I do feel like anger and the vengeance it drives (in particular irrational vengeance that goes beyond restitution) has some evolutionary advantages. In many ways it is like the doomsday device in dr strangelove... the fact that it is not rational, and will be carried out even if it is not in the continuing best interest of the person enacting revenge, acts as a stronger deterrent than a proportional response. It chan…
In this case, anger is a loss response. Sadness is also a loss response but it looks back in time and works to reduce one's activity level, while anger is forward looking and tends to drive one towards more action. (Unrelated, but fear is also a loss response, but a response to a potential loss).
Anger also generally (but not always) requires that the one experiencing anger recognizes the perceived cause of anger as an agent with free will. We don't feel angry, for example, when we get caught in the rain (unless it is at ourselves for not bringing an umbrella). However, we have seen animals (such as chimpanzees and dogs) on occasion expressing what look like anger at inanimate objects that have hurt them.
Perhaps there are other intelligent species out there with a different evolutionary path that has a larger number of primary emotions. And perhaps there are others who only possess one emotion in place of both anger and sadness. It is a subject worth examining from an evolutionary and neurological angle, rather than philosophical.