The Science of Discworld Revised Edition

planet that can still make it a bit fragile. If not kill it altogether.
    Which brings us back to our original question. Is life fragile, and have we been extraordinarily lucky? Or is it robust, and therefore common? Is life so adaptable that it can handle virtually anything that the universe sends its way?
    Until we can explore other worlds and see what kinds of life, if any, are present, anything we say here has to be speculative. The big difficulty is an ‘anthropic principle’ point. Suppose that life is incredibly rare, and that on most worlds it never really gets going, or doesn’t last long, because of all the disasters lying in wait. Nonetheless, there’s a lot of galaxies out there, each having billions or even trillions of stars. Even if the chances of survival are very, very small, occasionally one planet will get lucky. Some proportion of planets
must
get lucky, that’s how probability works.
    Because life on this world
has
survived, we are therefore one of the lucky ones. It then becomes completely irrelevant how small our chances were. We are not representative. The probability that we survived is certainty, because we
did
. So we cannot reason, from our existence, that the chance of survival has to be fairly large. Whether it is large or small, we are here. So this is a case where the anthropist can legitimately frighten us. Perhaps all planets do get life and, if they’re allowed enough time; even extelligent life on a few. But we really could be the only one who’s survived to ask the question.
    On the other hand … The very diversity of nasty things that the universe has up its sleeve argues for the adaptability and versatility of life. Life on Earth does not look like a bunch of lucky survivors. It looks like a bunch of tough guys who have overcome every obstacle put in their way. Sure, they took casualties, sometimes severe. But as long as a few survive the battle, pretty soon the planet is covered with life again, because life reproduces – fast. Whatever the disaster, it bounces back.
    So far, anyway.

THIRTY-THREE
THE FUTURE IS NEWT

    HEX WAS THINKING hard again. Running the little universe was taking much less time than it had expected. It more or less ran itself now, in fact. The gravity operated without much attention, rainclouds formed with no major interference and rained every day. Balls went around one another.
    H EX didn’t think it was a shame about the crabs going. H EX hadn’t thought it was marvellous that the crabs had turned up. H EX thought about the crabs as
something that had happened
. But it had been interesting to eavesdrop on Crabbity – the way the crabs named themselves, thought about the universe (in terms of crabs), had legends of the Great Crab clearly visible in the Moon, passed on in curious marks the thoughts of great crabs, and wrote down poetry about the nobility and frailty of crab life, being totally accurate, as it turned out, on this last point.
    H EX wondered: if you have life, then intelligence will arise somewhere. If you have intelligence, then extelligence will arise somewhere. If it doesn’t, intelligence hasn’t got much to be intelligent
about
. It was the difference between one little oceanic crustacean and an entire wall of chalk.
    The machine also wondered if it should pass on these insights to the wizards, especially since they actually lived in one of the world’s more interesting outcrops of extelligence. But H EX knew that its creators were infinitely cleverer than it was. And great masters of disguise, obviously.
    The Lecturer in Recent Runes had designed a creature.
    ‘Really, all we need is a basic limpet or whelk, to begin with,’ he said, as they looked at the blackboard. ‘We bring it back here where proper magic works, try a few growth spells, and then let Nature take its course. And, since these extinctions seem to be wiping out everything, it’ll gradually become the dominant feature.’
    ‘What’s the scale again?’ said Ridcully, critically.
    ‘About two miles to the tip of the cone,’ said the Lecturer. ‘About four miles across the base.’
    ‘Not very mobile, then,’ said the Dean.
    ‘The weight of the shell will certainly hamper it, but I imagine it should be able to move its own length in a year, perhaps two.’
    ‘What’ll it eat, then?’
    ‘Everything else.’
    ‘Such as …’
    ‘Everything. I’d advise suction holes around the base here so that it can filter seawater for useful things like