finite world can support only a finite population" and that "freedom to breed will bring ruin to all." The Club of Rome published a book entitled The Limits to Growth in 1972. The report and the organisation soon became central to the neo-Malthusian revival. Paul R. Ehrlich has been one of the most prominent neo-Malthusians since the publication of The Population Bomb in 1968. Leading ecological economist Herman Daly has acknowledged the influence of Malthus on his concept of a steady-state economy. Other prominent Malthusians include the Paddock brothers, authors of Famine 1975! America's Decision: Who Will Survive? The neo-Malthusian revival has drawn criticism from writers who claim the Malthusian warnings were overstated or premature because the green revolution has brought substantial increases in food production and will be able to keep up with continued population growth. Julian Simon, a cornucopian, has written that contrary to neo-Malthusian theory, Earth's "carrying capacity" is essentially limitless. Simon argues not that there is an infinite physical amount of, say, copper, but for human purposes that amount should be treated as infinite because it is not bounded or limited in any economic sense, because: 1) known reserves are of uncertain quantity 2) New reserves may become available, either through discovery or via the development of new extraction techniques 3) recycling 4) more efficient utilization of existing reserves (e.g., "It takes much less copper now to pass a given message than a hundred years ago." [The Ultimate Resource 2, 1996, footnote, p. 62]) 5) development of economic equivalents, e.g., optic fibre in the case of copper for telecommunications. Responding to Simon, Al Bartlett reiterates the potential of population growth as an exponential (or as expressed by Malthus, "geometrical") curve to outstrip both natural resources and human ingenuity. Bartlett writes and lectures particularly on energy supplies, and describes the "inability to understand the exponential function" as the "greatest shortcoming of the human race". Prominent neo-Malthusians such as Paul Ehrlich maintain that ultimately, population growth on Earth is still too high, and will eventually lead to a serious crisis. The 2007–2008 world food price crisis inspired further Malthusian arguments regarding the prospects for global food supply. From approximately 2004 to 2011, concerns about "peak oil" and other forms of resource depletion became widespread in the United States, and motivated a large if short-lived subculture of neo-Malthusian "peakists". A United Nations Food and Agriculture Organization study conducted in