||The growth of the human population might be seen as an indication of success, but usually it is seen as a problem. From time to time to provokes a near panic, as it did when Malthus wrote An Essay on the Principle of Population (1798) and again when the Erlichs wrote The Population Bomb. Not only does population grow inexorably, it does so at an increasing rate and the rate of increase is fastest among groups least able to provide for their children. Concern is increased by the fact that wherever such runaway population growth occurs in nature it is followed by a collapse in numbers. Malthus spelt out the problem starkly: populations have the capacity to grow by geometric progression while food supply only increases by arithmetic progression. Unless the growth of population is held back by moral restraint it will be held back by famine, disease or war: the so called â€˜Malthusian checksâ€™.
The idea of geometric progression is now more commonly known as exponential growth and is most easily understood as growth with a constant doubling time. For most of prehistory there were only a few million people alive. By the time of Christ there were about 300 million. The population took 1,500 years to double, 300 years to double again and only 150 years to double again, reaching 2.4 billion by 1950. In the next 30 years it doubled again, passing 5 billion in 1987. The growth rate peaked at 2.1% per annum between 1965 and 1970, but even at the current growth rate of 1.7% per annum, it would double again in another 40 years. No wonder there is such concern about what will happen in the next century.
Some indication of what might happen can be gained from analysis of current and past variation in growth rates in different kinds of country. At present Africa has the fastest rates of growth, averaging 3% (and in Kenya well over 4%), indicating a doubling time of under 20 years. Then come tropical South America, 2.6%, and South Asia, 2.3%. China and temperate South America have intermediate rates of growth around 1.3%. Lower rates occur in the former USSR, US and the lowest are in Europe, where a few countries have reached zero growth. With the exception of China\'s draconian population policy, the main influence on these rates seems to be the length and success of the period of industrialization, though culture also exerts an influence.
A more detailed understanding of population growth requires separate analysis of fertility and mortality. In pre-industrial societies both fertility and mortality rates were high, so life expectancy was short. As Europe industrialized in the 19th century, diet, sanitation and medicine improved and the mortality rate fell, triggering a rapid growth of population. After a few decades, the fertility rate also fell, reducing the rate of growth. This change from high to low fertility and mortality is known to demographers as the demographic transition. Unfortunately, it has not proved easy to reproduce this transition elsewhere. Mortality control is relatively easy to achieve, but fertility control relies on a shift in the behaviour of whole populations and has proved much more difficult. Economic prosperity alone is not sufficient, as shown by high fertility in the oil-rich states of the Middle East. Compulsion is only partially successful, as shown by experience in China and India. Provision of contraceptives has limited effects unless people are committed to their use. Education and the changing status of women are part of the pattern. A shift from a way of life where children support their parents in old age to one where parents support their children through a long period of education may be the decisive one. But, such is the variability with which fertility and mortality have changed in different countries, predictions are very difficult. They are even more difficult when many countries have populations growing faster than their rate of economic growth so that income per capita is falling.
The UN publishes population forecasts, with a range from optimistic to pessimistic, but even their optimistic forecast envisages a world population of 7.5 billion in 2025. Even with the assumption that all countries will reduce fertility to replacement levels, the UN envisages world population reaching 10 to 14 billion before stabilization. This will pose a serious challenge to human society and place massively increased pressures on the environment. Achieving sustainable development in these circumstances will require concerted international action, but there is little sign that it will be forthcoming, indeed the opposite seems true. As most of the growth will be in less-developed countries, there will be strong incentives for international migration, and the developed countries seem to be tightening controls in anticipation. The stage is set for internal and international conflicts over migration which may well be a step towards a world dominated by Malthusian checks. PS
Further reading Ehrlich, The Population Bomb.