Emotion and attention in humans and animals
One of the most important evolutionary survival skills is the ability to instantly recognise emotions and intentions of others: those of members of one’s own species and those of different species, such as predators. How have these abilities developed in humans and animals? ‘We cannot repeat evolution, so we have to learn from more indirect clues,’ says cognitive psychologist Mariska Kret. She searches for these clues in conscious and unconscious behaviour, in body language, hormone levels, heart beat and in the brain. She compares humans and different primates with each other. But she also studies the coevolution of humans and dogs.
In 2016 Mariska Kret published two articles on new discoveries concerning the question: What sparks the immediate attention of primates? The first publication focused on bonobos, while the second publication dealt with chimpanzees and received an overwhelming amount of media attention.
Attentional bias in bonobos
Do bonobos have an attentional bias? Kret: ‘We have learned from experiments that humans tend to be biased toward negative expressions, like fear, anger and other expressions of a threatening nature. But conducting the same experiments on bonobos, we found that their attention is mostly grabbed by positive behaviour like grooming and sexual behaviour rather than by signs of distress or aggression. This is contrary to what I expected. But looking at evolution, it makes sense. Bonobos evolved under relatively safe circumstances, around the Congo River. There were almost no predators, there was a sufficient amount of food and not much competition from conspecifics (members of the same species) in the same territory. For bonobos it was more relevant to focus on positive signals and the group. Because of this, bonobos turned out less aggressive than humans. Have humans always been more aggressive? They most probably have; this seems to be a feature of the homo sapiens branch. Interestingly, Neanderthals lack a certain gene, related to aggressiveness, that is possessed by humans.
- Read the article ‘Getting to the Bottom of Face Processing’ published in PLOS ONE.
- See a video clip of the experiment
Chimpanzee recognition of buttocks similar to face-processing in humans
‘Kret takes over the media with buttock recognition in chimpanzees,’ wrote the Leiden University editorial office in November 2016. Kret: ‘Chimpanzees recognise each other not only by their faces, like we humans do, but also by their behinds. I did not discover this myself; Frans de Waal did five years ago. Chimpanzee buttocks are eye-catchers. They are a direct indicator for fitness, and they influence sexual selection. For example, when a female chimpanzee ovulates, her behind becomes enlarged. ‘
Together with Masaki Romonaga from the University of Kyoto, Kret went a step further. She wanted to find out whether the same neuropsychological mechanisms were at work in this chimpanzee buttock recognition process as in human face-processing. Their findings show that this is the case. Kret: ‘Humans recognise faces immediately, just like chimpanzees do. From brain research we have learned that humans have a “shortcut” in their brains for immediate facial recognition. We also know this shortcut only works when we see faces right side up, it doesn’t work when we see faces upside down. We call this the face inversion effect.’
‘We also found the inversion effect with chimpanzees. They were slower to recognise the behinds of their conspecifics when the image was shown upside down. Although we have not done research on the chimpanzee brain, we suspect that they make use of the same shortcut when viewing the behinds of their conspecifics except when the image is shown upside down.’ In the experiment, researchers had chimpanzees choose images on a touchscreen.
Orangutan in the Apelheul primate park
There are not many scientists that study both humans and animals, says Kret. Kret herself studied psychology and got her PhD in neuropsychology. Until then she only studied humans. Kret: ‘At the end of my PhD project I was at a convention and attended a session on the biology of social cognition. That sparked my interest, as I had already been interested in the evolution of cognition. There I met a Japanese biologist and later went to Japan for a postdoc fellowship. During that time I worked as a psychologist among biologists studying chimpanzees. That was a real eye-opener for me. In the Netherlands I went back to studying humans, but I also started collaborating with the Apenheul primate park to study bonobos. It is very interesting to compare humans with animals, preferably on the same tasks, and to study animals using techniques from experimental psychology.’
You can use an MRI scanner or EEG research to study the human brain. As Kret explains: ‘This isn’t allowed when studying apes, so I use non-invasive methods: an eye-tracker that follows their eye movement or a thermic camera that measures the temperature of their faces. When you notice subtle differences between humans and bonobos, it reveals something about their evolutionary course through history. When observing humans and apes you can detect similarities in behaviour, but the underlying mechanisms can be completely different.’
‘We hope our research on emotions can eventually contribute more insight into decision-making processes,’ says Kret. ‘It also makes us think: a different animal can be just as emotionally complex as we are. What kind of ethical implications does this have? What is our responsibility as humans?’
In 2017 Kret will also study orangutans in the Apenheul primate park. ‘Orangutans are of great interest because they are the only anthropoid ape that lives in semi-solitary conditions. And this time the research will not be conducted during the winter, when the primate park is closed, but during opening hours. We want to engage visitors and have them undergo the same experiments as the orangutans.’ Kret not only work swith primates, but also with dogs. ‘Dogs and humans shared a part of their evolution, and humans have had a major effect on the selection process. This makes it interesting. Dogs are quite adept at communicating with humans and recognising their emotions. It would also be interesting to conduct research on domesticated wolfs.’
Mariska Kret: ’I am interested in studying emotion and thinking about it from an evolutionary perspective.’
Photo of bonobos by Joke Kok