Ralph Waldo Emerson, Robert Ernest Spiller, Alfred Riggs Ferguson, Joseph Slater, Jean Ferguson Carr (1971). “The Collected Works of Ralph Waldo Emerson: Nature, addresses, and lectures”, p.9, Harvard University Press
Immanuel Wallerstein (2011). “The Modern World-System I: Capitalist Agriculture and the Origins of the European World-Economy in the Sixteenth Century, With a New Prologue”, p.357, Univ of California Press
"The Coming Technological Singularity: How to Survive in the Post-Human Era". Vernor Vinge's remarks presented at the VISION-21 Symposium sponsored by NASA Lewis Research Center and the Ohio Aerospace Institute, edoras.sdsu.edu. March 30-31, 1993.