Re: Na'vi anatomy
I've wondered over this question, and I was told that they evolved from these four-armed creatures that jumped from tree to tree that Perseus nearly shot in the forest. I would take it their four arms merged into two over time. Perhaps that gives them additional strength too.
My pet explanation is that they did not evolve together with the rest of the creatures, and/or that ponytails aren't evolutionary traits, but a product of genetic engineering. I don't see natural USBs and Internet evolving through natural selection as that plausible (certainly less than four arms merging into two). Though I must admit, I had heard that idea before, and I was extremely fascinated by it, so seeing James Cameron put it in his film was a pleasure, plausible or not. I was actually contemplating how it might happen at some point, almost convincing myself that it could.
R.I.P. Admiral James T. Kirk (2233-2267, 1969, 2267, 1930, 2267-2268, 1968, 2268-2269, Serpeidon Middle Ages, 2269, 2237, 2269-2286, 1986, 2286-2293, 2371)