1. See, for example, Carl Sagan, The Cosmic Connection (New York: Dell, 1973);
2. Carl Sagan, Cosmos (New York: Random House, 1980).
3. R. T. Rood and J. S. Trefil, Are We Alone? (New York: Scribners’, 1982);
4. M. H. Hart and B. Zuckerman, eds., Extraterrestrials: Where Are They? (New York: Pergamon, 1982).
5. For a very brief account of these early writings, see Lewis White Beck, “Extraterrestrial Intelligent Life,” in Edward Regis, Jr., ed., Extraterrestrials: Science and Alien Intelligence (Cambridge, UK: Cambridge University Press, 1985), 3–18; a longer history is given in