The book An Essay on the Principle of Population was first published anonymously in 1798, [1] but the author was soon identified as Thomas Robert Malthus. The book predicted a grim future, as population would increase geometrically, doubling every 25 years, [2] but food production would only grow arithmetically, which would result in famine and starvation, unless births were controlled.

While it was not the first book on population, it was revised for over 28 years and has been acknowledged as the most influential work of its era. Malthus's book fuelled debate about the size of the population in the Kingdom of Great Britain and contributed to the passing of the Census Act 1800. This Act enabled the holding of a national census in England, Wales and Scotland, starting in 1801 and continuing every ten years to the present. The book's 6th edition (1826) was independently cited as a key influence by both Charles Darwin and Alfred Russel Wallace in developing the theory of natural selection.

A key portion of the book was dedicated to what is now known as Malthus' Iron Law of Population. This name itself is retrospective, based on the iron law of wages, which is the reformulation of Malthus' position by Ferdinand Lassalle, who in turn derived the name from Goethe's "great, eternal iron laws" in Das Goettliche.[3] This theory suggested that growing population rates would contribute to a rising supply of labour that would inevitably lower wages. In essence, Malthus feared that continued population growth would lend itself to poverty and famine.