Why the typical "alien" looks remarkably human, all things considered? i.e. it has two arms, two legs, two forward facing eyes, a set of nostrils between those eyes, fingers, similar looking joints, walks upright, ect. What I'm getting at is that if these creatures are from a distant planet, what are the odds life evolved on that planet to produce anything remotely close to the above mentioned stereotypical alien? Very low, in my opinion...
The same reason all of our gods look like us: we anthropomorphize our myths and fantasies. We project our own qualities on the mysterious in order to make sense of it. One need only look at the anthropomorphic habits of cartoons to see good example of this: Sponge Bob, Wile E. Coyote, etc. Cultures have been variously applying animism, totemism and the like to animals, objects and even the weather for centuries, creating deities, creatures and spirits that have human qualities and characteristics. Be it a volcano, a jaguar, a jackal, or a god of thunder swinging a hammer, they all have features that mimic our own: hunger, lust, bipedalism, tool use, etc. There's no reason to expect that wouldn't also continue this projection on space aliens as we move into the space age and come to the realization that the universe is a big place and there is likely to be a multitude of life out there somewhere. There's also the effect of pareidolia where humans see an object or pattern and recognize human characteristics in it. The face on Mars is a good example. So are the various shapes of Virgin Marys on sandwiches and tacos or the spillways of highway underpasses (calcification and discoloration from water dripping the wall from a drain). We anthropomorphize unknown aerial phenomena (headlights on a low cloud on a dark night) by expecting an intelligence to be flying it since its in the sky. The intelligence behind the light is actually on the ground, yet the observer is unaware since this sort of observation has never occurred to him/her. The subsequent sighting of the shadows of deer in a field where the light seemed to "land" brings about the expectation of these "intelligent" beings. We then project or anthropomorphize ourselves on the shapes -our brains filling in the patterns with what we expect to see: bipedal forms, standing upright. But its dark. We don't really see the scene in a good light -the brain is making up the difference.
People could have buggered off to some other planet and evolved differently, and then decided to come back for a visit.
2 eyes gives us a 3D view of the world and an ability to judge distance. 2 ears give stereo and distance hearing. A nose so we don't chock while breathing through our mouth while eating or drinking. Skin is to protect our innards as well as holding them together, with the help of our skeleton. Hair to a lesser degree is protection (a leftover from fur). Feet ready for walking on (upright so we can have a larger brain) and ass for sitting on. Reproductive organs, wombs, etc. The needs are basically the same for every intelligent being. There could be alien imperatives on evolution from different atmospheric pressure, radiations, water and so on. There are other routes that could be taken, like tentacles instead of arms but why bother if you have a skeleton? Basically, almost all aliens will look like us rather than BEM's, monsters, etc. What really annoyed me is Star Trek (notably DS9) where all aliens except humans have weird patterns and shapes to their heads. WHY? What would make this happen?
