Biologists have long failed to find the primitive expression of speech in primates, but all previous studies have focused on the sound research they produce. The study authors argue that human speech arises not only in the evolution of sound, but also on the movement of the lips.

It is known that people around the world, regardless of their language, in conversation often open their mouth 2-7 times / second, each cycle corresponds to one syllable.

Comparing videos of four pan troglodytes populations: two wild chimpanzees in Uganda and two kept in zoos in England and Germany, researchers found that the primate’s lips move with an average of 4 "syllables" / second.

However, there was no significant difference in the average lip movement speed between captive and wild macaque populations.

The authors suggest that the chimpanzee chuckling plays the role of speech, in that way they attract attention, convey emotions and information. Combined with the special sounds the animals make when they take care of each other, these rhythmic movements are an important element in social interaction and interaction between individuals.

"Our findings support the hypothesis that primate lip rhythms are used to attract attention - researcher Adriano Lameira from the School of Psychology and Neurology at St. Andrew University in the UK. said.