World population is the sum of its parts and those parts move in very different ways.
A little while ago, when world population was about 7 billion (bn), there was an easy way to remember how it was distributed, which was as follows:
1bn Europe
1bn the Americas
1bn Africa
1bn China
1bn India
2bn the rest, mainly Asia excluding China and India
In rich countries, with good state provision of health and welfare, population is already mostly stable or falling. This applies in Europe, North America and parts of Asia, notably Japan. China is an anomaly, with stable/falling population resulting from the one child policy.
In poor countries, that don't have good state provision of health and welfare, population is still rising. Parents have lots of children to try to make sure that they have people to look after them when they get old, because they can't call on the state. This is mainly Africa, plus parts of Asia and South America.
As economic development takes place, countries move from the growth group to the stable/falling group. But there is a time lag for this because increased longevity means that for a while the population continues to increase, and it also takes time for fertility rates to reduce. In the latter case by far the most effective policy is education for girls. Taking all this together, that's why global population is expected to peak towards the end of this century. By that time, very few countries will still have rising populations, and lots will have falling populations.
Another way to look at population distribution is, as the statisticians love to say, broken down by age and sex. State health and welfare systems need workers and businesses to make money that can be taxed to fund health and welfare. If the number of economically inactive people, mainly children and pensioners, is too big a proportion of the total, then there aren't enough economically active people to pay the taxes that fund health and welfare. Many of the countries with stable or falling population are already falling into this trap.
And technology isn't the panacea that some hope it to be, because it is harder to tax a robot than to tax a human worker. It is possible to tax the companies that make and own the robots, but set those tax rates too high and the robots don't get made.
It is nonsense to suggest that there isn't space for more people. The UK is one of the more densely populated countries in the world, but only 6 per cent of land is built on. In Surrey golf courses take up more land than houses. Resource constraints are becoming more significant, as recent price rises for energy and food are demonstrating. But here in the south and east of England, we are just waking up to the realisation that the biggest constraint on development and population will be water supply.
