....I’ll address the different aspects of the science in sections.


From a visual perspective, Avatar’s Pandora is breathtaking. While
most movies have only hinted at the exotic nature of their worlds with
an establishing matte painting or two, here Cameron takes us on an
elaborate three-dimensional tour though various habitats, from the
treetops to the forest floor. He’s created a whole ecosystem, from
semi-intelligent trees to giant land and air creatures. Most seem
inter-related via symbiotic relationships. In fact, Cameron has taken
the Gaia hypothesis, that the biosphere of the Earth is itself a kind
of living entity, and sexed it up – the biosphere of Pandora is
essentially a god, and it’s networked! Creatures can plug into each
other via what amounts to USB hair and fiber optic roots. While some
of these ideas are not without their faults (see below), Cameron gets
points for creativity – this is true science fiction, not space opera.

I do have one minor complaint, that given their networking abilities,
the Na’vi should not be so technologically inferior to the humans. On
Earth, the largest barrier to technological progression was that
information that existed in the brains of primitive humans could not
be easily shared or preserved. As soon as writing was developed,
suddenly it was possible to store information outside of the brain,
and record and build upon knowledge. The knowledge available to a
human or tribe went from one brain’s worth (and a minimal amount of
oral tradition), to thousands, and ultimately billions of brains’
worth. The result was a technological and social explosion. Hominids
have had technology like spears for about half a million years, but
only 7,000 years after the development of writing we had left the
planet. And the sharing of knowledge is still undergoing a revolution
with the development of the internet. Now we have instantaneous
access to the combined knowledge of the entire history of humanity.

Since the Na’vi have had the ability to download information and share
it in a massive network for long periods of time (evolutionary
timescales), they should be way ahead of us in terms of technological
development. Still, I have to give Cameron a pass here. It is
thematically necessary that the Na’vi are technologically primitive,
and their root-network is necessary to the plot. Maybe you could say
that they could have evolved more technology, but they don’t need it
or want it. Still, that reeks of the “Noble savage” idea, and I have
to agree with Stephen Pinker that that is a bunch of hoo-ha.

But my major complaint from an evolutionary standpoint is that there
is no way in hell that life on Pandora would evolve to look so similar
to Earth life: there are humanoids, space horseys, hammerhead
rhinoceri, and pseudo-pterodactyl beasties. And to make it worse,
they have DNA, and the DNA is close enough to our own that Na’vi and
human DNA can be combined! Again, I have to give Cameron a pass.
First, it is easier for the audience to relate to familiar things.
And more than that there is a significant plot point that I won’t
spoil towards the end of the film that hinges on humans and Na’vi
having similar DNA.....(...)