'He means no magic mirrors, no crystal balls,' said Ponder. 'Nothing that people expect to be magical. No people at all, where we're going. Put Hex down. We'll be back instantly, in any case.

Ready, Hex?'

For a moment the circle glowed, and the wizards vanished.

Dr Dee turned to the Librarian.

'It works!' he said. 'The Great Seal works! Now I can—'

He vanished. And the floor vanished. And the house vanished. And the city vanished. And the Librarian landed in the swamp.

'What a piece of work is a man! How noble in reason! How infinite in faculty! In form, in moving, how express and admirable! In action how like an angel! In apprehension how like a god!'

But you wouldn't want to watch him eat, close up ...

William Shakespeare was another key figure in the transition from medieval mysticism to post- Renaissance rationalism. We were going to mention him, but we had to wait for him to turn up in Roundworld.

Shakespeare's plays are a cornerstone of our present Western civilisation.27 They led us from a confrontation between aristocratism, barbarism and tradition-bound tribalism into real civilisation as we know it. And yet ... he seems to be a contradiction: uplifting sentiments in a barbarous age. That's because he was standing at a pivot point in history. The elves have been seeking something that will become human, and will interfere with Roundworld to make sure they get it. Humans are superstitious. But the human condition can also create a Shakespeare.

Though not in this version of history.

The elves aren't the only Discworld inhabitants that have interfered with Roundworld: the wizards have tried some 'uplift' of their own, in the sense of David Brin, and using the techniques of Arthur C. Clark near the end of The Science of Discworld, the apes of Roundworld are sitting in their cave, watching a manifestation from another dimension, an enigmatic black rectangular slab ... The Dean of Unseen University taps on it with his pointer, to attract attention, and chalks the letters R-O-C-K. 'Rock. Can anyone tell me what you do with it?' But all the apes are interested in is S-E-X.

The next time the wizards look at Roundworld, the space elevator is collapsing. The planet's inhabitants are heading out into the universe on vast ships made from the cores of comets.

Something very dramatic has happened between the apes and the space elevator. What was it?

The wizards have no idea. They doubt very much it could have had much to do with those apes, who were very much The Wrong Stuff.

In the first volume of The Science of Discworld, we explored no further. We left a gap. It was a tiny part of the historical record on the geological timescales that governed everything up to the ape, but rather a big gap in terms of changes to the planet. But now even the wizards are aware that the apes, unpromising material as they may have been, did in fact evolve into the creatures that built the space elevator and fled from a very dangerous planet in search of, as Rincewind would put it, a place where you are not hit on the head with rocks on a regular basis. And, apparently, a key step in their evolution was elvish interference.

How did it actually happen on Roundworld? Here, the whole process took a mere five million years. One hundred thousand Grandfathers28 ago, we and the chimpanzees shared a distant ancestor. The chimpanzeelike ancestor of Man was also the Manlike ancestor of the chimpanzee.

To us, it would have looked astonishingly like a chimpanzee -but to a chimpanzee, it would have looked astonishingly like a human.

DNA analysis shows, beyond any shadow of reasonable doubt, that our closest living relatives are chimpanzees: the ordinary ('robust') chimpanzee Pan troglodytes and the more slender

('gracile') bonobo Pan paniscus, often politically incorrectly called the pygmy chimpanzee. Our genomes have 98 per cent in common with both, leading Jared Diamond to refer to humans as

'the third chimpanzee' in a book of the same title.

The same DNA evidence indicates that we and today's chimpanzees parted company, specieswise, those five million yean (100,000 Grandfathers) ago. That figure is debatable, but it can't be very far wrong. The gorillas split off a little earlier. The earliest fossils of our 'hominid'

ancestors are found in Africa, but there are numerous later fossilised hominids from other parts of the world such as China and Java. The oldest known are two species of Australopithecus, each about 4-4.5 million years old. The Australopithecines had a good run: they hung around until about 1-1.5 million years ago, at which point they gave way to genus Homo: Homo rudolfensis, Homo habilis, Homo erectus, Homo ergaster, Hot heidelbergensis, Homo neanderthalensis, and finally us, Homo sapiens. And somehow another Australopithecine inserted itself into the middle of those Homos. In fact the more hominid fossils we find, the more complicated our conjectured ancestry becomes, and it now looks as if many different hominid species coexisted on the plains of Africa for most of the past five million years.

Today's chimpanzees are quite bright, probably a lot brighter than the apes that the Dean tried to teach spelling to. Some remarkable experiments have shown that chimps can understand a simple version of language, presented to them as symbolic shapes. They can even form simple concepts and make abstract associations, all within a linguistic frame. They can't build a space elevator, and they never will unless they evolve considerably and avoid being killed for 'bush meat'.

We can't build one either, but it might take no more than a couple of hundred years before the things are sprouting all along the equator. All you need is a material with enough tensile strength, perhaps some composite involving carbon nanotubes. Then you dangle cable from geostationary satellites, hang elevator compartments from them, equip them with suitable space elevator music ... after which, leaving the planet becomes entirely straightforward. The energy cost, hence the marginal financial cost, is near enough zero, because for everything that needs to go up, something else needs to come down. It could be moon rock, or platinum mined in the asteroid belt, or the astronaut that the person going up is due to replace on duty. The capital cost of such a project is enormous, though, which is why we're not in any great hurry right now.

The big scientific problem in this connection is: how can evolution get so quickly from an ape that can't compete mentally with a chimpanzee to a godlike being that can write poetry as good as Shakespeare's, and has advanced so rapidly from that point that it will surely soon erect (drop)

a space elevator? 100,000 Grandfathers hardly seems long enough, given that it took about 50 million Grandfathers29 to get from a bacterium to the first chimpanzee.

Something that dramatic needed a new trick. That trick was the invention of culture. Culture allowed any individual ape to make use of the ideas and discoveries of thousands of other apes. It let the ape collective acquire knowledge cumulatively, so that it didn't all get lost when its owner died. In Figments of Reality we coined the term 'extelligence' for this suite of tricks, and the word is beginning to become common currency. Extelligence is like our own personal intelligence, but it lives outside us. Intelligence has limits; extelligence is infinitely expandable. Extelligence lets us pull ourselves upwards, as a group, by our own mental bootstraps.

The contradiction between Shakespeare's noble sentiments and the heads-on-spikes culture in which he lived is a consequence of his position as a very intelligent intelligence in a not-veryextelligent extelligence. Many individuals possessed the nobility to qualify for Shakespeare's praise, but their as yet rudimentary extelligence had not yet transmitted that nobility into the general culture. The culture was, or claimed to be, noble in principle -kings taking their authority from God Himself -but it was a barbarian style of nobility. And it was welded to a barbarian cruelty, the kings' means of self-preservation.