GAs are used where there aren't hard-defined answers like you want. Where you can't exactly quantize every single potential input and output. Where the answer is more like the judge's conclusion on pornography: "I'll know it when I see it".
I'd suggest this as an excellent primer on GAs, and also the Wikipedia page on GAs as good background.
Like so much with life - where the answers/solutions are varied and shaded and fuzzy - GAs excel at operating in those situations.
And that is the intelligent part.(along with the darn program to implement the process)