Female-led bonobos focus mostly on positive, bond-building emotions, unlike male-dominated primates such as humans and chimpanzees, according to a new study.
Research published in the Proceedings of the National Academy of Sciences suggests that while bonobos are incredibly attuned to "emotional" images of their own species, they focus first on positive images.
Humans and chimps, on the other hand, are more alert to signs of danger or aggression.
Bonobos, along with chimpanzees, are among our closest living relatives. They’re known for their intense social lives and friendly demeanour, and their penchant for non-reproductive sex.
For social animals, such as bonobos and humans, the ability to respond to others’ emotions is crucial to survival. Being aware of the emotions of other group members helps us navigate conflict, manage important long-term bonds and even stay aware of social debts. (A chimpanzee, for instance, will remember who has groomed them for long periods of time and "repay" them down the track.)
Bonobos are known for being less aggressive and competitive than chimps or humans. Unlike humans, bonobo society is controlled by females. Conflicts are resolved through recreational sex and grooming, rather than through fighting or killing, both of which are common in the human and chimpanzee worlds.
“Like humans, chimpanzees make war with rivaling groups and do not take kindly to strangers,” the paper states.
“In stark contrast, bonobos live in friendly and tolerant societies and, although they sometimes hunt smaller animals for consumption, never kill one of their own.”
Lead researcher Mariska Kret, a psychologist at Leiden University in the Netherlands, set out to test whether bonobos, like humans, are alert to the emotions of their own species, and which types of emotions draw the fastest response.
She and her colleagues used the "dot-probe task", a test commonly used on humans and primates to establish where their attention goes and how quickly.
A chimpanzee will remember who has groomed them for long periods of time and 'repay' them down the track.
Participants are shown two images side-by-side, sometimes depicting their own species with varied facial expressions or engaging in different activities.
When the images disappear, the test subject must press a black dot on either the left or the right of the screen in order to receive their reward. The response to one image versus another, and the speed of response, is used to measure the participant’s level of attention.
The findings show that bonobos were more attentive to more "emotional" images – that is, pictures of their species experiencing something significant – rather than neutral ones.
Interestingly, their speed of attentiveness increased if the image showed a relatively positive experience, such as grooming or sexual intercourse between bonobos.
When humans have done the dot-probe task, our interest has been piqued by images showing distress or aggression. The researchers suggest this may be linked to our prioritisation of these behaviours, while the bonobos prioritise behaviours that encourage closeness.
“Given their highly social nature, we predicted that bonobos would show heightened attention toward the pictures showing emotional compared with neutral bonobos,” the paper says.
“As bonobos are known to be less aggressive than chimpanzees and humans, and spend a lot of time on positive social behaviours – such as play, sex and grooming – we predicted seeing this reflected in a specific attentional bias toward these more affiliative or protective behaviours than to signals of distress.”
Interestingly, images of yawning bonobos earned the fastest reaction times among test subjects – even more than mating or grooming.
The researchers point out that yawning, which is found among many social species including bonobos, is believed to increase vigilance among a group. Contagious yawning is also a sign of empathy.
Amy Middleton is a Melbourne-based journalist.
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