Physicist Stephen Hawking, who recently said humans should avoid seeking out aliens because they might colonise our planet if they noticed us, has now warned that mankind must colonise other planets or face extinction.

"I believe that the long-term future of the human race must be in space," Hawking tells BigThink.com. "It will be difficult enough to avoid disaster on planet Earth in the next hundred years, let alone the next thousand, or million.

"There have been a number of times in the past when survival has been a question of touch and go. The Cuban missile crisis in 1963 is one of these. The frequency of such occasions is likely to increase in the future."

It's not just nuclear oblivion we have to fear though. Thanks to our selfish genes, Hawking appears to believe it is inevitable that we will destroy the earth.

"Our genetic code carries selfish and aggressive instincts that were a survival advantage in the past. It will be difficult enough to avoid disaster in the next 100 years let alone the next thousand or a million." Overpopulation or runaway global warming for instance.

Even if we can go against our animal instincts and preserve the earth, the sun will have scorched our planet into a dry ball of rock within just 1bn years, according to scientists.

Hawking thinks we should be able to develop interstellar space flight long before then: "I am an optimist," he claims, surprisingly. "If we can avoid disaster for the next two centuries our species should be safe as we spread into space."

Hawking: mankind must colonise other worlds or face extinction