Friction is not caused by gravity. Gravity tends to work to work on things to keep them on the surface of the earth, but friction is the force or energy generated the roughness of the surfaces involved. It is the resistance you feel when you drag something across a surface.
Gravity is nothing more then the force that pulls towards the earth and does not create friction. you have friction walking/jumping/running and all other things but that is due to the air and gasses you walk thru daily. Think of it this way, When you are on ice if gravity created friction you could walk normally but sense all it does is hold you down the ice lowers the friction you have to the ground creating you to slip and slide. If you can fight this comment please do, otherwise I hopes this helps.