And rather blows it, for the answer is in his question.

But I should like to concentrate on the non-economic elements of all this. What is the attitude of mind that has turned the most educated and prosperous part of the human race against reproducing itself?

It is also an entirely economic answer. The reason that the most educated and prosperous do not have great tribes of children is because they are educated and prosperous. We can see this in any indicator we like: whether it’s average income in a country, the wealthier within a society, the richer people are the fewer children they have. The effect is even more striking for education of women: more years in school leads to fewer changing nappies. This much is simple.

But of course we want to know why this is as well. Why should anything from learning to read and write to a PhD in electrical engineering lead to women wanting fewer children? Why does having the physical wherewithal to provide a child with an entrancing life lead to having fewer? And it isn’t just that children are a cost now as they weren’t in peasant societies, as Moore mentions.

It is, I’m afraid, our old economists’ friend, opportunity costs. The price of anything is not what we pay for it, it is what we give up to get it. The richer you are and the more educated you are the more glorious opportunities this modern world of ours gives you. You can travel the world, climb mountains, have a long and fulfilling career, run a major corporation, write novels, this globe of ours really is the mollusc of your choice. You can also spend some 30 years or so pumping out and raising (clearly, for men, only the latter) a series of five or eight children as our forbears did. But what you cannot do is all of them, choices have to be made.

The result of such is that given the multitude of choices available to the educated and prosperous fewer such are deciding to have children. That’s pretty much it.