Good evolutionary hypotheses generate testable predictions about the trait being examined. This can lead to other predicted (testable) effects, and so on, building evidence (or lack thereof) for an idea. Just because we can't draw definitive conclusions doesn't mean there is not strong evidence for many evolutionary theories.

> Evolutionary psychology is ... not popular with cogsci depts...

That's a shame. It seems there is a lot to be gained from a comprehensive approach to understanding.

You may have heard the phrase “nothing in biology makes sense except in the light of evolution" (Dobzhansky). Well, this is true for the human brain and psychology, too. We can't correctly address major behavioral issues without a deeper understanding of the evolved functions of our brain.