reply to post by symmetricAvenger
I have to say that I have come up with a working theory that supports your hypothesis.
I believe that there are enough conditions for sentient, space traveling life, that would demand certain body features.
For example: while we can perhaps imagine dolphins evolving human like intelligence, we will never see a creature that live under water discover fire.
And there is no chemical reaction that can be accesses with the same ease as fire, but that occurs under water.
Fire, as we know, was an important step in our development of technology.
The same can be said for the development of bipedal transportation. Bipedal transport allowed the upper extremities to become available for other
uses, like tool making and food gathering, etc.
There seems to be a very strong preference for symmetry in nature, two eyes provide depth perception, and the evolution of light detecting organs such
as eyes happens pretty much everywhere here on earth.
Finally, evolution prefers economy: creatures that have so many extra extremities may seem to have an advantage at first, but they have higher
metabolic requirements and therefore, the creature with the least limbs but still enough for survival, has an advantage.
These types of mechanisms that are at play in an otherwise seemingly random process (evolution) are what people often ignore when proposing the
infinite random possibilities they can imagine for life.
I am pretty sure that given enough examples of sentient life, if that data ever became widely available, scientists would be perfectly able to
backwards rationalize why it makes perfect sense for whatever similarities and differences they find in other creatures, even if those creatures all
turn out to be humanoid.
Besides, another good explanation for humanoid "aliens" could just as well be that these beings are the results of genetic experiments on humans
(and therefore originate here on earth.) It is pretty much a given that genetic engineering done by the military must be ahead of mainstream science,
just as every other engineering aspect. We can only begin to imagine how far they've come along in making, say, a humanoid that doesn't need to eat,
but can pilot a vehicle for days at a time on nothing but sunlight. If it has a military application, they have at least looked into whether it's
possible and made some attempts.