The barrier to change is not too little caring; it is too much complexity,” Bill Gates once opined, and he was right: many problems in development cannot be solved simply by wanting solutions badly enough. And yet when it comes to one of the key development outcomes, economic growth, the problem is not too much complexity, but not enough.

Complexity plays no obvious role in mainstream economics. Under the surface of traditional accounts of economic growth there is a rather crude model: economies are a bit like loaves of bread. They are made of two or three key ingredients, and bigger loaves simply have a bit more of everything.

Compare the economy of the UK with the economy of the Democratic Republic of Congo, a country with a similar population, and the textbook will say that the UK simply has more physical capital (factories, buildings, roads) and more human capital (education, training) and perhaps even better “institutions”. Of course, everyone knows that you cannot simply turn the DRC economy into the British economy by doubling the quantities of all the ingredients. The British economy is a different and more complex kind of thing altogether.