James Cameron's Avatar , which premieres on Friday, is already legendary for its meticulous attention to detail. Witness, for example, the hubbub over the invented alien language , which Cameron boasts will "out-Klingon Klingon." Or the fact that he gave every plant and animal on the planet Na'vi, Latin, and common names , all catalogued in a 350-page "Pandorapedia."
Cameron seems to have been a little more lax in the biology department—at least when it comes to imagining Pandora's reigning creature, the Na'vi. Take those already infamous alien boobs : He gleefully told Playboy , "Right from the beginning I said, 'She's got to have tits,' even though that makes no sense because her race, the Na'vi, aren't placental mammals."
One hundred percent plausibility isn't required from any fantasy creature, of course. And if audiences grok those tall blue cat-people, then biological quibbles will be moot. But Cameron's admission got the science nerd in me curious about the finer points of Na'vi anatomy—so I called up Stuart Sumida, a biologist at Cal State San Bernadino who moonlights as an anatomy consultant for FX studios. (He helped work out how the mythical creatures of The Chronicles of Narnia should look and move.) I asked him to watch the Avatar trailer and pre-release clips and to offer an initial assessment of the Na'vi.
Sumida notes that the trickiest part of making a creature using motion-capture technology is that its movements remain essentially human. ("It's still basically a guy in a suit.") But with their long limbs, heavy tail, and opposable big toes, the Na'vi should move more like gibbons than bipedal humans. And all that upright scampering across tree branches seems wrong, too, given how heavy a 10-foot-tall creature must be—even one with superlight bones.
Many of the choices that have obvious rationales from a storytelling perspective make for weird anatomy. Take those big, exotic eyes, which make the Na'vi look so cute and sympathetic. "Gigantic eyeballs are usually for creatures that forage exclusively at night," Sumida says. "These characters should be wearing sunglasses—they get so much light, their eyes will hurt."
And those expressive tails . Tails are an extension of the backbone, emerging downwards from the sacrum , where the hips attach. Na'vi tails, however, seem to emerge from above the sacrum, and they stick out at a nearly right angle. Sumida also takes exception to the Pandorapedia's claims that those tails are prehensile—that is, used for grasping things—and help the Na'vi balance their long torso and legs. If that were the case, the Na'vi would probably be walking on all fours, with their backs parallel to the ground.
Finally, about those boobs: It's good that they're purely decorative. Since the Na'vi seem to have zero fat on their bodies, those mammary glands almost certainly don't work. Relatedly, the fact that the Na'vi aren't placental mammals makes the presence of bellybuttons something of a curiosity.
However, the glittery blue skin that's earned the Na'vi unflattering comparisons to the Smurfs —and which seems to be the outgrowth of a rather awkward racial metaphor —doesn't bother Sumida. "Bioluminescence seems like a valid evolutionary strategy," he says. "I think it's one of the coolest things they've come up with."
Finally, an Easter egg for eagle-eyed viewers: If you look closely, you'll see that the Na'vi have a little muscle running down their necks . We've got them, too—it's called the sternocleidomastoid muscle —and it's a uniquely mammalian feature. Ours make a very distinctive V-shape, and when creature designers want an alien to seem attractive and familiar to its human viewers, they often slap one on. "Even C3PO has it, in the form of little pistons on his neck. Watch Star Trek : The good guys always have them, and the bad guys don't. It's a classic alien designer trick."