Problems of aging, shrinking population

The population of bugs in a Petri dish typically increases in an S-shaped curve. To start with, the line is flat because the colony is barely growing. Then the slope rises ever more steeply as bacteria proliferate until it reaches an inflection point. After that, the curve flattens out as the colony stops growing.

Overcrowding and a shortage of resources constrain bug populations. The reasons for the growth of the human population may be different, but the pattern may be surprisingly similar.


For thousands of years, the number of people in the world inched up. Then there was a sudden spurt during the Industrial Revolution that produced, between 1900 and 2000, a near quadrupling of the world’s population.

Numbers are still growing; but recently an inflection point seems to have been reached. The rate of population increase began to slow. In more and more countries, women started having fewer children than the number required to keep populations stable.

Four of nine people already live in countries in which the fertility rate has dipped below the replacement rate. Last year the United Nations said it thought the world’s average fertility would fall below replacement by 2025. Demographers expect the global population to peak at around 10 billion (it is now 6.5 billion) by mid-century.

The Economist