As an advice all black & white players here already know:
Don't go to level 5 until the patch is released, otherwise you'll be trapped with a tiny creature for all eternity (Or well actually until the patch comes out
).
And The Game I've palyed Black & White for a limited time, I just fed my creature a pig, then rewarded my creature, and then it just associated it with eating, although that was with a tiger not with an ape.