The origin of language was not due to the basic needs of humans; … It was neither hunger nor thirst but love, hate, pity, and anger that made humans produce our first words. The fruits don’t escape from our hands, one can take them without speaking. One stalks in silence the prey on which one would feast. But for moving a young heart or repelling an unjust aggressor, nature dictates accents, cries, lamentations. There we have the invention of the most ancient words; and that is why the first languages were singable and passionate before they became simple and methodical.Rousseau Jean-Jacques, Essay on the Origin of Language, Chapter 2 (1781).
Mahale chimpanzees, Mahale National Park, Tanzania, September 1999
Up-and-comer Alofu is with Fanana, the reigning boss, at the rear of a small group of chimpanzees walking on the path towards the northern part of the territory, when they sit down to rest during the midday heat. Carter, another young male, takes advantage of the prevailing quietness to move closer to Christina, an attractive adult female with a sexual swelling. He sits facing her with his erection on full display but gets no reaction. Carter then breaks a small leafy branch off of a nearby sapling and, taking a leaf blade between his teeth, rips it apart bit by bit, spitting the cut bits on the ground without eating any of the leaf. He continues to do this with four more leaves, eating nothing but producing this ripping sound, which is just loud enough for Christina to hear. At first she sits up and then she comes to present to Carter. He mates with her quickly as the big males are still sleeping not too far away.
Taï chimpanzees, November 1991
After they finish eating ants, Brutus, Falstaff, and Snoopy climb a big fallen tree that has formed a clearing in the forest and settle down to rest and groom. When young Saphir appears at the edge of the windfall opening with a small sexual swelling, young Snoopy moves towards her with an erection but gets no response. Persevering, Snoopy begins to knock against the trunk of a small sapling with his knuckle. Saphir looks at him then and as he continues his knuckle-knocking, she approaches and presents her sexual swelling to him. Snoopy then mates with her quickly while the big males are still busy grooming.