Na'vi sociology

[Clarke]

I was more thinking that before you have a "society" at all, you start off with individuals who are greedy to some extent. If they weren't, they wouldn't have survived.

Also, I'm not sure altruism applies to the whole species immediately. You only want people which are similar to you to survive, and that's more likely to be localized to your region/clan/family than it is to encompass the entire species. In fact, if the Na'vi have an equivalent to Dunbar's number, it's exceedingly unlikely to cover the entire species. (Since there are tens of thousands of them in the nearby region alone.)