The Science of Discworld Revised Edition

tribe rushed out of the waves and swung up into the nearby mangrove trees. A shadow sped beyond the surf and headed back into the blue water, to an unregarded chorus of simian catcalls and mangrove seeds.
    ‘Oh yes, and they like throwing things,’ said the Senior Wrangler.
    ‘Seafood is good for the brain, my granny always said,’ said Ridcully.
    ‘This lot couldn’t eat too much of it, then. Yell, throw things, and prod stuff to see what it does, that’s the extent of their capabilities. Oh,
why
didn’t we discover the lizards earlier?
They
had
class
.’
    ‘Wouldn’t have stopped the snowball,’ said Ridcully.
    ‘No. You were right, Archchancellor. It’s so
pointless
.’
    The three wizards stood looking gloomily out to sea. In the middle distance, dolphins stitched their way across the water.
    ‘Should be coming up to coffee time,’ said the Dean, to break the silence.
    ‘Good thinking, that man.’
    Rincewind was wandering in the next bay, staring at the cliffs. Oh, things were killed off on the Discworld, but … well …
sensibly
. There were floods, fires and, of course, heroes. There was nothing like a hero for a species whose number was up. But at least some actual thought went into it.
    The cliff was a series of horizontal lines. They represented ancient surfaces, some of which Rincewind had virtually walked on. And in many of them were the bones of ancient creatures, turned into stone by a process Rincewind did not understand and rather distrusted. Life had some how come out of the rocks of this world, and here you could see it going back. There were whole layers of rock made out of life, millions of years of little skeletons. Faced with a natural wonder on that scale, you could only be overawed by the sheer chasms of time or else try to find someone to complain to.
    A few rocks fell out, halfway up the cliff. A couple of small legs waved uncertainly in the strata, and then the Luggage tumbled out, slid down the pile of debris at the foot of the cliff, and landed on its lid.
    Rincewind watched it struggle for a while, sighed, and pushed it the right way up. At least some things didn’t change.

FORTY-TWO
ANTHILL INSIDE

    YOU KNOW WHAT’S going to happen to the apes – they’re going to turn into
us
. 1 But why do we have them playing in the surf? Because it’s fun? Yes … but more significantly, because the seashore is central to one of the two main theories about how our ape ancestors acquired big brains. The other, more orthodox theory places the evolution of the big brain out on the African savannahs, and we
know
that some of our ancestors lived on the savannahs because we’ve found fossils. Unfortunately, seashores aren’t a good place to leave fossils. You often
find
them there, but that’s because they were deposited when the area wasn’t a seashore at all, and the sea has subsequently eroded the rocks to expose the fossils. In the absence of direct evidence of this kind, the surfing apes theory has to take second place … but it does explain our brains rather neatly, whereas the savannah theory rather sidesteps this issue.
    Our closest living relatives are two species of chimpanzee: the standard boisterous ‘zoo’ chimp
Pan troglodytes
and its more slender cousin the bonobo (or pygmy) chimp
Pan paniscus
. Bonobos live in very inaccessible parts of Zaire, and weren’t recognized as a separate species of chimpanzee until 1929. We can to some extent unravel the past evolutionary history of the great apes by comparing their DNA sequences. Human DNA differs from the DNA of either chimpanzee by a mere 1.6% – that is, we have 98.4% of our DNA sequences in common with theirs. (It is interesting to speculate on what the Victorians would have made of this.) The two species of chimpanzee have DNA that differs by only 0.7%. Gorillas differ from us, and from both chimps, by 2.3%. For orangutans, the difference from us is 3.6%.
    These differences may seem small, but you can pack an awful lot into a small percentage of an ape genome. A big chunk of what we have in common must surely consist of ‘subroutines’ that organize basic features of vertebrate and mammalian architecture, tell us how to be an ape, and tell us how to deal with things we’ve all got – like hair, fingers, internal organs, blood … The mistake is to imagine that everything that makes us human and not a chimpanzee must live in that other 1.6% of ‘special’ DNA – but DNA doesn’t work that way. For