Originally Posted by afan
The answer is a question....Why not?
Because evolution is largely a random process, based on whichever species have to be lucky enough to have whatever mutations allow them to thrive. Even assuming that conditions on Krypton are very similar to those on earth, the likelihood of all the different mutations allowing a single species to dominate being the same as those on earth are very, very small. In Star Trek, they explained this by having a primitive humanoid species direct evolution on various planets to be similar to their own, but even then minor differences occurred due to varying conditions. \S/uperman's explanation could work. An idea I had would be to make Krypton start out as a sort of intergalactic zoo, with the Kryptonians being descendants of prehistoric hominids who eventually come to be more advanced than their counterparts on earth.