What's STEM like at UoP?

Starting classes at UoP as a STEM major is relatively normal.  You attend your first major-specific class with 20 to 25 other people.  As the semester goes on you start to talk to those around you and make some new friends.  The topic of majors comes up and everyone says their major.  “Pre-dent.”  “Pre-pharm.”  “Bio-chem.” “Computer Science.”  You and maybe one other person is a natural science major.  No worries through, right?  There’s nothing wrong with being a little uncommon.  Time flies by and the semesters come with it.  Every semester, your classes are populated with less and less students and by the time you’re a fourth year, there are 5 to 8 others in your major-specific class/classes.  At least you and that one other natural science major are good friends by now, considering you've seen them in almost all of your classes.  Silver lining aside, what happened and where did everyone go?