In a major contribution to understanding the evolution of human cognition, bonobos (also known as pygmy chimpanzees) have demonstrated the ability to create mental images of pretend scenarios. This suggests that the common ancestor of humans, chimpanzees, and bonobos (a separate species but closely related to chimpanzees) had the forerunners of abstract symbolic thinking. Their common ancestor is thought to have lived between 6 and 9 million years ago.
New research “Evidence of object pretending by the language-trained bonobo Kanji” was published in a magazine science.
The male bonobo, known as Kanji, had lived at a research center in Iowa for years, but was already famous for displaying an uncanny ability to learn and communicate with human researchers using sign language and a special keyboard. In a recent series of three experiments, Kanzi demonstrated that he can distinguish between spurious and real objects and that he can retain abstract representations of external phenomena in his mind even when their original configuration changes.
The three experiments are:
1) The first was a pretend tea party where researchers poured liquid from an empty pitcher into two empty glasses, pretended to “pour” one of the empty glasses into the pitcher, and replaced the “empty” glass next to the “full” glass. Kanzi was then prompted to point to the glass, which still contained the fake liquid. He chose the correct one more than two-thirds of the time. This was much more frequent than chance.
2) As a control, the researchers conducted another experiment in which there were two glasses, one filled with juice and one empty. The researchers then pretended to pour water from an empty pitcher into each glass. Kanzi picked up a glass of real juice more than three-quarters of the time, demonstrating that she understood the difference between reality and imagination.
3) As an additional control, using two transparent cups, the researchers placed a grape in one cup and recreated the behavior by pretending to place a grape in the second cup. Kanzi chose the cup with grapes more than two-thirds of the time.
The authors explain the significance of their experimental results as follows:
In the context of pretending, individuals need to form second-order representations that are imagined or simulated states (“pretend there is tea in one cup”) that are separated from real representations (“both cups are empty”) so as not to confuse the two. A situation thus becomes linked to two simultaneous representations: a primary representation representing the current state of the world and a secondary representation representing another state of affairs. Therefore, second-order representation is thought to involve cognitively separating, or isolating, the imagined mental model from the opposite model of reality directly perceived by the mind.
This points to a fundamental foundation of human cognition, the authors argue.
Although the cognitive mechanisms that enable second-order representations are still poorly understood, they serve as a fundamental prerequisite not only for pretending but also for several other abilities proposed to be unique to humans, such as reasoning about mutually exclusive possibilities, imagining possible futures, causal inference, and tracking the mental states (e.g., beliefs) of others.
Although it has long been known that great apes can plan ahead and consider the beliefs of other individuals, there has been no reproducible evidence of their ability to engage objects in pretend play.
The authors say previous observations suggesting that apes had some ability to distinguish between pretend and reality, such as adults holding sticks as if they were infants, dragging imaginary blocks across the floor, or appearing to eat blueberries from printed photographs, could have been interpreted differently, such as by simple replication of learned behaviors. They believe the new controlled experiment provides a stronger basis for their conclusions.
They also consider the possibility that captive apes that received communication training (sign language or use of keyboard symbols) developed enhanced skills not seen in wild populations. The researchers conclude that further studies comparing wild and “civilized” populations are needed. Even if training is a factor, it is important that the potential for such behavior exists, even in rudimentary forms in the wild. This raises the question of what selective advantage could be gained by wild populations with such potential.
The authors propose that “second-order representations underlie many other complex cognitive abilities, such as imagining future possibilities and attributing mental states.” These, in turn, form the basis for the development of abstract symbolic thinking, and thus the basis of human culture.
Abstract symbolic thinking represents a decisive qualitative leap in the evolution of human cognition. It is the ability to form and manipulate symbols (patterns, sounds, marks, gestures) that represent objects, relationships, and ideas that do not immediately exist. This ability is the basis of language, technology, art, and social organization. It is therefore central to the emergence of culture, cooperative labor, and the collective understanding necessary for conscious political action.