From "Reducing the Risk of Human Extinction", by Jason Matheny. (http://wilsonweb.physics.harvard.edu/pmpmta/Mahoney_extinction.pdf)
Colonizing space sooner, rather than later, could reduce extinction risk (Gott, 1999; Hartmann, 1984; Leslie, 1999), as a species’ survivability is closely related to the extent of its range (Hecht, 2006). Citing, in particular, the threat of new biological weapons, Stephen Hawking has said, "I don’t think the human race will survive the next thousand years,unless we spread into space. There are too many accidents that can befall life on a single planet" (Highfield, 2001). Similarly, NASA Administrator Michael Griffin (2006), recently remarked: "The history of life on Earth is the history of extinction events, and human expansion into the Solar System is, in the end, fundamentally about the survival of the species."
Can anyone point me to existing thought on space colonization from an EA perspective?