[cmdrfred]

Or they fail to thrive like humans have. Early humans were few in number and might have nearly died out a few times. We just got lucky.

I've also wondered how a race without something like a hand ever gets around to making complex tools with multiple moving parts. If Dolphins had twice the brain power that they do now, would they be able to build anything? The intelligence of other races may simply fail to be expressed in any way that is noticeable once they are gone. Hell dinosaurs might of been smarter than us and simply unable to use and create tools.

[zebrafish]

I don't think you're allowed to pose the dolphin question. If we assume that dolphins and humans have a common ancestor and that the dolphin branch ever had a need for using tools to sustain their species, over time enough random permutations of specific genes would have selected those dolphins which had appendages capable of aiding in the use of tools. As it turns out, they did not need to have hand like appendages to survive and thus apes have hands and ocean mammals do not.

Given the constraints (earth located in our universe) of the probability space of physical interactions which produce life, I believe that our current state is the only possible state.