Do we need an ego to survive?
I would argue that having an ego is the least likely trait that would make one formidable against impediments. This is because ego (when unfettered) can cause the most idiotic of actions to transcur. What one would certainly need, is a head, where one can make rational decisions based both on objection, and subjection. You never see lemmings making decisions, the mentally weak are the ones that are the least likely to survive, as they are reliant primarily on others.