Ah, now that's the 64 Billion Dollar Question, in'it?
Most anthropologists dislike the term "human nature" for a lot of different reasons. Mostly because it leads people to think of a set of inflexible laws or unchanging truths. We aren't inflexible or unchanging in anything, however.
Basically, I believe we really are primates. We share a lot of instinctive reactions and drives with our primate cousins, especially the chimpanzees. These built in needs and reactions are immensely strong but very simple: desire for security, need for approval, hunger for status within a group, and so on. They also vary from individual to individual, probably more so among us than among other primates. Our individual emotions, opinions and personalities grow over time as we try to satisfy these instinctive needs.
The upshot is that yes, I think these behaviors are entirely natural but no, I don't think they're inevitable. Humans have the luxury of consciously changing the way we satisfy our own inner monkey.