The immediate cause of the increase of population is the excess of the births above deaths; and the rate of increase, or the period of doubling, depends upon the proportion which the excess of the births above the deaths bears to the population.
Thomas MalthusPopulation, when unchecked, goes on doubling itself every 25 years or increases in a geometrical ratio.
Thomas MalthusThe natural inequality of the two powers of population and of production in the earth, and that great law of our nature which must constantly keep their efforts equal, form the great difficulty that to me appears insurmountable in the way to the perfectibility of society.
Thomas Malthus