The Science of Discworld Revised Edition

carted off in a UFO, then the burden of proof shifts dramatically and evidence of abduction stronger than sincere expressions of belief becomes necessary.
    Reports of alien abductions are not new. Back in the Middle Ages , however, they would have been either flights on witches’ broomsticks or encounters with fabulous creatures like the succubus, a demon in a woman’s body who allegedly had sex with men while they slept. The witches of Discworld employ broomsticks for transport only. The sex bit doesn’t appeal to them at all – except for Nanny Ogg, of course.
    Folk tales of succubi and their like can be found worldwide. In Newfoundland people tell of an ancient hag sitting on their chests at night, and in Vietnam they speak of the ‘grey ghost’. What seems to be going on is some common mental pattern, overlaid with cultural influences. That’s why abductions by witches riding broomsticks have gone out of vogue, but abductions by aliens riding UFOs are flavour-of-the-decade.
    Susan Blackmore thinks that all of these experiences are, and were, caused by sleep paralysis. This is a feature of the mind that prevents sleeping people from moving their limbs as they would if they were acting out their dreams. Such a ‘mental switch’ is important for any animal that dreams: you don’t really want to go sleepwalking out of your cosy burrow and straight down a predator’s throat. Plenty of mammals dream – most of us have seen a cat or dog asleep with its legs twitching, and the evidence from recordings of the brain’s electrical activity is that the animals are engaged in something that closely resembles the brain activity of a dreaming human. We can’t be sure whether cats have visual dreams like we do, but sleep and dreaming take place in primitive parts of the brain, so they probably go back a long way in our evolutionary history. At any rate, if the sleep paralysis system malfunctions, people who are partially awake may undergo sleep paralysis. Experiments show that in such cases they typically get a strong impression that ‘somebody is there’.
    This feature of the human mind may go back to the time, just after the meteorite hit, when the nocturnal mammals suddenly awoke in a world without dinosaurs. Their senses of hearing and sight, previously separate from each other because they had evolved at very different periods and in very different circumstances, would have become linked together. When their ears heard something strange , their visual sense would kick in and make them feel that they could
see
what was causing it. We inherited this tendency, but we interpret it in terms of the current culture: bogeymen, witches, maybe even dragons a few centuries ago, aliens with big black eyes today. The sexual link is straightforward, too: dreams about sex are very common anyway.
    Oh, yes, one more thing: since we’ve all watched
Close Encounters
, we know exactly what an alien must look like … just as everyone used to know that witches soared through the air on a broomstick. So our visual system knows what shape it should give to whatever it
sees
when we get that funny feeling that something is haunting us. And flying saucers have come on nicely, too, from being the rivet-studded things that were all the rage in galactic circles in the early Fifties.
    Stories of people seeing ghosts may well have the same explanation. You’ve read the tales, you know what a ghost ought to look like (maybe you watched
Ghostbusters
or a Stephen King movie), and you’re trying to sit up all night in the Haunted House. You’re thinking about ghosts, about headless horsemen and Elizabethan ladies who walk through walls and go transparent – and then you start to doze off because it’s 2 am and you’ve been up all night … The sleep paralysis circuit glitches …
Aaaaagh!
    1 Ok, if you
insist
… Our favoured line here is ‘hairy’. But hairs don’t fossilize, so how can you tell? If you have hair, you need grooming. All over the body. This requires flexible backbones, and you can tell how flexible they are from the shape of the vertebrae. Which do fossilize. (Sometimes scientists can be
very
ingenious.) Evolution crossed
that
line about 230 million years ago.
    2 How many recipe books do you have that tell you to boil water, but
never
specify the altitude at which this should be done? It matters: higher up, water boils at lower temperatures.

FORTY-ONE
DON’T PLAY GOD

    THE ARCHCHANCELLOR WAS rather quiet over