A team from St Andrews University translated the meaning of gestures that wild chimpanzees use to communicate, revealing that man's close cousins use 19 specific messages to one another with a "lexicon" of 66 gestures.
The study reveals for the first time what wild chimpanzees are trying to say when they communicate with their body and hand movements.
For example, a chimp very obviously taking small bites from leaves is signalling "I'm up for it" to sexual partners. And a mother chimp waving her foot is saying to her children, "jump up, I'll carry you".
The scientists filmed communities of chimps in the rainforests of Uganda.
The work was carried out by St Andrews ape experts Dr Catherine Hobaiter and Professor Richard Byrne.
Primatologist Dr Hobaiter said chimpanzee sign language was the only form of intentional communication recorded in the animal kingdom.
The research is published in the journal Current Biology.