Once a year, I go back to my alma mater and do a guest lecture about biological clocks in an Anatomy & Physiology class. Knowing how many pre-meds are among the 200 students in the room, I try to start with some examples of rhythms in human physiology (and disease), and the first one is body temperature, busting the myth that 98.6F (37C) is the “normal” temperature:

Now Orac links to an excellent post that explains it all – the entire history of the idea that 37C is normal and what the real difference, means and fluctuations there are. Read the whole thing.
