A few billion beings prior to Sir Isaac may disagree with you there! And again, as a small baby anything you grab (or see someone else pick up/drop/fall) will result in the realisation that things fall downwards. I would say you have learnt that through observation, not through and form of instictive knowledge. However, if you startle a baby (not something you should really do I know) and it does that whole 'shitting itself' face and tries to get away, I would say is an instinctive struggle for survival. It's just a shame that human babies are a bit shit!
I'm not convinced. I'd say food, sex and survival/preservation of yourself and your young are some of the few true instincts which exist.