Today the human race is a single twig on the tree of life, a single species on a single planet. Our condition can thus only be described as extremely fragile, endangered by forces of nature currently beyond our control, our own mistakes, and other branches of the wildly blossoming tree itself. Looked at this way, we can then pose the question of the future of humanity on Earth, in the solar system, and in the galaxy from the standpoint of both evolutionary biology and human nature. The conclusion is straightforward: Our choice is to grow, branch, spread and develop, or stagnate and die. - Robert Zubrin, Entering Space, 1999
In time, a Martian colony would grow to the point of being self-
sustaining. When this stage was reached, humanity would have a precious
insurance policy against catastrophe at home. During the next millennium
there is a significant chance that civilization on Earth will be destroyed
by an asteroid, a killer plague or a global war. A Martian colony could keep
the flame of civilization and culture alive until Earth could be reverse-
colonized from Mars. - Paul Davies, The New York Times,
2004