What explains the hockey-stick shape of world GDP over time, with seemingly no progress for thousands of years, followed by soaring growth?

The first question you might ask is: is this just an exponential curve? If so, then the explanation is simple: we see a constant growth rate every year, and the steep upward slope is just what exponential curves look like. There’s no more mystery than there would be about the shape of a population curve.

To check this, we can plot the same numbers on a logarithmic y-axis. In such a chart, exponential curves become straight lines. But when we do this, we still see an upwards slope. That is, the growth rate has increased over time:

Nor is it just a consequence of population growth, because we see the same pattern in GDP per capita:

I’ve previously said that a core reason for this is that progress compounds, creating a flywheel effect. Here’s another way of looking at the same idea. Why wasn’t the threshing machine invented in, say, the 1300s? Consider all the barriers to such a thing:

Human capital

First, who would have invented it?

Would it have been a farmer? (Well over half the workforce were farmers.) When would he have found the time to tinker? Labor productivity and incomes were low; there wasn’t much spare time or material for inventing.

Who else could have done it? There was no established professional class of inventors, engineers, or entrepreneurs. The closest were skilled craftsmen who made machines, such as clockmakers or millwrights. Overall there were many fewer inventors per capita than today (ok, I don’t have data on this right now, but I’m pretty confident in this assertion).

If it were, say, a millwright, he would have to learn enough about machines to go beyond the kinds that he had been taught to make through apprenticeship, and invent something entirely new. Where would this knowledge have come from? There was no printed material, and no mechanics’ institutes.

And if our inventor did have mechanical skill, why why would he decide to apply it to a practical invention for farmers? It was more prestigious and lucrative to make clockwork novelties for the aristocracy. Even if the inventor did have a practical bent, there were social taboos against labor-saving devices.

Manufacturing

Suppose that despite all of this, some inventive person is determined to make a thresh...

Industrial progress