It will help, especially if you do something a little more interesting than politcal science. With poly sci they will assume you planned to go to law school and changed your mind. Something like majoring in a language, anthropology. Unless Poly Sci really interests you. It is also a fairly easy major at most places which will help your GPA.
They get tons of applications from Biology majors. You will still need to do the basic pre med requirements and do well in them