RHYTHMIC MONKEY VOCALISATIONS HINT AT EVOLUTION OF HUMAN SPEECH
The sounds made by marmoset monkeys are built from individual syllables of fixed length, much like human speech, researchers at the University of Tübingen, Germany have found. Such a rhythm may have been a key step in the evolution of true speech, they say.
Whether saying a short word such as ‘hi’ or a longer one such as ‘floccinaucinihilipilification,’ everything humans say is made up of smaller units of sound lasting an average of one-seventh of a second, regardless of the language spoken. This rhythm is inherent in our production of syllables, and is due to the structure of our voice boxes and the neural processes that control speech. The Tübingen team has now found that the vocalisations of marmosets, a type of small primate found in South America, also share this feature. They recorded thousands of the monkeys’ cries in a sound chamber, interrupting them at random intervals with bursts of white noise which caused them to fall quiet.
“The marmosets’ ‘phee’ cry had so far been considered part of their basic vocabulary, alongside the ‘tsik’ and ‘ekk’,” said Thomas Pomberger, co-author of the paper in the journal Current Biology detailing the research. “[But] we observed that they would stop right in the middle of their ‘phee’ calls when disrupted with noise. Moreover, that would only happen at specific points within the call.”
This means that the long ‘phee’ call is made up of small units about the same length as the ‘tsik’ or ‘ekk’ call – around 100ms. It’s essentially the monkey equivalent of a multisyllable call.
“Until now, the supposed existence of the long ‘phee’ has not allowed for the conclusion that we can draw now,” said Dr Steffen Hage, who led the research. “Like us, marmoset monkeys have a ‘hardwired’ rhythm that controls their vocalisation. It is even similarly fast.”