Still, I never really mind bad service in a restaurant. It makes me feel better about not leaving a tip.

Our instinct may be to see the impossibility of tracking everything down as frustrating, dispiriting, perhaps even appalling, but it can just as well be viewed as almost unbearably exciting. We live on a planet that has a more or less infinite capacity to surprise. What reasoning person could possibly want it any other way?

Maine is wonderful. It can be very hard. I mean, if you look at the profile maps it doesn't look it, but somehow when you get out there it's really steep and hard.

No one knows, incidentally, why Australia's spiders are so extravagantly toxic; capturing small insects and injecting them with enough poison to drop a horse would appear to be the most literal case of overkill. Still, it does mean that everyone gives them lots of space.

There is something about the momentum of travel that makes you want to just keep moving, to never stop.

My favourite fellow of the Royal Society is the Reverend Thomas Bayes, an obscure 18th-century Kent clergyman and a brilliant mathematician who devised a complex equation known as the Bayes theorem, which can be used to work out probability distributions. It had no practical application in his lifetime, but today, thanks to computers, is routinely used in the modelling of climate change, astrophysics and stock-market analysis.

There is more difference between a zebra and a horse, or between a dolphin and a porpoise, than there is between you and the furry creatures your distant ancestors left behind when they set out to take over the world.