 Even though Human Head had a pretty open canvas when starting  development of Prey, there were a few elements from the original  Prey design document they were not allowed to remove from the game.  The game had to have a Native American who had been unhappy with his  heritage as a protagonist. This person had to be abducted by aliens,  and that protagonist had to use his heritage as a weapon against a  technically superior alien species. Also, since portals had been  such an important part of the original Prey, they also had to appear  in the game.