Question of the day, nay...of the year

Ladies and gentlemen, I present to you a query that has befuddled some of the greatest minds of our generation. When you shave your head, it continues to grow and will do so until you cut it again. If you shave, say, your legs, the hair will grow back but will cease to do so at a certain, pre-determined length. The same goes for chest hair.

My question for you, faithful readers, is...how do it know?

I want mass response and research. This quagmire of a riddle must be solved and it's apparently up to us. Emails, libraries, expert testimony, wikipedia, the works. Let me know what transpires.

Also, I promise this is the first and only time you'll ever see softcore gay porn on this site. Probably.