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Unchecked, population doubles roughly every twenty-five years (1, 2, 4, 8, 16...), while food production can at best be increased by a constant amount each period (1, 2, 3, 4, 5...). Because a multiplying quantity always overtakes an adding one, the gap between mouths and food must widen until something forcibly holds population back to the level subsistence can support.
Population is held to subsistence by two kinds of checks. Preventive checks lower births: people delay or forgo marriage because they foresee they cannot support a family. Positive checks raise deaths through famine, disease, war, bad nutrition and harsh labor, and they fall hardest on the poor. Where one kind of check weakens, the other must rise to compensate.
Giving the poor money under the Poor Laws does not increase the stock of provisions. It only lets more buyers bid for the same food, which pushes up prices and spreads the scarcity more widely. It also encourages people to marry and have children they cannot support, so the policy recreates the very poverty it was meant to relieve.
Suppose Godwin's society of equal property and benevolence were achieved. Abundance would remove the restraints on early marriage, and population would soon outgrow the food supply. Want would then bring back selfishness, violence and eventually private property and inequality as the only workable answers to scarcity, so perfectibility defeats itself.
Reformers blame poverty and vice on corrupt governments and unjust property. This view treats them instead as the result of a fixed biological ratio between the drive to reproduce and the land's capacity to feed people. That shifts the question from which institutions to overthrow to which constraints no institution can escape.
In the North American colonies, land was abundant and food was easy to obtain, and the population doubled in about twenty-five years. This serves as the empirical proof of the power of unchecked human increase. It shows that the slower growth in Europe is not natural moderation but the effect of checks working on a population already pressing against its food supply.