What I don't get, if the Shivans were just afraid of aliens:
1. why do they keep attacking everyone else?
2. why are they still afraid after being the only known species with the ability to blow up planets, stars, etc.? They're obviously the big kids on the block.
I think the idea advanced by the Ancients monologue is supposed to be the canon one, although humans could also just be in season every 32 years...