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English review - The Mystery of the Clever Ape

In the distant past, the lineage of humans and chimpanzees split from a single ancestor. One of them makes sticks in order to fish for termites. The other makes music, rockets and computers. What is it that sets human beings so far apart from their closest relatives? Radboud Reflects and the Donders Institute hosted an online event on this topic. Neuroscientist Rogier Mars, associated with the Donders Institute of Radboud University and University of Oxford, discussed the evolutionary history and purpose of the brain. Philosopher Marc Slors, professor of Philosophy of Mind and Language at Radboud University, argued that the real distinction between humans and other primates is our ability to generate a ‘collective brain’ by learning from each other. Philosopher Cees Leijenhorst moderated the discussion.

A Family Tree of Brains

Mars started with the enigmatic question: “Why do we have brains?” We are proud of our large brains, but from an evolutionary perspective they seem counterintuitive. For example, human newborns are vulnerable for a long time. By examining the brains of many species that currently exist, Mars charted an evolutionary history of the brain, going back 550 million years.

By walking us through this ‘family tree’, Mars showed that brains become bigger and more complex when an animal has to solve bigger problems to survive. Ascidiacea have very simple brains in their first stage of life, in order to find a nutrient-rich area, after which they advance to a brainless and immobile stage. Reptiles, one of the two large land-dwelling groups, observe their environment primarily by scent. A comparatively large part of their brain is dedicated to this. Warm-blooded mammals require a lot of energy-rich nutrition. This demands hunting behavior that is more selective and complex than that of the reptile. The neocortex gives all mammals this cognitive flexibility.

A Demanding Environment

This pattern applies to our close relatives, primates and great apes, as well. Primates are specifically adapted to living in trees. An image of an early primate shows typical adaptations: the eyes have moved to the front to allow for depth vision and the hands are suited for grasping and climbing. Primate brains have large areas dedicated to visual processing and motor functions. Great apes inhabit tropical rainforests and subsist on fruits. They must navigate the dense foliage, avoid poisonous fruits and decide whether a journey to a fruit-bearing tree is worth the effort and the risk. This requires larger brains, like those of the chimpanzee.

The concluding question for Mars addressed the puzzle of the common ancestor for humans  and chimpanzees. Such an animal’s brains would have needed features that are now shared by its descendants: both chimps and humans adapt well to changing environments, are able to use tools and are social. If this is the case, why is one descendant confined to the tropics, while the other spread across the world?

Clever apes cooperating

Slors started his talk by surveying older narratives about the development of human intelligence. In these theories, the ability of humans to cooperate is a result of our intelligence, increasing the chance of survival. One theory sees this intelligence emerging because early humans needed to improvise new strategies and needed to be able to deal with a lot of information at once. Another theory sees social intelligence becoming more important as groups become larger: Understanding the intentions of others and being able to spot deceivers are beneficial to individuals.

According to Slors, the problem with these theories is their conception of individual intelligence. Comparative testing between chimps and humans reveals something strange: On tests that only involve intellectual abilities that are congenital, chimps perform equal to humans. The only tests on which humans excel involve the ability to learn from someone else: social learning. Slors reverses the old narrative to the possibility that our ancestor lived in groups before it became intelligent. The cultural intelligence hypothesis holds that living in groups creates opportunities for apes to mimic each other. Over time, social learning became embedded in their social structure. They gain a form of group intelligence.

Cultural Evolution

When the culture of the group promotes social learning, it becomes possible for knowledge and skills that are discovered by one generation, to be transmitted and preserved to a subsequent one. This is called the ‘ratchet effect’: a social mechanism that prevents new generations from needing to reinvent something that was already discovered, instead allowing them to improve on what they already know. Once the ratchet effect exists, cultural evolution emerges: beneficial ideas and practices are retained and bad ideas die out.

Because the problem solving ability of a group is greater than that of any individual, individuals adapted to group life will be more successful and will have more offspring. Over time, groups will be made up of individuals better suited to group life. Thus they become better at solving problems. Genetic and cultural evolution reinforce each other. The special human intelligence we were looking for is this group intelligence.

Destroying the Planet Is Not Very Clever

In the discussion, Leijenhorst asked Mars if his question about the evolution of our brains is now answered. While Mars considered the cultural intelligence hypothesis functional, it was unclear to him how it could be scientifically tested. Slors and Mars discussed the role of ‘Theory of Mind’ in social intelligence. An experiment suggests that chimps do have Theory of Mind, unlike previous assumptions. Mars suggested that while humans can use Theory of Mind in cooperation, chimps only use it in competitive situations. Slors referred to our ability to divide clear roles. Once we recognise someone’s role, we do not have to wonder what that person wants to do. Mars adds that perhaps Theory of Mind is suitable for small intimate groups, but larger ones require role-based categorization.

A final question came from someone from the audience at home, who asked why animals can live in harmony with nature, while intelligent humans seem unable to. “Yes,” Slors affirmed, “destroying the planet is not very clever”. He considered the suitability of our group intelligence for the size of our societies. We depend on habits and routines that we do not fully understand. We may not be able to teach ourselves the different habits that are required. Mars remarked that animals only appear to live in harmony with nature because of biased sampling: all animals that could not do so, have died out. “What this means for our species,” he concluded, “I will leave up to you.”

This report is written by Thom Janssen as part of the Research Master Philosophy at Radboud University.