The body's fluctuations in its 'feel good' chemicals and hormones have been proven to cause bipolar disorder - thus it is a physical illness - just like the body's fluctuations in insulin is deadly to a diabetic, such fluctuations without proper medication and therapy is deadly to a Bipolar Disorder patient. It is 'genetic' in the same way diabetes is. Some families 'tend' to have more of it, and some don't. Personal habits, stresses, situations, and behaviors can make it more likely - but doesn't mean everyone's gonna get it in that family. It is present in both paternal and maternal genetics equally. Various good articles can be found on this topic at: www.webmd.com and at www.associatedcontent.com