Rapid population growth is a very new phenomenon. After 300,000 years on the planet, we only hit one billion people in 1804. That doubled 123 years later. Since 1974 we have added another billion every 12-14 years.¹

Now that trend is coming to an end just as quickly. According to one estimate, we might be back down to 2 billion by 2400.

This is because most countries today have fertility ratesThe 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". that are below the replacement rateThe rate of births needed for babies to replace their parents. . In order for the population to remain steady, every couple needs to have 2.1 children on average.

But in most of the world it is below that. Africa has the highest rate at 4.5, but that is a fall from 6.6 in 1980, and it keeps dropping.

The whole of human progress has taken place against a backdrop of population growth. So we simply have no idea what a world with falling birth rates looks like.

Experts worry that having fewer people means fewer ideas, inventions, discoveries. Progress could grind to a halt.

Some say it is difficult to halt the fall in birth rates because it is driven by people's own preferences. 

For the first time in history most people can choose the size of their family. And it turns out they tend to want fewer children than they had in the past. That means all we can do, they say, is try to adapt ourselves to it.

But others think we are misreading the data. Fertility rates, they say, do not drop just because people want fewer children. It is because we make it very difficult for them.

Children are extremely expensive. It is estimated that it costs as much as £200,000 to raise a child.² If people had better jobs and cheaper options for childcare, they would be able to afford more children.

Yes: The way we live our lives today is based on the assumptionSomething which is thought of as true without proof. of endless population growth. It is going to be a mighty shock to the system when it goes into reverse.

No: Humans are very adaptableCapable of of modifying or adjusting. Modern biologists see humans as the most adaptable of all animal species.. We took rapid population growth in our stride, and we will easily be able to manage the opposite. We should not worry about making dramatic changes now.

Or... The problem is not with the way we live. Right now we are discouraging people from having children with high costs and poor work. Change that, and the population will stabilise.

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. 

Assumption - Something which is thought of as true without proof.

Adaptable - Capable of of modifying or adjusting. Modern biologists see humans as the most adaptable of all animal species.