Sounds like you're working on another story, R.L.

It's not easy - in fact, it may be the hardest thing in SF to do: making aliens who are convincingly alien, but still sympathetic enough to human readers. Common moral ground is probably more important than common ground in other areas... after all, math and physics are isotropic.

The most successful aliens, IMO, fall into two categories. On one hand, there's the Star Trek type, who are figuratively, as well as literally, humans in exotic makeup. (David Brin's second Uplift trilogy is an even better example). Their characters serve as ways to highlight human traits by taking them into a different context. On the other hand - or maybe I should skip right to "gripping hand" - there are the aliens of Larry Niven, most notably the Moties, but the Puppeteers also serve (Vernor Vinge has concocted some good ones, too). They are as truly alien as it is possible for a human author to create while keeping them understandable.

I don't know that's it's possible to predict shared morality. Your implication about evolution is accurate... which brings us to shared biological imperatives. Self-preservation is #1, followed closely by species preservation, which is usually manifested by the urge to propagate; less often by altruistic acts of self-sacrifice to save a greater number. Number 3 on the Hit Parade, in humans, may well be curiosity, which in some of us is strong enough to overcome #'s 1 and 2.

If I'm right, and you're thinking of a story, you really could go either way with this, depending on how you want to use it to further the plot. Perhaps they're so alien that there's no common ground at all - and that's the problem to solve. Perhaps there's semething shared, and the story may partially involve understanding why.

I'm looking forward to reading it.