Should this change the way we live? The population has exploded in the last two hundred years. Now it is going into reverse. Experts worry this could be one shock too many.
Human race has reached its peak say experts
Fertile ground: When agriculture was invented there were just 15 million humans on Earth. Glossary
Fertility rates - The number of children born, on average, to each woman within a studied group. A total fertility rate of 2.1, is the minimum needed for a population to remain steady and is known as the "replacement rate".
Replacement rate - The rate of births needed for babies to replace their parents.