Human speech could have evolved from monkey lip-smacking, an affectionate gesture that monkeys make towards each other.
Asif Ghazanfar at Princeton University in New Jersey, Tecumseh Fitch at the University of Vienna and their colleagues made X-ray movies of macaques during episodes of lip-smacking. The monkeys moved their lips five times per second — the same frequency as occurs in human speech, and much faster than when the monkeys chewed. Moreover, the monkeys' lip movements were independent of their throat movements during lip-smacking, much like human speech.
Curr. Biol. http://dx.doi.org/10.1016/j.cub.2012.04.055 (2012)