Either Stone Age man was a technological wizard, who carefully removed his technological achievements so as not to upset his inferior progeny, or our population dwindled from a once astronomical size to the mere three billions of today.

Von Foerster, Mora and Amiot (1961) "Population Density and Growth". in: Science, Vol 133, 16 June 1961, pp. 1932-37 as cited in: Stuart A. Umpleby (2001) "Heinz von Foerster (1911 - 2002)"