For the sake of argument, let us grant you and Conway Morris your main point: life on other planets would take the same course of evolution, cognition and culture would be roughly similar to what we know, etc. Let's say you're right. Does it follow that Pandora is a probable planet ? No !

It took billions of years for Earth to become Pandora-like. The chances for an Earth-explorer landing on the planet at any moment in that great length of time, and finding Earth Pandora-like (with multicellular life, trees, flowers, animals, cognition, culture, etc.), are exceedingly small. If the universe had 10000 planets exactly like Earth, the chances of one of these planets being Pandora-like right now would still be exceedingly small.

I fully agree with you. My point was the following: If humans were to discover an intelligent life, it would probably be very similar to us. That does not imply that the evolution of intelligent life is probable. Actually, Conway Morris, who advocates evolutionary convergence, thinks that we are alone in the universe (cf the subtitle of his book: Inevitable humans in a lonely universe).

And as you say, even if the universe contains billions of billions of solar systems, most of them are too far away in time and space to make a meeting with intelligent aliens more than improbable.

In the improbable case that we would find intelligent life somewhere in the Universe, would it not escape our perception of it if it did not show a lot of features in common with what we now mentally represent as INTELLIGENT?

No surprise those blue guys and dolls have, well, all it takes to make the film watchable and the story intelligible (and the images at least minimally attractive). People try very hard to invent new worlds and species - yet they all end up looking very much the same. That is why (at least to some high-brow readers) many science-fiction books and films seem all eerily similar. Despite the authors' best efforts, the plots turn around warfare, people who wage wars are organised in armies or army-like states, people wear uniforms, etc etc. Was it really worth it travelling through galaxies to discover some purple-skinned version of the US Army?

Interestingly, some high-brow authors too have tried, with better success of course, to imagine worlds really different from our own. See for instance Borges's famous Tlon Uqbar Orbis Tertius, a country where idealism is true - things only exist inasmuch as people think about them. But, no surprise there - the account stops after a few pages. There is just no way to spin any kind of story in a world like that.

Which leads us to the more interesting and anthropological question, What exactly are those limits on imagination? I think we should pursue Nicolas's questions further. For instance, as he notes, cognition and behavior in the blue-folks film are diasppointingly similar to what we (Western, humans) expect. But I would bet (having not seen the film) that they also have ostensive gaze, gestures rythmically coordinated with speech, turn-taking in conversations, and another million features that happen to be special to our species - and so familiar that we do not even think that they may be different elsewhere.

There is no general "cognition and culture" study of the limits of imagination, except the work done by Justin Barrett (seehttp://www.icea.ox.ac.uk/about-us/staff/dr-justin-barrett/dr-justin-barrett-publications/) and a few others on religious concepts. Despite the fact that there is no principled limit to imagining gods and spirits - contrary to tigers and trees, they are not actually around to constrain your ideas about them - supernatural entities turn out to be depressingly similar non-physical agents with slightly counter-intuitive physical or biological properties, but minds similar to our intuitive expectations about people.

These are not solid limits to imagination. We can, and sometimes do, imagine beings and objects that really violate our intuitive expectations. But this takes more effort than imagining human-like spirits. It also takes more effort to convey those thoughts, to recall them, to explain them, etc. Which creates "cultural attractors" like spirits and gods.

Wittgenstein was wrong about this (as about everything else, but that will be the topic of another post). We are not like flies in a bottle, incapable of overcoming our intuitive expectations. The shackles of intuitive ontologies are elastic - the further away from rest position you want to go, the more energy it takes, and the faster your mind will snap back to its entrenched expectations when the effort is relaxed. The amount of effort that will be expended to sustain a particular fiction is of course dependent on the cognitive effects of engaging in that pretence.

Which predicts all sorts of properties of culturally successful artistic traditions - more grants are needed!