Chimpanzees can “catch” yawns from an android robot imitating human facial expressions, according to a new study that raises more questions about the evolutionary origins of the behaviour.
Yawning is known to be associated with attention changes, regulating body temperature, and as a transition between rest and arousal.
Contagious yawning is a strange behaviour in which an animal yawns after seeing another individual exhibit the same behaviour.
This contagious aspect of the behaviour has been linked to some elements of social interaction, like empathy and imitation.
Until now, contagious yawning has been observed in mammals and some fish, but its evolutionary origins are still unknown.
It emerges gradually in humans, chimpanzees, and dogs, becoming prominent at around four years in humans, five years in chimpanzees, and at about seven months in dogs, scientists say.
The new study, published on Thursday in the journal Nature, found that chimpanzees will both yawn and lie down in response to yawns made by an android robot.
The findings suggest that observing another individual yawn may act as a cue in chimps to rest rather than triggering an automatic response.
In the study, scientists used an android head that could simulate facial expressions to test the responses of 14 adult chimps aged between 10 and 33 years.
The android head contained 33 rotational motors which functioned as muscles to generate its facial expressions, including yawns, with each expression lasting 10 seconds.
Chimps in the study were each exposed to four 15-minute sessions of the android demonstrating yawning, gaping, and neutral facial expressions.
Scientists recorded these sessions on camera, and each chimpanzee was scored for their responsiveness, along with the amount of time they spent lying down.
Eight of the 14 chimpanzees were found to yawn in response to the android’s “yawn” expression.
“The results showed that adult chimpanzees exhibited across-agent yawn contagion, with a graded response: the highest contagion occurred when the android displayed a fully wide-open mouth, a reduced response when the mouth was partially opened, and no contagion when the android’s mouth was closed,” they wrote.
Eight chimps also lay down in response, and some gathered bedding before lying down.
“Chimpanzees engaged in behaviours associated with drowsiness, such as gathering bedding materials, constructing nests, and lying down, while observing the android yawning,” scientists wrote.
These findings seem to show contagious yawning due to an inanimate model for the first time, according to researchers.
The results shed further light on primates’ susceptibility to contagiously induced behaviours, scientists say, adding, however, that the exact biological mechanisms surrounding it remain unclear.
They hope future research can reveal whether other actions performed by robots are contagious to animals.
