Since population outruns food supply, dire human consequences naturally follow. Food supply, as a check upon population, operates harshly; it is but representative of an entire series of rigorous natural, or positive, checks upon population. In this list there are unwholesome occupations; forms of severe labor; extreme poverty; damp and wretched housing conditions; diseases, epidemics, plagues, poor nursing; intestine commotion, martial law, civil war; wars of all forms; excesses of all kinds.[XII-5] These positive checks upon population are the results of two main causes, namely, vice and misery. As a result of the operation of these factors, population is being continually cut down and kept near the mere subsistence plane. Malthus pointed out another check upon population, the preventive. The fear of falling into poverty causes many young people to postpone marriage until they can safely marry--economically. This check so far as voluntary is peculiar to man and, to the extent that it is not followed by irregular sex gratification, is prudential. The actual pressure of population upon food supply, or the fear of this impingement, prevents people from marrying earlier than they do and from reproducing their kind faster than they would do otherwise. This pressure, or the fear of it, cuts down the marriage rate in times of economic depression. But let prosperity come and the marriage rate leaps upward, especially among the poorer classes. The positive and preventive checks upon population hold a definite relation to each other. “In every country where the whole of the procreative power cannot be called into action, the preventive and the positive checks must vary inversely as each other.”[XII-6] That is to say, when positive checks, such as famine and war, slay large numbers of people, moral restraint is diminished and the population numbers rapidly increase. When the preventive check expresses itself strongly, the population is kept down numerically, and positive checks, such as famine or even war, are defeated. Malthus attempted to establish three propositions: (1) The limitation of population by the restriction of the means of subsistence. (2) The invariable increase of population whenever the means of subsistence increase, unless prevented by powerful checks. (3) The factors which keep population on a level with the means of subsistence are all resolvable into three: moral restraint, vice, and misery.[XII-7] No one can gainsay the importance or the seriousness of the problem of population. Plato wrestled with it, and urged that procreation when it goes on too fast or too slow should be regulated by the state--through a proper distribution of marks of ignominy or of honor. The number of marriages should be determined by the magistrates. Aristotle suggested that the ages of marriage for both sexes should be regulated; he even advocated the regulation of the number of children for each marriage. Additional children should be aborted.