YOU'VE heard of peak oil, but an even more important concept is peak babies.

When will we stop adding to the world's population and increasing our need for more oil and other limited resources?

Falling ... the average number of children per woman has dropped to 2.4. Credit:iStock

The world answer is now: the average number of children per woman has dropped to 2.4, which means once those kids grow up, the world's population will thereafter replace itself but grow no more.

Equilibrium - 10 billion people, up from 7 billion now - will be achieved by the end of this century.