Good Baseline Assumptions
In my work, I have always assumed that intelligence, self-preservation, and a passionate desire to acquire and to defend that which is acquired, form the core of any psychic structure of any alien race that I encounter.
Sexuality is linked to aggression, but the relationship is very complicated. I have assumed a strong sex drive in all species I have written about.
Wildly different conceptions of just about everything else are possible. All one needs to do is to look at the different religions that have sprung up in different cultures, the different metaphysical and cosmological systems that persist to this day to see that having a similar psyche in no way determines how we encounter the world and how we attempt to understand it.
Conclusion
Thus I hope to give my readers the best of both worlds: a familiar seeming presentation of a pluralistic society nevertheless composed of many different species of intelligent life with a variety among and between those cultures that I hope fills them with as much wonder as it does me.
