The biggest advantage to the humanoid body type is that it's well-built for tool manipulation (hands with opposable thumbs) and that two feet is, overall, more efficient than four or more feet for movement (humans are some of the best endurance runners in the entire animal kingdom). Binocular vision is also a plus (though not a must), as is putting the head atop the shoulders, where it can observe more. It also make sense for eyes, ears, and other sensory organs to be close to the brain, so that there is as little delay in reaction as possible.
So there are definitely advantages to the humanoid body type that shouldn't be overlooked. That doesn't preclude the possibility however of a different, but equally useful body type evolving or a species evolving whose body is not as optimally designed for tool-using and what we would understand as civilization but who are nonetheless sapient (hanar are a good example of this).
Fact is this, though, the most successful alien species (presuming they exist, which I believe they do) will almost certainly have a body type roughly anagolous (roughly being the operative word here) to humans. Let's imagine, for instance that bottlenose dolphins are (as many would claim) sapient. Regardless of how advanced they may be mentally, dolphins are incapable of dominating the planet to the same extent that humans are, simply because they aren't as physically well-suited for the kind of behavior we associated with civilization. Naturally, this isn't to say that dolphins aren't well-adapted to their own environment: an unaided human couldn't live the way a dolphin does anymore than an unaided dolphin could live like a human. But the fact is, our physical capacities lend well to things like fire-making, writing, industrial development, and space flight.
Just my 2 cents on the matter.
Modifié par Nivenus, 16 avril 2010 - 07:06 .