The human race would become extinct

Hawking Stephen : theoretical physicist, cosmologist
The human race would become extinct within the next thousand years, unless colonies could be established in space. Humanity faces numerous existential risks, such as war, disease, and climate change.
"In the long term, I am more worried about biology. Nuclear weapons need large facilities, but genetic engineering can be done in a small lab. You can't regulate every lab in the world. The danger is that either by accident or design, we create a virus that destroys us", he wrote.

Highfield, Roger (16 October 2001). "Colonies in space may be only hope, says Hawking". The Telegraph. Retrieved 5 August 2012.