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Orangutan kisses point to dawn of spoken language

(9 February 2017)

New research may help to unlock the mystery of why and how our evolutionary ancestors first combined a consonant with a vowel to make the first word.

Kiss squeaks

The research, led by Dr Adriano Lameira of the Department of Anthropology, is published in the journal Nature Human Behaviour.

The study has analysed over 4,400 individual recordings of voiceless consonant-like calls, or ‘kiss squeaks’, from 48 orangutans in four different populations.

Orangutans are unique among non-human primates as their predominant call type, the ‘kiss squeak’, is voiceless.

The aim of the research was to understand whether these voiceless calls, which can also include lip-smacks, clicks and raspberries, could transmit similar information to voiced calls, which more closely resemble vowel-like sounds.

The team believes that understanding what information these consonant-like ‘kiss squeaks’ contain would help to piece together how and why the earliest combinations of vowel-like and consonant-like sounds may have occurred.

Non-vocal information

Researchers already know that population membership, body size, individual identity and situational circumstances can be conveyed in the sound frequency and duration of voiced, vowel-like calls in other primates. 

In this latest research Dr Lameira and his colleagues found that the sound frequency and duration of orangutans’ ‘kiss squeaks’ also varied depending on similar criteria.

Dr Lameira explains: “We found that orangutan body-size significantly affected the maximum frequency of the kiss squeak, whilst the context in which the squeak was made affected duration of the call. Our study also indicates that population membership and individual identity affects the frequency and duration of the kiss squeak.

“These findings suggest that consonant-like calls are potentially as adaptive as vowel-like calls, so the communicative functions of both call types may have been equal.”

Message repetition

It is more likely, the team argue, that these early sounds, known as ‘proto-consonants’ and ‘proto-vowels’ were first combined to transmit the same information via different acoustic channels. This combination of proto-vowel and proto-consonant sounds could have given rise to the earliest syllable or word.

Dr Lameira explains: “Our research indicates that both types of sounds convey similar information, so combining them would have strengthened the message a sound conveyed, rather than adding new information.

“Understanding the meaning behind early consonant and vowel sounds helps us to get closer to understanding the point in language evolution when consonants and vowels became inseparable. Ultimately we hope to be able to reconstruct speech evolution, to understand the basic building blocks, how they came together and in what order.” 

The research also included experts from Liverpool John Moores University, University of Amsterdam and Boston University, USA.

Listen to an example of the Orangutan kiss squeak.

Image credit: Tim Laman - ‘Kiss squeak by flanged male at Gunung Palung’

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