Presumably you mean mental urges, not physical. Without those "urges", the species will die, so they exist. Or we would not exist as a species.
Nerves have to do with it because your brain (mind) is composed of nerves. It is what controls every action of your body, from your heartbeat to moving your arm to the urge to feed a baby. And the placement, interconnection, number, etc. of those nerves in your skull are controlled by your DNA (and to a lesser extent the environment).