So, if people didn’t settle down to take up farming, why then did they embark on this entirely new way of living? We have no idea – or actually, we have lots of ideas, but we don’t know if any of them are right. According to Felipe Fernández-Armesto, at least thirty-eight theories have been put forward to explain why people took to living in communities: that they were driven to it by climatic change, or by a wish to stay near their dead, or by a powerful desire to brew and drink beer, which could only be indulged by staying in one place.

It is a curious feature of our existance that we come from a planet that is very good at promoting life but even better at extinguishing it.

Australians are very unfair in this way. They spend half of any conversation insisting that the country's dangers are vastly overrated and that there's nothing to worry about, and the other half telling you how six months ago their Uncle Bob was driving to Mudgee when a tiger snake slid out from under the dashboard and bit him on the groin, but that it's okay now because he's off the life support machine and they've discovered he can communicate with eye blinks.

Life just wants to be; but it doesn't want to be much.

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.

But I got a great deal else from the experience. I learned to pitch a tent and sleep beneath the stars. For a brief, proud period I was slender and fit. I gained a profound respect for the wilderness and nature and the benign dark power of woods. I understand now, in a way I never did before, the colossal scale of the world. I found patience and fortitude that I didn't know I had. I discovered an America that millions of people scarcely know exists. I made a friend. I came home.

If you go out on the Appalachian Trail, you have to bring so much more equipment - a tent, sleeping bag - but if you go hiking in England, or Europe, generally, towns and villages are near enough together at the end of the day you can always go to a nice little inn and have a hot bath and something to drink.