One thing that I have found most annoying about the movie Avatar is the chorus of praise for its "scientific accuracy." I don't know of any movie short of Star Trek that has tried so hard to convince its fans that it's based on real science, and fallen so short. So I thought it would be useful to just make an archive showing that the movie is not science-fiction; it's science mixed with fantasy.I know I promised this week to cover the moon of Pandora, but it's taking longer than I thought since astronomy isn't my specialty, and I want to get it right. So instead, we'll be looking at another famous aspect of Avatar, creatures with six legs.Most of the dominant lifeforms on Pandora have six limbs, making them what's known as
hexapoda (Greek for "six legs"). Some hexapods in the movie are a horse-like creature called the
Direhorse, a panther-like creature called a
Viperwolf, and a pterodactyl-like creature called a
Mountain Banshee. All of them have six limbs.
On Earth, most creatures are
tetrapods, meaning they have four limbs. That includes everything from dogs to horses to humans. The only creatures that have six limbs are
certain insects. There's a reason for that; four is a good number of limbs. Not too many, not too few. While one could argue that having four arms would be useful, it's not really necessary. Even if you needed or could use another set of hands, primates solved this problem by having
opposable toes on their feet, turning them into a second pair of hands. Adding more limbs would just require more brain-power to control them, and would require a major change in configuration that would mean that it would have to have some benefit.
While no one really knows exactly why insects have six limbs, we do know that it's an advantage to them as opposed to animals. When a creature runs on two or four legs,
only one or two feet remain in contact with the ground at all times. When a six-limbed insect runs on a surface,
three limbs usually remain in contact with the ground at all times. For a wall-crawling insect like a fly or a spider, this is an advantage because it means greater stability when clinging to a vertical surface or upside-down. That's not an advantage that animals need walking upright on a flat surface.
In many ways, six legs would hinder normal creatures. For example, insects on Earth that have six legs have them splayed out from the body so they don't get in each other's way. In
Avatar, all the creatures have their six legs in line with their bodies, which would cause them to bump into or get tangled up together easily. It seems like the designers knew this, so they tried to adjust for it.
Let's look at the Direhorse, for example. It was a speedy creature in the movie, but take note that they animated the Direhorse to run just like our four-limbed horses with the front two legs moving together and the rear two legs moving in the opposite direction. This would be a recipe for disaster, since the forelegs would only work if they were exactly in sync. The slightest misstep on any of the four forelegs would cause the creature to trip on its own limbs and fall. The Direhorses should run more like cockroaches, alternating three legs at a time. That would actually cause them to run slower than Earth horses, which goes back to our original point…they would be better off with four legs.
Then there's the obvious fact that the Na'vi have only four limbs; two arms, two legs. But that's for another post.
Further Reading:Avatar's Walking With HexapodsNEXT WEEK: Pandora (seriously)
What do you think about Avatar's six legged beasts?
Maurice Mitchell
, 1971), and 
(1956; filmed as The Incredible Shrinking Man, 1957) for which he earned a Hugo award. Matheson's publications and film work often explore themes of human existence facing alternate reality and incorporate the paranormal, terror, survival and ardor.
. It's mind-blowing in its scientific explanation of vampirism and sense of isolation.
DVD last week I was left wondering about the sequel. Cameron's hinted at a lot, including delving into the oceans of the scientifically implausible Pandora. I hope they don't run into Jar Jar Binks. [
