That's plenty of time for selection pressures to modify a culture. Culture—shared knowledge—is communicated much more quickly than genetic changes.

Yeah that's very true. Perhaps I don't mean "evolution" in a classical sense but rather: animals probe the world, and behaviours that aren't discouraged somehow are more likely to be replicated among the community.

Instead of evolution, some sort of epigenics or something?

How about memetics? I see no reason why memes are only for humans. The orcas must be communicating an idea even if they aren't using words.