"Well, if that's what astrobiologists say they might do better to talk to palaeontologists who have some insight into the mechanics of life."

They have, Sugarfoot. As I have said a number of times here, the field of astrobiology includes all scientific disciplines (including paleontology), and they all have an input into any new theory that someone comes up with. The folks involved in this field are anything but lightweights. Don't underestimate them. This is a serious field of study.

I'm not trying to claim that bilateral symmetry, four limbs, skeletal structure, two eyes, two ears, etc., is the only possible model for intelligent aliens. What I am saying is a response to someone up-thread trying to claim that there are no intelligent extraterrestrials, and even if the impossible were to occur, they would not look even remotely humanoid.

This is not what exobiologists/astrobiologists maintain. They don't say that this is the only possible model by any means, but the idea that no alien species would ever appear humanoid is something they reject, along with the idea that alien species would all look like they came from Central Casting and were equipped by the make-up department with pointy ears or a turtle shell on their foreheads.

It's hard to imagine a sponge-like creature affixed to a rock at the bottom on an ocean and surviving on passing plankton needing to evolve much in the way of intelligence. I've spent a lot of time at various beaches, but I've never had a clam emerge from the sand and say, "Take me to your leader!"

To evolve intelligence (fundamentally, a survival mechanism), a creature needs to be, among other things, mobile—and challenged in some way, so that the fittest of the species (those which survive whatever the challenge is) go on to breed even more intelligent members of the species.

Basic. Whether on Earth or on a planet at the edge of the visible universe.

Don Firth

P. S. By the way, do not make the mistake of underestimating the speculations of some science fiction writers. Many of the best are solidly grounded scientists. Arthur C. Clarke (in non-fiction articles) has hypothesized a number of different models for intelligent aliens, from very exotic on non-earthlike planets to very humanoid (but quite different) on terrestrial planets. Orson Scott Card is also a rather ingenious (but solidly science-based) inventor of alien species. It's possible to hypothesize a humanoid appearing species which is very un-humanoid in its other aspects.

Rationally, one cannot rule out anything that is not outright scientifically impossible. And the fact that WE exist PROVES that humanoid is a viable form on planets with earthlike or near-earthlike characteristics.

The future may hold some amazing surprises.

Or not.