30,000 years ago: 

Five miles under the Alps, where the pressure was so intense and the darkness so fertile that it managed to squeeze a life out of nothingness, Eve woke up, and wanted to know who she was. She knew she existed, because she was thinking, but she didn't know what it was that was doing the thinking, or how.

The first thing she did was imagine a space for herself to be in, and the living rock shuffled up to make room for her. It shrank back from her outstretched hand to form a dark, dripping cave.

Next, she discovered that she could feel, and spent a few minutes happily patting the rocks, enjoying their slick and jagged texture. Then she raised her hands to her face and felt its contours – much softer and squishier than those of the rocks, much harder to read. She wanted to see herself, but, never having encountered anything like a mirror, she imagined herself the way she had imagined the cave. 

She made a replica of herself – a sister – as accurate as she could make it from simply feeling her face in the darkness. It was prettier than her: its face was more symmetrical, its chin stronger, its mouth broader. But it burned with the same curiosity, and it was soon discovering its own senses, running its hands over the slick outcrops of rock.

Later, when Eve had seen such a thing as a mirror, she called her Mirror – or Myrrha, as it came to be spelled after her sojourn in Ancient Greece. But for now, she just called her sister.

Eve saw her own nature reflected in her sister's face, but she found that it answered nothing. Her nature was unformed. The only thing she knew about herself was the fact that she wanted to know. 

Still, she welcomed the company. She imagined more caves and more tunnels for them to explore, and the rock bowed its head to her like a faithful servant. Stalactites grew down from the ceiling to touch her hair. If she wandered off a ledge, the rock rose up to meet her. If she tried to climb, a sheer wall would arrange itself into steps beneath her feet.

And so the two just-born girls wandered through the darkness under the world hand-in-hand, always climbing, always looking for new things to see. After days or months of this, they came to a place where the rocks would no longer obey Eve. It was quite easy to spot. The currents of air were fresher, and kissed their faces with a slight breeze. But it was only an accidental kiss, and not a kiss of allegiance.

Myrrha and Eve concluded that this was no longer their realm, but they still wanted to see it. Besides, they soon discovered that Eve could make an opening into 'the deep world', as they called it, wherever she was, just by tracing the outline of a door in the air and grasping an imaginary handle. 

Eve couldn't make steps anymore, so they clung on to handholds in the rock, clambered over ledges, all the time guessing, with the utmost excitement, what they would find around the next bend in the tunnel. And this new realm wasn't inert. As they went on, they discovered spiders, centipedes, and best of all, bats – chittering and swooping, hanging from the ceiling like curled-up leaves. 

Eve fell in love with them at once. She spent so long trying to get one to land on her outstretched arm that even Myrrha got bored and dragged her away, promising new wonders – maybe even better than bats – in the next cave.

Then, so slowly that they didn't realize what was happening at first, daylight filtered down to them, dividing things, infusing them with colour, giving them a finer level of detail. The world that they had thought so lovingly simple became a lot more complicated then. But neither of them could have guessed how complicated it would get when they encountered human beings.

First came a cave of red hand-prints. Eve and Myrrha measured their own hands against them and giggled. Then came a huge cavern filled with animal-paintings in shades of ochre-red, clay-brown, charcoal-black and sulphurous yellow. Black bulls and round-bellied horses, woolly rhinoceroses butting horns, cave lions with sleek muzzles and serenely-closed eyes. Everything was infused with a sense of motion, because the cave-walls were so uneven, and the light played such devilish tricks.

Eve stared in wonder. And back in her realm, the mud quickened, the pools began to stir and bubble with life. New eyes drank up the darkness.

Even when she saw the real creatures depicted in these paintings, she couldn't have been more charmed than this. The infinite variety of life – with all its smells and calls and textures – was nothing compared with the kind of creature who would try to represent it so faithfully. The demons took on the shapes of the creatures Eve saw there – they had horns and antlers and claws – but they were animated by the mysteries and inconsistencies of humanity. That would be her real passion, in every one of her lives.

