"For the survival of the species"

World-renowned physicist Stephen Hawking:

"It is important for the human race to spread out into space for the survival of the species," Hawking said. "Life on Earth is at the ever-increasing risk of being wiped out by a disaster, such as sudden global warming, nuclear war, a genetically engineered virus or other dangers we have not yet thought of."

So sad that the last two known causes (and probably the unknown too) would be man-made.

Man really is the only animal that kills his own.