I have on the shelf another of Lewis's novels, The Extraordinary Reign of King Ludd, set in an alternate history where the 1848 revolutions succeeded and the crowns of the British and Mughal Empires were united in marriage. Eighty years on, King-Emperor George Akbar I is struggling with technology; I don't remember a lot else except that I think there was another revolution at the end.

I got hold of The Evolution Man (aka What We Did to Father aka How I Ate My Father aka Once upon an Ice Age) after reading Terry Pratchett's repeated recommendations in A Slip of the Keyboard. It really is hilarious, a novel of cavemen who talk to each other in mid-twentieth century schoolboy prose, with names like Oswald, Ernest and Wilbur - clearly aimed in part at William Golding's The Inheritors, and perhaps also at any number of caveman films. Their father worries about which end of the Pleistocene era they are living at, but invents fire, thus causing a technological revolution. I'm sure that the young Douglas Adams must have read it too; there are strong echoes of the humour of Hitch-hiker here, if anything more so than of Pratchett (though there are shades of Lewis's the treatment of technology in the early Rincewind/Twoflower relationship). It's a very short book at 120 pages, and there really is only one joke, but it's worked through in several different variations to a satisfactory and tasty conclusion.