Applying to Ph.D. programs in history when my degree is in a science field
This depends on your institution, but most likely, yes you will need to have a certain undergraduate background. History is a field that requires a background, and this will be needed for PhD studies. Nevertheless, as you do have a science degree, I believe that there are programs that will accept you into terminal M.S. programs where you can then apply for a PhD. My advice - look around, email faculty, and apply.