Population regime· The columns of time

Industrial growth

1800 → 1950

Between 1800 and 1950, the first phase of the demographic transition, world population went from about one billion to 2.5 billion.

Regime corresponding to the first phase of the demographic transition. World population moves from about one billion inhabitants in 1800 to 2.5 billion in 1950, a multiplication by two and a half in a century and a half, where the first billion had required three hundred thousand years.

What the evidence shows

The determining factor is not an increase in births but a decrease in deaths, principally infant deaths. Sanitation, then vaccination, then antibiotics each removed a substantial share of a mortality until then held to be inevitable. The order of these phenomena constitutes the mechanism of the demographic transition: mortality falls first, fertility follows with delay, and it is the interval between the two curves that produces growth. The band represents a world total and not its composition: between 1800 and 1950, a single curve covers regions where that interval was already closing and others where it was only beginning to open.

Bounds and conventions

The 1800 limit is a historiographical convention and not a measurement, and national censuses become general only during the nineteenth century. Earlier figures rest on tax rolls, parish registers and reconstructions, and carry ranges wide enough that the shape of the curve is better established than any of its individual values.