is the condition which governs the growth of the population of all
animal species, and, as we have already said, of the savages and
barbarians among the human species. But among civilized men who have
attempted the control of physical nature, and to some extent even the
control of human nature, many other factors enter in to influence both
birth rate and death rate, and so the growth of the population.

Nevertheless, many social thinkers of the past have conceived, as has
already been said, that the growth of population might be reduced to
very simple and definite laws. Among the first who proposed laws
governing population was an English economist, Thomas Robert Malthus,
whose active career coincides with the first quarter of the nineteenth
century. In 1798 Malthus put forth a little book which he entitled _An
Essay on the Principle of Population as it affects the future
improvement of society_. This essay went through numerous editions
and revisions, and in it Malthus elaborated his famous economic theory
of the growth of population. Inasmuch as this theory of Malthus has been
the storm center of sociological and economic writers for the past one
hundred years, it is worth our while to note very briefly what Malthus's
theory was, and why it is inadequate as a scientific statement of the
laws governing the growth of population.

_Malthus's Theory of Population._ In the first edition of his essay
Malthus contended that population tends to increase in geometric ratio,
while food at best will increase only in arithmetical ratio; and that
this means that constant discrepancies between population and food
supply would appear, with the result that population would have to be
cut down to food supply. Later Malthus saw how crude this statement of
his theory was and abandoned any attempt at mathematical statement,
presenting substantially the following theory: (1) Population is