For me, interpretation of theme was where this game scored the highest. Evolution is a long story of figuring out how to deal with energy, and I think you can make something out of that.
Consider giving the player a few different directions to evolve in, to suit how they want to play. Perhaps make pacifism as much a valid strategy as fighting is, and introduce the same trade-offs you find in nature. If you want more armor or physical strength you're going to have to give up other key traits, as thermodynamics won't let you have them all! For a pacifist/social strategy you could even introduce mechanics that allow you to interact with the other squids, that they protect you or share their energy with you.