Neo-Malthusians argued that, for a given species and situation, population tends to grow until it encounters a critical resource limit or controlling factor, whereupon there is a gradual or sudden, limited or catastrophic decline in numbers, or a shift to a cyclic boom-and-bust pattern. Neo-Malthusians saw population growth as the primary cause for concern, although a few also focused on the growing threat from ‘careless technology’ (Farvar and Milton, 1972).