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I have a question about Avatar universe. Most animals on Pandora are hexapodal. Why then are Na'vi tetrapodal?
I think that they should be closely biologically related to another animals, since they can establish Tsaheylu with one another which implies similar nervous systems. So their body structure should be similar too. (Although possibility of tsaheylu with Eywa screws this argument)

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    I doubt that much thought was put into this. They wanted the Na'vi to be mostly human. Rather than like the martians in A Princess of Mars – DampeS8N Mar 18 '11 at 13:19
  • We humans have no tails, despite all (most?) other mammals do. – o0'. Aug 26 '14 at 23:07
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If you look at things like the prolemurs, they have two digits on both sets of hands. Also the arms are fused at the elbow. Given the dominance of a hexapodal body plan on Pandora, it is feasible to suppose that the Na'vi share a common ancestor with the rest of the pseudo-mammalian creatures on Pandora, but have gone down a significantly divergent evolutionary route where the arms have fused to form one pair with four-digit hands, with a finger altered into a thumb analog.

From James Cameron's Avatar: A Confidential Report On The Biological And Social History Of Pandora pp. 90–91.

Prolemuris.
… It has two arms that bifurcate into four forearms; the upper bones of the arms have fused, enabling mobility as they navigate through the trees. (Biologists believe this may be an evolutionary precursor to the two-armed Na'vi).

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It is possible that the Na'vi diverged from their hexapodal brethren a long time ago, biologically speaking, and that the evolutionary pressures that lead to them being bipedal (or, initially, standing on their rearmost legs only) encouraged the dwindling of their central limbs.

A second pair of limbs is ungainly when you are standing on your hind feet - the added weight makes balance difficult without providing a significant use. Thus, having reduced midlimbs would benefit a bipedal creature, and they would be selected for.

Of course, they can't have diverged too far back, since the relatively complex nervous system (which provides a HUGE benefit, and would have been selected for) that allows them to establish their brain-USB links was fully developed.

So the birds, horses, various monsters, and Na'vi share a common, 6-legged ancestor that could establish Tsaheylu, which then diverged into multiple subspecies (possibly due to a massive die-off of other species, allowing them to spread into new areas.

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    This is, of course, only one possible in-universe explanation. The real reason is that the Na'vi had to be human-like enough that audiences would empathize with them, and the brain-USB was needed because it's cool and provides a direct, visible, easily-hand-wave-explained 'connection' to the other creatures and the planet itself. Basically driving home the point with the subtlety of a sledgehammer. – Jeff Mar 18 '11 at 13:27
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    The interconnectedness of the planet also strongly suggests a very old technological intervention. Possibly genetic engineering. That, or all of these species, including the plants, probably share common ancestry with whatever life-form first evolved this biological network. – DampeS8N Mar 18 '11 at 13:29
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    The Mountain Banshees only have 3 limbs as well, 2 wings, 2 legs. See this. Perhaps the Na'vi are closely related to them? – user1027 Mar 18 '11 at 13:58
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    Whoops, I mistyped 4 there. They have 4 limbs not 3! – user1027 Mar 18 '11 at 14:17
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    Oddly enough Leonopteryx seems to be hexapod, unlike Banshees. =) – alpha-mouse Mar 18 '11 at 14:36
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Perhaps the Nav'i are from another planet/evolutionary track. And the reason they developed the neural connection is the evolutionary influence of Eywa.

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There is a potential answer to this which suggests a far more interesting story beneath the one that actually made it in to the final cut. (admittedly this isn't supported by any official commentary, but does make sense within the context of the movie its self.)

Remember that mid-way through the movie the scientist talks about the trees forming a network several orders of magnitude greater than a human brain.

Also that the USB-hair works only one way, with the Na'vi controlling their mounts and other animals and communing with the tree of souls but not the other way around.

Also remember that James Cameron knows his science and does not break the speed of light. The Wiki says that the voyage by the vessel at the start of the film takes 6.75 years.

It's reasonable to assume that prior voyages took longer as engine technology improved, meaning that it could be a few decades between first contact and the events of the film.

If Pandora is a living, intelligent biosphere then everything makes more sense.

The first exploratory expedition had at least one casualty before the survey team returned to Earth to report the rich finds on Pandora, at this point they did not encounter the Na'vi (they reason that it's a big planet) but at this point, that species does not exist.

The Na'vi are an artificially designed species made by the Pandora intelligence as a means of interacting with and understanding humans (Meaning that Avatar refers both to the Na'vi themselves and the artificial copies made by the humans). This is why it is relatively easy for humans to reverse engineer their own Avatars, it is also why they are radically different to all other life on the planet, because they are designed to look broadly like humans despite having the same biochemistry as the rest of Pandora.

Given that the scientist and the main character are uploaded to the planetary consciousness in the movie it also suggests some very dark implications about the end of the movie.

It's a pity that they decided to go with Dances with Wolves, when there is in fact a much smarter movie underneath all of that. An encounter with a form of life so alien to humans that it isn't even directly noticed by the humans is very much in James Cameron's style.

  • Very interesting, but is this pure speculation on your part? Personal theories are really not appropriate for this site. – Ernest Friedman-Hill Jan 7 at 3:41
  • You've got to admit that the speculation is eerily consistent though. – alpha-mouse Jan 9 at 12:34

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