Bio is more like humanities, it seems, than CS. I've seen Primary Advisers sabotage students in defenses before, it's not fun, and it's not uncommon (~15% of them, maybe). Don't ask me why, but it happens. I even saw a PI sue a student for 'work not completed' after he graduated and the PI signed the forms. The student just went back to China and nothing came of it, but for a few months there it was pretty hairy trying to educate the student in US laws and calm him down.