Servo AF is different from Face and eye tracking in that it is only active as long as a focusing button is active. In the following video, Canon explain that for setting up BBF, one sets up servo focus, and then tap the BBF button to focus (and then stop) on a static subject, but if that button is held down, Servo will follow the selected object as it moves - even if it is not a face or eye. Even if you don't use BBF, it hopefully demonstrates the principle.
That is different from Continuous Focus that would cause the camera to continually focus as long as the camera was turned on - an excellent way of draining the battery. I have noticed that feature disappearing from the menu systems of some models now.
Face and eye detection intelligently look for faces and eyes and will track them as long as the focusing system is active.
For more detailed investigation of this you might find these interesting:
and
They might be helpful in some general info on the subject
cheers, TREVOR
"The Amount of Misery expands to fill the space available"
"All the variety, all the charm, all the beauty of life is made up of light and shadow", Leo Tolstoy;
"Skill in photography is acquired by practice and not by purchase" Percy W. Harris
