Even as an adult, when I'm really focused on something my right leg gets a mind of its own and just starts bouncing up and down rapidly. Maybe there's an evolut

Even as an adult, when I'm really focused on something my right leg gets a mind of its own and just starts bouncing up and down rapidly. Maybe there's an evolutionary purpose to it (increasing blood circulation perhaps), but I've always found that when I force myself to be perfectly still I just don't focus as well.