What do you think is the basis of all human motivation?

In other words, why do you think people do what they do and why do you think they do it that way? I understand this is an incredibly broad question, so I’ll do my best to focus it to a reasonable size.

Today my younger sister and I were in the kitchen. I was making lunch for myself, and she was doing nothing more than watching me. She said something in an attempt to hurt me, which was neither bright nor important to the story. What is important, however, is not half a second after that she made a joke with the intent of making me laugh- in other words, an affirmation that she is capable of being thought funny by someone she supposedly respects. I say respects because I know she didn’t mean whatever it was that she said to put me down (I honestly can’t remember what it was), it was merely a defense against my indifference towards her.

Now, the reason I’m asking this question. My sister’s fickle actions led me to a thought- All humans are slaves to each other. While formulating ways to degrade others in order to protect your own dignity, you look for ways to make them like you more. This is not a standpoint, it is just a thought that that specific encounter led me to conceive. I ran with it and thought that possibly the motivation for everything that everyone does is elevation in social status, or how much people like and respect you. From an evolutionary standpoint, this makes much sense- most social mammals consider elevating themselves in their tiny society second only to finding food (think of a pride of lions).

I wanted to find out what you guys think. Do you believe that everything that most (gotta qualify it) people do is in order to affirm that they are liked by other people? Even as I write this incredibly overlong description a part of my mind is eager to post it so that I might see if any of you respectable people consider me intelligent. What do you think? Please understand I’m not taking a stance, too many of these discussions degrade into arguments.

Also, I understand many prominent philosophers have broached the topic- I want to see what YOU guys think.