no. it's not inconsistent. the movie splatters various visuals clues as to humans current state over and over. They learned to carve weapons from bones, use utensils, make fire. Now they're struggling just to piss in outer space, they became, once again monkeys. The first part sets the tone for the rest of the movie: man's need to evolve. The second half shows they suck at living in space and the need to step it up to the final evolutionary form in order to live in space.