The Seed of Earth/Next Stop the Stars

Blurb:

(from Ace 1962)

In a dark cave, on a cold planet, in a distant galaxy, four Earthmen sat and pondered the chance that had sent them there. The Computer had picked them to carry human civilization out beyond the limits of the Solar System. They were to be pioneers of a virgin world.

Do Your Share for Mankind's Destiny read the slogan back on Earth. But Mankind's Destiny had not prepared them for the onslaught of the vicious aliens.

Four humans, alone in a cave, waiting for the outburst that would hurl them at each others' throats, feeling the alien eyes observing their every action, and knowing that whatever they did would determine the future of their entire colony.