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7 BILLION OF US: THE VIEW BY LANCET INFECTIOUS DISEASES

Wednesday, 2nd of November 2011

  

 ‘Recent history shows us that people will limit their own fertility if they have a high degree of confidence that their children will reach adulthood.’

• 7 BILLION OF US

The Lancet Infectious Diseases, Volume 11, Issue 11, Page 801, November 2011

Original Text

The Lancet Infectious Diseases

On Oct 31, 2011, the human population will likely reach 7 billion. The event has special resonance for the author of this editorial, who is expecting to become the father of a child who will contribute to our passing this milestone. That planet Earth now supports more people than have lived in all of human history is cause for reflection on how we got here, and what might be done to produce a stable population with an acceptable quality of life.

The rapid growth in our number has taken place only in the past 200 years. As detailed in The State of World Population 2011, a report from the UN Population Fund (UNFPA), it was as recently as 1804 that the human population reached 1 billion, after which things started to speed up: 2 billion in 1927, 3 billion in 1959, 4 billion in 1974, 5 billion in 1987, 6 billion in 1999, and 7 billion in 2011. It is a reasonable assumption—and a sobering thought—that the human population has doubled during the lifetimes of most readers of this journal.

Population growth (or decline) is determined by a complex interplay of mortality and fertility. Since the early 1950s, average life expectancy worldwide has risen from 48 years to about 68 years for men and 72 years for women. Worldwide, infant mortality has declined from 133 deaths per 1000 births in the 1950s to 46 per 1000 now. Great disparities exist, of course: in sub-Saharan Africa, life expectancy at birth is 54 years for men and 56 years for women, whereas in high-income countries the numbers are 75 years and 82 years. Similarly, mortality under the age of 5 years in 2009 was 130·1 per 1000 livebirths in sub-Saharan Africa versus 7·1 in high-income countries.

Fertility rate, defined as the average number of children a women is likely to have during her childbearing years, has declined worldwide in the past 60 years from about six to 2·5. Again there are disparities: 1·7 births in developed counties—well below the rate of 2·1 at which women have enough babies to replace themselves in the population—versus 4·8 in sub-Saharan Africa. Fertility falls with economic development and reductions in poverty, which go hand in hand with improvements in maternal and child health, the education of women, and their empowerment over reproductive choices. By some predictions, the world population will peak at around 10 billion before the end of this century; however, for this to happen the fertility rate must continue to fall.

The human population is both younger than before and getting older. 43% of the world's population is younger than 25 years. Conversely, there are now about 900 million people older than 60 years worldwide, and that number is predicted to increase to 2·4 billion by the middle of the century as fertility declines and today's young people move into middle age.

The two factors that have almost certainly had the greatest influence over human population size are improvements in nutrition and our ability to control infectious diseases. When our ancestors were hunter—gatherers, the human population probably did not exceed 15 million. Development of agriculture allowed the population to grow to around 300 million people 2000 years ago, a number that did not increase in magnitude until the agricultural and industrial revolutions of the latter part of the past millennium. Thus the Haber process for nitrogen fixation, and hence the production of nitrogen fertiliser and vast improvements in agricultural productivity, is among the most important inventions in human history. The industrial revolution also brought about improvements in sanitation—safe disposal of waste and access to clean water—that protected people from exposure to pathogens. Here it is illuminating that in some countries with the fastest growing populations—India and Nigeria, for example—fewer than a third of people have access to what the UNFPA report calls an “improved sanitation facility”. The most recent development in changing population dynamics is immunisation, particularly against childhood diseases, which has saved the lives of incalculable millions from infection.

Few would disagree that human numbers cannot continue growing without limit—at current rates of mortality and fertility, the world population would be an unimaginable 3·5 trillion by 2300. However, attempts to limit fertility by—for example—China's one-child policy, are coercive and unlikely to be sustainable. Recent history shows us that people will limit their own fertility if they have a high degree of confidence that their children will reach adulthood. Although not sufficient on their own, to achieve stable numbers, it is surely essential that all human beings have access to the measures that protect against premature death from infection.