The passion between the sexes has appeared in every age to be so nearly the same that it may always be considered in algebraic language as a given quantity. The great law of necessity, which prevents population from increasing in any country beyond the food which it can either produce or acquire, is a law so obvious and evident to our understandings that we cannot doubt it. The different modes which nature takes to repress a redundant population do not, indeed, appear to us so certain and regular; but though we cannot always predict the mode, we may with certainty predict the fact. If the proportion of the births to the deaths for a few years indicates an increase of numbers much beyond the proportional increased or acquired food of the country, we may be perfectly certain that, unless an emigration takes place, the deaths will shortly exceed the births, and that the increase which has been observed for a few years cannot be the real average increase of the population of the country. If there were no other depopulating causes, and if the preventive check did not operate very strongly, every country would, without doubt, be subject to periodical plagues and famines. The only true criterion of a real and permanent increase in the population of any country is the increase of the means of subsistence, and even this criterion is subject to some slight variations. Other circumstances being the same, it may be affirmed that countries are populous according to the quantity of human food which they produce or can acquire; and happy according to the liberality with which this food is divided, or the quantity which a day's labour will purchase. This happiness does not depend either upon their being thinly or fully inhabited, upon their poverty or their riches, their youth or age, but on the proportion which the population and the food bear to each other. In modern Europe the positive checks to population prevail less, and the preventive checks more, than in past times, and in the more uncivilised parts of the world, since wars, plagues, acute diseases, and famines have become less frequent. With regard to the preventive checks to population, though it must be acknowledged that the preventive check of moral restraint does not, at present, largely prevail, yet it is becoming more prevalent, and if we consider only the general term, which implies principally a delay of marriage from prudential considerations, it may be considered as the most potent of the checks which in modern Europe keep down the population to the level of the means of subsistence. _III.--Remedies other than Moral Restraint for Evils of Over-population_