m] MALTHUS ON POPULATION 143 



Malthus's Essay on Population* in a French translation, and was 

 impressed like all the world by the importance of the theme. He 

 saw that poverty and misery ensue when a population outgrows its 

 means of support, and believed that multiphcation is checked both 

 . by lack of food and fear of poverty. He knew that there were, 

 and must be, obstacles of one kind or another to the unrestricted 

 increase of a population; and he knew the more subtle fact that 

 a population, after growing to a certain height, oscillates about an 

 unstable level of equilibrium f. 



Malthus had said that a population grows by geometrical pro- 

 gression (as 1, 2, 4, 8) while its means of subsistence tend rather to 

 grow by arithmetical (as 1, 2, 3, 4) — that one adds up while the 

 other multiphesj. A geometrical progression is a natural and a 



* T. R. Malthus, An Essay on the Principle of Population, as it affects the Future 

 Improvement of Society, etc., 1798 (6th ed. 1826; transl. by P. and G. Prevost, 

 Geneva, 1830, 1845). Among the books to which Malthus was most indebted was 

 A Dissertation on the Numbers of Mankind in ancient and modern Times, published 

 anonymously in Edinburgh in 1753, but known to be by Robert Wallace and read 

 by him some years before to the Philosophical Society at Edinburgh. In this 

 remarkable work the writer says (after the manner of Malthus) that mankind 

 naturally increase by successive doubling, and tend to do so thrice in a hundred 

 years. He explains, on the other hand, that "mankind do not actually propagate 

 according to the rule in our tables, or any other constant rule; ^et tables of this 

 nature are not entirely useless, but may serve to shew, how much the increase of 

 mankind is prevented by the various causes which confine their number within 

 such narrow limits." Malthus was also indebted to David Hume's Political 

 Discourse, Of the Populousness of ancient Nations, 1752, a work criticised by Wallace. 

 See also McCulloch's notes to Adam Smith's Wealth of Nations, 1828. 



■f" That the nearest approach to equilibrium in a population is long- continued 

 ebb and flow, a mean level and a tide, was known to Herbert Spencer, and was 

 stated mathematically long afterwards by Vito Volterra. See also Spencer's First 

 Principles, ch. ^22, sect. 173: "Every species of plant or animal is perpetually 

 undergoing a rhythmical variation in number — now from abundance of food and 

 absence of enemies rising above its average, and then by a consequent scarcity 

 of food and abundance of enemies being depressed below its average.. . .Amid 

 these oscillations produced by their conflict, lies that average number of the species 

 at which its expansive tendency ie in equilibrium with surrounding repressive 

 tendencies." Cf. A. J. Lotka, Analytical note on certain rhythmic relations in 

 organic systems, Proc. Nat. Acad. Sci. vi, pp. ^10-415, 1920; but cf. also his Elements 

 of Physical Biology, 1915, p. 90. An analogy, and perhaps a close one, may be found 

 on the Bourse or money market. 



X That a population will soon oiitrun its means of subsistence was a natural 

 assumption in Malthus's day, and in his own thickly populated land. The danger 

 may be postponed and the assumption apparently falsified, as by an Argentine 

 cattle-ranch /or prairie wheat-farm — but only so long as we enjoy world-wide 

 freedom of import and exchange. 



