The issue of overpopulation has been debated since at least 1786 when economist Thomas Malthus published his theory that the growth of the population will always outpace the growth in the food supply. This theory is known as Malthusianism. Malthus viewed the problem as an over-stretching of resources. Today's thinkers tend to give greater importance to the ethical and efficient distribution of resources. In any case, population trends are complex and their results are subject to debate. The population of the Earth has indisputably risen dramatically in the past 70 years, from under three billion in 1950 to nearly eight billion now. But birth rates have declined sharply in developed nations during the same period.