For 10 points, give this quantity, which is currently approximately equal to 7.5 billion.
William Ophuls proposed a "steady-state philosophy" to reduce this quantity in response to Herman Kahn's suggestion that changes in this quantity are not "carcinogenic" but rather benevolent. A four-stage model that describes how this quantity changes over time is the subject of Warren Thompson's "transition" theory. The idea that increasing this quantity has been beneficial is the mainstay of so-called "cornucopian" theses and is central to the book The Ultimate Resource by Julian (*) Simon. Paul Ehrlich suggested that the rate of growth of this quantity should be zero in a book that refers to it as a "bomb." The idea that this quantity grows geometrically while resource production only grows arithmetically is the basis for the "Malthusian catastrophe." For 10 points, give this quantity, which is currently approximately equal to 7.5 billion.
William Ophuls proposed a "steady-state philosophy" to reduce this quantity in response to Herman Kahn's suggestion that changes in this quantity are not "carcinogenic" but rather benevolent.
human population [accept reasonable equivalents, such as the number of people; prompt on population] 