It took 13 years for the human population of Earth to grow from 6 billion to 7 billion and 12 years to grow from 5 billion to 6 billion; this is the first time in our history that the rate of population growth, which has been growing exponentially since the first homo sapiens, has actually slowed.

So what does this mean for our future? "On the bright side, the long-dreaded resource shortage may turn out not to be a problem at all, " writes Wise. "On the not-so-bright side, the demographic shift toward more retirees and fewer workers could throw the rest of the world into the kind of interminable economic stagnation that Japan is experiencing right now."

In Western Europe the problem of shrinking population is by now so familiar that the Germans have even invented one of their famous portmanteau words for it: Shrumpfgesselschaft or "shrinking society".

Fears of human population outstripping the Earth's resources go back thousands of years. The work of 19th century economist Thomas Malthus is famous, but did you know that Plato and Aristotle also broached the topic back in the 4th Century BC?

The notion that we might precipitate our own extinction by choosing not to reproduce is rather more novel, however. As Wise points out, while we know how to restrain birth rates (educate women), government attempts to encourage parenthood in countries such as Singapore and Sweden have so far been largely unsuccessful.