After that cave of pointless but powerful ingenuity, the revelation of the sun, the sky, the Alpine-landscape, seemed rather tame. Eve didn't want to look at any of it until she had found the cave-painters.

They turned out to be a hunter-gatherer tribe living just below the snow-line in a valley of scrub and gravel and icy streams. They used the caves for ceremonies, so when they saw Eve and Myrrha wander out – as naked as new-born babes, and only slightly cleaner – they assumed they were visitors from the spirit world.

The humans were extremely respectful at first, because it wouldn't do to upset ladies from the spirit world. They gave them food, which Myrrha and Eve discovered they could eat with pleasure, and showed them their tools, their shelters, their animal-skin cloaks, as though they were asking, 'Is this all right?'

Because they were women, Eve and Myrrha learned women's arts – though, at that point in history, women's arts were surprisingly useful: spinning and medicine and food preparation. For a while, the girls became merry spies: learning the arts of civilization, and then passing them on to the just-born creatures in the deep world, who had bat-like wings, or coral-branching antlers, or stomping hooves, but were all – for the moment – as gentle as their mistress.

Fire was another thing that set the character of the deep world. Eve loved it from the moment she saw it. It seemed to dance just like the paintings in the caves, but it had a trajectory she could never anticipate. It burned her half a dozen times before she was induced – by pain and Myrrha's exasperation – to keep her hand away. When she saw it sulk and smoke among the dry grasses, and then suddenly lift up its head and crackle, she laughed with delight. 

She loved fire so much that, when they next opened the door to the deep world, it was everywhere – blazing on the surface of the black lakes, smouldering in the crags, hissing and crackling and filling the silence with steam.

This first encounter with humanity ended badly, just like the rest of them would. The chief of the tribe wanted Eve to mate with him. And she tried it, because she always wanted to try everything, but she giggled the whole time, and he got offended.

And then one day he saw them opening the door to their underground world, and they both understood instantly – although they had known nothing but wonder all their lives – that he was going to kill them. 

Eve pushed Myrrha through the door to safety, and a moment later the thread of her consciousness was cut. 

***

Myrrha couldn't say that she saw the other demons collapsing beside her. She couldn't say that she saw Eve being clubbed to death before the door closed. She guessed later – centuries later – that these things had happened, and imagined she'd seen them. Or she remembered seeing them, and they came back to her as a guess – she was never sure which.

There was nothing for a long time. A dreamless sleep. Myrrha never knew if the deep world still continued during these periods of sleep, or if it just winked out of existence until it was needed again. Would a wanderer in the dark come across dozens of caves full of sleeping figures? The point was moot anyway, because nobody could get into the deep world when her sister was gone. 

For the moment, Myrrha slept the sleep of the dead, and it made no practical difference whether she was really dead or not.

But one of the tribe had made a little clay figurine representing the strange girl from the spirit world. It was passed down from mother to daughter, and then carelessly shattered, and then pieced back together by a woman with a sympathetic imagination.

It was such an unlikely confluence of circumstances, and yet it happened again and again down the centuries. Something about Eve's nature – and human nature – made it inevitable. People were always moved to make representations of her. There was something girlish and yet ancient, inoffensive and yet terrifying, about her, and you wanted to understand, after she was gone, what it was that had made her seem so spooky. Those representations were almost always destroyed by a ruling class who felt threatened – because she was female, or because they hadn't understood why they were so spooked by her either. And a woman with the very womanly virtues of patience and imagination would find the pieces and love them to life again.

And, every time she awoke, the lives of the demons were embellished and enriched, and then cut tragically short again. It was never more than a few years. They had barely shaken the dust off their shoulders when they were scythed down, to commune with the dust once more.

It was insupportable – a horrible accident that kept happening because nobody would learn. That was the beginning of Myrrha's rebellion. But it was a long time before she had the courage – or the desperation – to act on her thoughts. Both these things came to her at the same time, in the city of Oxford – the courage from Doctor Faustus, and the desperation from Robin Crake.