In 1798 Thomas Malthus (1798, 1801) published his theory of the relationship between social action and the processes of nature. He argued that human population grows geometrically but agricultural production, or more generally the means of subsistence, only grows arithmetically. Thus population increases beyond the means to sustain it, the excess population that cannot be sustained by the natural environment is eliminated, and then the population and the means of subsistence grow once again at their respective rates until their interaction produces the next crisis. Boom and bust cycles are, according to this theory, written into the relationship between humans and their natural environment. Malthus concluded that, although population growth could be limited by "preventive" checks (birth control, infanticide) and by "moral restraint" (sexual abstinence), it is usually brought back to equilibrium by "positive" checks (famine, epidemics, and war). He arrived at this conclusion because he believed that sexual abstinence was improbable and, like many Protestant ministers of that age, that birth control was morally repugnant. The famines in Ireland in the 1700s and early and middle 1800s seemed to support his theory.