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Man didn't suddenly evolve from ape to... human. There were different stages in between the (lets call them) perfect ape and perfect human forms. Now those forms have died, but remains (skeletons) have been found. When put together scientists managed to represent through skeletons, the evolutionary steps. However, through observation they have concluded that the representation is not complete. Because they lack a skeleton which would link two other steps in evolution. That skeleton has yet to be found to this day, and it is why some people (including myself) believe that the skeleton in question doesn't even exist, and that aliens had a hand to play.
Aliens would look like us, not because we look like them. But because of evolution. If they managed to go through space, it must mean that they have oposable thumbs. They most likely have a face, a mouth (they have to eat), two eyes in the front (for depth perception), two hands, two feet... and they are like that because... it's how evolution works. Evolution will not allow needless things to exist. We don't have eyes in the back of our head because we don't really need them. We can hear, we can sense vibrations, there are enough other senses so we don't have eyes in the back of our head. We don't have more than two arms because we don't need more two arms, just like a lion doesn't need more than four legs. We don't have a tail because it's useless to us.
And on an alien planet, where evolution thrives, you won't see a bird with 3 eyes instead of two, a beak with teeth, a fish with feathers, and the list goes on. I can imagine a giant insect, a giant humanoid, but that humanoid, will be humanish, because to reach space travel with a rocketship, you need depth perception, thumbs, hands, mouth, ears.