Actually, I disagree...the basic "model" of the human form is very well
tailored and may be more general than we might suspect. Legs for walking,
probably two because all closed up sideways we present less of a silhouette
for predators, and two legs are more nimble, can slip through narrower places
than three. Arms to lift, and hands to manipulate objects (show me a culture
without a good opposable thumb) required for the birth of technology. Sensors
(eyes/ears/nose) at the very highest part of the body, best for observational
purposes, hunting and the like.

There are zillions of species on Earth, but you rarely seen anything
above spider-level with more than six legs. Now, I'm not saying that it's
impossible to have other forms, not at all...only that the humanoid form may
in fact be far more common than anyone suspects.

jms