If, as seems to be the case everywhere, culture works by faithful imitation with a bias towards imitating prestigious individuals (in other words, copy the expert, not the parent or the person closest to hand), then all it would take for certain skills to be lost would be a handful of unlucky accidents in which the most prestigious individual had forgotten or mislearned a crucial step or even gone to his grave without teaching an apprentice.

The most striking case of technological regress is Tasmania. Isolated on an island at the end of the world, a population of less than 5,000 hunter-gatherers divided into nine tribes did not just stagnate, or fail to progress. They fell steadily and gradually back into a simpler toolkit and lifestyle, purely because they lacked the numbers to sustain their existing technology.

Today’s container ships go not much faster than a nineteenth-century steamship and today’s internet sends each pulse little quicker than a nineteenth-century telegraph – but everybody is using them, not just the rich. ... Now almost everybody can afford the cheap goods carried by container ships; almost everybody can afford the internet; almost everybody can afford to travel by jet. ... The story of the twentieth century was the story of giving everybody access to the privileges of the rich, both by making people richer and by making services cheaper.

For instance, as evolutionary psychologists confirm, sometimes the motivation behind conspicuous displays of virtue by the very rich are far from pure. When shown a photograph of an attractive man and asked to write a story about an ideal date with him, a woman will say she is prepared to spend time on conspicuous pro-social volunteering. ... (A man in the same ‘mating-primed’ condition will want to spend more on conspicuous luxuries, or on heroic acts.)

It follows that spillover – the fact that others pinch your ideas – is not an accidental and tiresome drawback for the inventor. It is the whole point of the exercise. By spilling over, an innovation meets other innovations and mates with them.

After all, even the cleverest in-house programmer is unlikely to be as smart as the collective efforts of ten thousand users at the ‘bleeding edge’ of a new idea. ... In product after product on the internet, innovation is driven by what Eric von Hippel calls ‘free-revealing lead users’: customers who are happy to tell manufacturers of incremental improvements they can suggest, and of unexpected things they have found they can do with new products. ... The world is turning bottom-up again; the top-down years are coming to an end.

Collaboration between unrelated strangers seems to be a uniquely human achievement. In no other species can two individuals that have never before met exchange goods or services to the benefit of each other, as happens routinely each time you visit a shop or a restaurant or a website. ... Yet human beings can treat strangers as honorary friends.