pfff that was shorter and more correct than mine. could you elaborate for sake my curiosity?
(Edit: op, somehow I missed this was asked a long time ago. Oh well!) My understanding is that the energy interacts to determine this. There is a conversation and a communion that happens when universal/jing energy meets man or woman and is properly applied to individual cases and needs.
Similar to when looking under a microscope, cells interact with other cells and know how to locate and kill cancer cells, for example. There is an inner mechanism for attraction that creates the pathway for its purpose.
Perhaps you’re looking for the name of that mechanism. I don’t have a name for it, but when I “view” the inner workings of what’s happening, there is an energetic “cellular” conversation occurring and the proper energies are provided and integrated.