The growth of the human population

A natural population grows in an S-shaped curve, but the growth curve of the human population is J-shaped: the human population is still in the phase of rapid growth.

t	0	0.5	1	1.5	2	2.5	3	3.5	4	4.5	5	5.5	6	6.5	7	7.5	8	8.5	9	9.5	10
N	0.3	0.36	0.43	0.51	0.62	0.74	0.88	1.06	1.27	1.52	1.81	2.17	2.6	3.11	3.73	4.46	5.34	6.4	7.66	9.17	10.98

Figure 15.5 — the human population growth curve: slow growth (1), then ever-faster growth (2) with no levelling off.

It took about 300,000 years for the world's human population to reach one billion. It reached two billion 130 years later, three billion 30 years after that, and four billion only 15 years later. The two main reasons for this rapid growth are a rising birth rate and a falling death rate, brought about by technological progress, advances in medicine and increased food production.

year (AD)	1	1804	1927	1959	1974	1987	1999	2013
billions	0.25	1	2	3	4	5	6	7

Figure 15.6 — the growth of the world's human population from AD 1 to 2013, in billions.

Assignment 15.2 — worked

Use the graph to predict how long it will take for the world population of 2013 to double.

Doubling 7 billion means reaching 14 billion — 7 billion more.

On the graph, each recent billion took about 12–15 years (1974 → 1987 → 1999 → 2013).

7 × 12 to 7 × 15 ≈ 85 to 105 years.

If growth kept its recent pace, the population would double in roughly 90–100 years, near the end of this century.

A prediction, not a certainty

Reading a trend off a graph assumes it continues. In fact birth rates are falling in many countries, and experts expect the human population to slow down and level off — to turn its J into an S.

The human curve is a J

Human numbers are still growing fast — from 1 billion in 1804 to 7 billion in 2013 — because birth rates rose and death rates fell.