INTERNATIONAL TRADE IS like sex, The Economist would say. Each generation thinks that it has discovered it for itself. In fact, the proportion of most countries’ GDP that is traded internationally has remained remarkably stable over the past hundred years. But the overall volume has gone up so much that globalisation seems like something new. The Silk Road shows us just how little human nature has changed, how adventurous and profit-minded our forebears were. It comes as a shock – rather as if one found explicit sepia photographs of one’s grandparents experimenting in depraved positions.