Everything starts somewhere, although many physicists disagree.

     But people have always been dimly  aware of the problem with  the start of things. They wonder aloud how the snowplough driver gets to work,  or how the makers  of dictionaries look up the spelling of  the words. Yet there is the constant desire to find some point in the twisting, knotting,  ravelling nets of space-time on  which a metaphorical finger  can  be  put to indicate that here, here, is the point where it all began...

     Something began when  the Guild of Assassins  enrolled Mister  Teatime, who  saw things differently from other people, and one  of the ways that  he saw things differently  from other  people was  in  seeing  other  people as things  (later, Lord Downey of the Guild said, 'We took  pity on him because he'd  lost both parents  at an  early age.  I think that,  on reflection, we should have wondered a bit more about that.')

     But it was much earlier even than that when most people forgot that the very oldest stories are,  sooner or  later, about blood. Later on  they took the blood out to make the  stories more acceptable to children,  or at least to the people  who had  to  read them  to children  rather than the children themselves (who,  on the whole, are quite keen on blood provided  it's being shed by the deserving

     And earlier still  when  something in the darkness of the deepest caves and  gloomiest forests  thought: what  are  they,  these creatures?  I  will observe them.

     And  much, much earlier  than  that,  when  the Discworld  was  formed, drifting onwards through space atop four elephants on the shell of the giant turtle, Great A'Tuin.

     Possibly, as it moves,  it gets tangled like a blind man in a cobwebbed house in those highly specialized little spacetime strands that try to breed in every  history they  encounter,  stretching  them  and breaking them  and tugging them into new shapes.