<h2 class="wp-block-heading eplus-wrapper">What's happening?</h2>

Today there are more than eight billion people on the planet.

But now scientists think the number of humans is going to start shrinking. By 2400, they think, we might be back to two billion.

To make sure that a country's populationAll of the people that live in a place. does not fall, each couple needs to have 2.1 children on averageTypical or usual. . This replaces each parent - and then the .1 makes up for anybody that does not have children. It is called the replacement rateThe rate of births needed for babies to replace their parents. .

<h2 class="wp-block-heading eplus-wrapper">Find out more </h2>

But most of the world is below that. This is a huge change for the world. The population has always grown. Some people now worry about the future.

So why are people having fewer children? Some think it is because people do not want lots of children.

Others think there is a different reason. Having children can cost a lot of money, and many people think they simply do not have enough money to give children a good life.

Yes! We need to get used to the idea of a world with fewer, but older, people. And we should change how we live so that people have enough money to have children.

No! Humans are very good at changing so they fit in with what is happening around them. We should not worry too much about the future.

Population - All of the people that live in a place.

Average - Typical or usual.

Replacement rate - The rate of births needed for babies to replace their parents.