Currently it seems that each imperial species is chosen randomly with no accounting for how many times that species may already be chosen. The same Imperials species may often appear 2 or 3 times, while other species don't show up at all. It would be preferable if the game tried to avoid using the same species for multiple empires.
a) Give greater weight to species that have not yet been chosen by human or Ai players. or,
b) Do not repeat species unless the number of empires is greater than the number of imperial species.