Science

Wild bonnet macaques gesture intentionally

Watch my mouth: Bonnet macaques have a goal in mind and use gestural communication to fulfil that goal.   | Photo Credit: Shreejata Gupta

Gestures are an important aspect of human communication. Until now, gestures in apes were believed to lie at the evolutionary roots of human language. However, a recent study on wild bonnet macaques implies that gestural communication — the basic tools for language — is observed even in that species. Given that monkeys diverged from apes (including humans) much earlier than humans diverged from other apes (such as chimpanzees and gorillas) this finding has an evolutionary significance as well. The study has been published in the journal Behavioural Processes.

Species ethogram

Anindya Sinha from National Institute of Advanced Studies, Bengaluru, who has been studying the behaviour of bonnet macaques in the Bandipur-Mudumalai region for close to 25 years, had developed an ethogram of the species. In essence, a list of objectively-defined behaviours — an ethogram — becomes the reference document for subsequent studies.

Developing on this, the researchers recorded 32 independent gestures made by the bonnet macaques. Of these, they could not identify the context for eight gestures. For the remaining 24 gestures, they were able to identify the context of use. “It would have been perfect if we could get all the behaviours videographed,” says Shreejata Gupta who worked on this problem, in an email to The Hindu. Now a postdoc at York University’s Department of Psychology, she explains how this made it difficult to address some features of intentionality, such as changing body orientation according to the receiver’s orientation.

Differential grooming

“When I first saw the bonnet macaques using their grooming gestures possibly referring to body parts that they intended to be groomed, I was absolutely elated…” she recalls. After accumulating more of these observations, the team published a paper on referential grooming in bonnet macaques, a cognitive capacity that was earlier believed to be restricted to human and non-human apes. This was published in the journal Animal Cognition.

“Bonnet macaques have voluntary control over their gestural communicative signals. They have a goal in mind, and they communicate with others to fulfil that goal. The entire process requires complex cognitive capacity, different from an involuntary action such as an alarm call at the sight of a predator,” says Dr Gupta. It has been known earlier that apes such as humans, chimpanzees, bonobos, gorillas and orangutans communicate intentionally. This study extends this behavior to monkeys.

“This continuity of similar cognitive processes underlying communication systems of monkeys and apes imply that our minds have had the building blocks of producing complex language for millions of years,” says Dr Gupta.

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Printable version | Oct 28, 2020 4:03:53 PM | https://www.thehindu.com/sci-tech/science/wild-bonnet-macaques-gesture-intentionally/article29605142.ece

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