I was discussing with my Mom the other day how there's an large amount of illegitimacy in movies and books when depicting aliens. For some reason, as a species, we have assumed that if we were to come across foreign life, they would be similar to us in shape and ideas.
Let me rephrase this: from an evolutionary standpoint, there is no reason that aliens would be bipedal, have any limbs whatsoever, or even have any recognizable features for that matter. The only reason that humans share these features with other earthly critters is because of a common ancestor. A creature from a different planet would not have that evolutionary ancestor in common, and so it most likely would not have any similar traits. It could even very well be incomprehensible to us, beyond our imaginations.
Another point to consider is that our concept of life could be different from the existence of something else. What is life as we know it? I don't mean to be philosophical here; I mean it literally. Something that is considered alive by us is made up of organic and cellular matter. Who is to say that something that we would perceive as an existing being would be made up of similar materials? There is no reason for it. If there is life of some sort in the universe, I don't think it will come forth in the form of tiny green men.