That includes first of all the "source" - the vocal folds that humans and many animals share.

BBC: Helium-huffing gibbons 'sing with soprano technique'

"When humans laugh, they voice stable sounds: that means the vocal folds are moving in a very regular synchronised way, " Dr Davila-Ross explained.

BBC: Tickled apes yield laughter clue

Singing too has evolved, and soprano singers reach their piercing high notes by precisely controlling the shape of their vocal tract to match its natural, resonant frequency with multiples of the one being produced by their vocal folds.

BBC: Helium-huffing gibbons 'sing with soprano technique'

In the procedure, called injection augmentation of the vocal folds, a doctor threads an endoscope through the patient's nose or mouth into the throat, then injects a tiny amount of collagen, fat, hyaluronic acid or a gel filler into the vocal cords to plump them up.

WSJ: How to Take Years Off Your Voice

In a general sense, vocal cord paralysis can be more difficult to treat since the main focus is to make the folds further apart to improve the airway, but not so much as to affect the quality of the voice.

FORBES: Move up http://i.forbesimg.com t Move down