I frequently look at job openings in various Science/Engineering fields. I've began to notice that for Bachelor's education-level jobs they are very specific as to what degree you need to be eligible. Then at the PhD level the jobs all of a sudden say various degrees are eligible. Something like "Physics, Chemistry, Materials." I'm not talking about skills here, only the degrees. How does that work if as you get higher in education you get more focused in a field. So, why do they begin to be less specific for degrees at a PhD level? Thanks.