I was reading through my copy of Making Contact by Bill Fawcett and found a chapter expaining why Extraterrestrials would in fact have a humanoid appearance. Now I don't mean to say ALL aliens look like us just some.
The reasonings are here and taken from the book from pgs. 205 and 206
Review of Beginning Concepts:
* Nature is uniform. The phyiscal and chemical processes in our solar system are the same in all.
*The chemestry of life is the same everywhere. The critical elements are available everywhere. Also the amino acids and basic molecules can be found in gas clouds, metorites, comets, and planet cores.
* The forces that assemble proteins and DNA are available everywhere. Ultraviolet radiation, volcanic heat, and lightning just like that which assembled our physical makeup are common place on nascent Earths.
* The environments that produce life are very Earth-like. We could likely walk, swim, and breathe on most worlds which produced life. Other Earth-like planets would have masses between one-half and two-and-a-half times our Earth.
The following can be found on pgs. 212-214
The Macro Structure of ETIs:
* Belong to the animal kingdom.
* Dwell on land.
* Be relatively large in size.
* Have a tube-shaped digestive tract that worked one way.
* Have gas-exchange system that worked two ways.
* Have a head with a large brain, mouth, eyes, ears and major sense organs protected by a skull.
* Have an internal skeletal system.
* Have four limbs. Two of which would be adapted to be manipulating appendages.
* The head would have a food-intake oriface, two light sensing organs, a secondary organ for air intake, odor sening organs, along with bilateral sound sensors. These would be located close to the brain.
* Major sensory organs would be above the mouth so as not to lead to problems while feeding.
* The secondary air intake would be located close to the mouth so one tube could serve both and so food could be found and then checked before eating.
* The light sensing organs would be located in the front and focusable.
* The sound sensing organs would be located laterally.
* A system of branching scaled tubes would make use of pumped water to deliver nutrients from the food processing system to the body's cells and a separate set of tubes would bring waste back to the system.
* A torso large in size would have within the food-processing system and aditional mantinence organs.
* The body's internal skeletal structure would strong yet flexible and mobile. Positioned in a generally upright possition, allowing freedom of manually dexterous appendages.
* There would be two genders.
* Sizes and shape of the body and it's parts would vary.
* Pigmentations and textures of eyes skin etc. would be decided raditation conditions and body part functions.
* Mouth parts such as teeth, beaks, mandibles etc. would be connected with diet.
* Number of digits on fore appendages would likely number between three and five. While hind appendages would vary more greatly or possible have none.
* Total number of small bones, joints, and muscles would vary along with angles of joints. But this would have limited variability in the number of designs of major joints and levering designs.
* Reproductive organs would differ in size and shape with likely location of the torso. A wide range of outward differences between genders from none to marked levels would also exist.
* Internal organs would vary in structure and placement. Decided by factors like diet, gas exchance etc.
Such body structures would most likely be in those lifeforms that came about as a reseult of evolution. If genetic engineering is involved then the only limit would be on the creator's knowlage, ability and desire. However at present we humans cannot produce specimens at a viable level for continued life.
In addition there are two things also worthy of note:
1. The contrary theorists have no evidence to back up their claims.
2. The converging theorists have an entire planet for theirs.
In summation it is my belief that the information gives a reasonable amount of evidence for extraterrestrials to have a form similar to humans. This would be in line with the descriptions of the Greys/Zeta Reticulans, Reptoids, and Pleidans/Pejarens.