I switched from Sociology to Biology because I thought that it would help me out in D-school but looking back I should have finished my sociology degree. I had already finished most of my pre-reqs before the switch and the classes that I have taken to finish my Biology degree (the classes that were supposed to prepare me for D-school) are Ecology, Evolutionary Bio, Genetics, etc.... They are interesting subjects but how much Ecology am I going to need in dental school. My advise (not worth much) is find something you enjoy learning about and major in that. If you love Bio, do Bio, but if you are afraid that you won't do well in undergrad bio classes and that is the reason you choose another major, then you probably will have more problems taking graduate level bio courses.