Robert Silverberg 
Seed of Earth 

The computer had chosen them – a small cross-section of humanity to serve Mankind’s Destiny. Out of seven billion people on Earth mechanical chance had selected them as involuntary colonists on an unknown planet. In seven days they would be on their way, on a sink-or-swim mission to a lonely world beyond the limits of the Solar System.It was a summons each had privately dreaded, yet always been prepared for. But no one had prepared them for the vicious attacks of sinister aliens . . .