, who knew that this sort of thing could go on for a long time. He added hurriedly, 'I'll tell Rincewind to give it a try.'

Rincewind, apparently knee deep in blobs, said: 'What do you mean?'

'Well ... could you get embarrassed, perhaps?'

'No, but I'm getting angry!'

'That might work, if you get red enough. They'll think you want help.'

'Do you know there's something else here besides blobs?'

Some of the blobs trailed strands in the faint breeze blowing across the beach. When they tangled up on a blob gasbag, which put some stress on the line, the little blob on the end let go its grip on a rock, the line gradually shortened, and the gasbag bobbed onwards with its new passenger.

Rincewind saw them on a number of blobs. The blobs did not look healthy.

'Predators,' Ponder told him.

'I'm on a beach with predators?'

'If it really worries you, try not to look blobby. We'll keep an eye on them. Er ... the Faculty is of the opinion that intelligence is most likely to arise in creatures that eat lots of things.'

'Why?'

'Probably because they eat lots of things. We'll try a few big jumps in time, all right?'

'I suppose so.'

The world flickered ...

'Blobs.'

...flickered...

'The sea's a lot further away. There's a few floating blobs. More black blobs this time.'

... flickered ...

'Well out at sea, great rafts of purple blobs, some blobs in the air.'

...flickered ...

'Great steaming piles of onions!' 'What?' said Ponder.

'I knew it! I just knew it! This whole damn place was just lulling me into a false sense of security!' What's happening?' 'It's a snowball. The whole world's a giant snowball!'

THE EARTH HAS BEEN A GIANT SNOWBALL on many occasions. It was a snowball 2.7 billion years ago, 2.2 billion years ago, and 2 billion years ago. It was a really cold snowball 800 million years ago, and this was followed by a series of global cold snaps that lasted until 600 million years ago. It reverted to snowball mode 300 million years ago, and has been that way on and off for most of the last 50 million years. Ice has played a significant part in the story of life. Just how significant a part, we are now beginning to appreci­ate.