17February2019

Did the human speech evolve from monkeys pulling faces?

X-ray survey finds that primates use complex ‘language’ of lip smacking expressions

Gist:

  • Lip smacking gestures work at same speed as human speech
  • Vowels and consonants work in same way as smacking lips
  • The noises made by monkeys are largely innate – and unlearned – and lip-smacking is learned and much more complex

Human speech might not have evolved from the ‘hooting’ noises made by our closest animal relatives, chimpanzees. Instead, our complex languages might have come from the lip-smacking gestures made by primates.

The facial gestures made by chimpanzees and other primates are highly complex – and a new X-ray study suggests that face-pulling might have been at the root of speech. A study found that the gestures occur at the same speed as speech – and that our vowels and consonants correspond to the way monkey families smack their lips.

Researchers at Princeton and the University of Vienna used x-ray movies to investigate lip-smacking gestures in macaque monkeys. Chimps and orangutans also make similar gestures.

Lip smacks are made by many monkey species in friendly, face-to-face situations (e.g. between mothers and their infants). These movements occur at a rate of about five times per second, the same as speech. Although lip-smacking makes a quiet sound, it is not accompanied by phonation, which is produced by vocal cord vibration in the voice box. or larynx.

Although superficially lip-smacking appears to involve simply rapid opening and closing of the lips, the x-ray movies show that lip-smacking is actually a complex behaviour, requiring rapid, coordinated movements of the lips, jaw, tongue and the hyoid bone.

These observations support a long-standing hypothesis of Peter MacNeilage and his colleagues that the roots of human speech do not lie in primate vocalizations, but are closer to these fascinating facial signals used for communication by monkeys.

In particular, the alternation between vowel and consonant that generates speech syllables is strikingly similar to the movements underlying lip-smacking.

Chimpanzees also make communicative sounds with their lips, including both loud lip smacks and lip buzzes  These lip gestures appear to be under voluntary control, and can be learned (unlike hoots or grunts). Similarly, orangutans can learn to whistle: again a sound produced using the lips and tongue, rather than the larynx.

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