The Science of Discworld II

elvish interference.
    How did it actually happen on Roundworld? Here, the whole process took a mere five million years. One hundred thousand Grandfathers 2 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 tide.
    The same DNA evidence indicates that we and today’s chimpanzees parted company, specieswise, those five million years (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, Homo 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 cables from geostationary satellites, hang elevator compartments from them, equip them with suitable space elevator music … after which, leavingthe 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 Grandfathers 3 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