We got a cat because we didn't like them much.

Our garden was debated territory between five local cats, and we'd heard that the best way to keep other cats out of the garden was to have one yourself.

A moment's rational thought here will spot the slight flaw in this reasoning. However, if you're predisposed to keep cats, rational thought has nothing to do with it. We've never met anyone who recalls waking up one day and thinking: “This morning I will go shopping and buy some sprouts, one of those blue things for the lavatory, some baking foil—and, oh yes, a cat would be nice.”

Cats have a way of always having been there even if they've only just arrived. They move in their own personal time. They act as if the human world is one they just happened to have stopped off in, on their way to somewhere that is possibly a whole lot more interesting.

And what, when you come right down to it, do we know about them? Where did they come from? People say, well, evolution, it stands to reason. Why? Look at dogs. Dogs descended from wolves. You can tell. Some dogs are alsatians, which is just a wolf in a collar, biding its time. And then there's all these smaller dogs, going down in size until you get the weird little ones with lots of Zs in their name which squeak and can get into pint mugs. The point is, you can see the evolution happening, all the way from hairy semi-wolves to bald yappy things bred to go up Emperor's sleeves or whatever.

You know that if civilisation suddenly stopped, if great clanking things from Alpha Centauri suddenly lurched out of the sky and spirited mankind away, the dogs would be about two meals away from becoming wolves.

Or look at us. Some of the details might be a bit fiddly, but we—bright, civilised us, who know all about mortgages and non-stick saucepans and Verdi—can look back over our genetic shoulders and see a queue of stumbling figures going all the way back to little crouching shapes with hairy chests, no forehead and the intelligence of a gameshow audience.