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| Macaque monkeys. Think like humans. |
Humans and monkeys have similar thinking patterns, according to research from UC Berkeley, Harvard University and Carnegie Mellon University.
Recursive thinking - a cognitive process of arranging words, phrases or symbols in a way that helps convey complex commands, sentiments and ideas - was thought to be unique to humans - has now been shown to exist in macaque monkeys. This thinking enables us to arrange ideas into nested hierarchies, rather like a linguistic expression of a venn diagram or the nested hierarchies found in cladistics, for example. This ability is crucial to syntax and semantics in human language.
The study showed that the human ability is not conditional on age or cultural environment; nor is it unique to humans.
The Berkeley press release explains:
The study was led by Harvard postdoctoral researcher Stephen Ferrigno, who traveled to Bolivia’s Amazon rainforest where Tsimane’ people practice subsistence farming, and live a traditional lifestyle with relatively little schooling and modern technology.
Ferrigno and fellow researchers sought to analyze what it is about human thinking that sets human and non-human primates apart. While numerous functions are unique to the human brain, we share neural similarities with monkeys, and these latest findings confirm that connection.
Researchers tested the recursive skills of 10 U.S. adults, 50 preschoolers and kindergarteners, 37 members of the Tsimane’ and three male macaque monkeys.
First, all participants were trained to memorize different sequences of symbols in a particular order. Specifically, they learned sequences such as { ( ) } or { [ ] }, which are analogous to some linguistic nested structures.
Participants from the U.S. and monkeys used a large touchscreen monitor to memorize the sequences. They heard a ding if they got a symbol in the right place, a buzzer if they got it wrong and a chime if the whole sequence was correct. The monkeys received snacks or juice as positive feedback.
Meanwhile, the Tsimane’ participants, who are less accustomed to interacting with computers, were tested with paper index cards and given verbal feedback.
Next, all participants were asked to place, in the right order, four images from different groupings shown in random order on the screen.
To varying degrees, the participants all arranged their new lists in recursive structures, which is remarkable given that “Tsimane’ adults, preschool children and monkeys, who lack formal mathematics and reading training, had never been exposed to such stimuli before testing,” the study noted.
“These results are convergent with recent findings that monkeys can learn other kinds of structures found in human grammar,” Piantadosi said.
The results were published open access in Science Advances last Friday:
Abstract
The question of what computational capacities, if any, differ between humans and nonhuman animals has been at the core of foundational debates in cognitive psychology, anthropology, linguistics, and animal behavior. The capacity to form nested hierarchical representations is hypothesized to be essential to uniquely human thought, but its origins in evolution, development, and culture are controversial. We used a nonlinguistic sequence generation task to test whether subjects generalize sequential groupings of items to a center-embedded, recursive structure. Children (3 to 5 years old), U.S. adults, and adults from a Bolivian indigenous group spontaneously induced recursive structures from ambiguous training data. In contrast, monkeys did so only with additional exposure. We quantify these patterns using a Bayesian mixture model over logically possible strategies. Our results show that recursive hierarchical strategies are robust in human thought, both early in development and across cultures, but the capacity itself is not unique to humans.
Stephen Ferrigno, Samuel J. Cheyette, Steven T. Piantadosi, Jessica F. Cantlon.
Recursive sequence generation in monkeys, children, U.S. adults, and native Amazonians.
Science Advances, 2020; 6 (26): eaaz1002 DOI: 10.1126/sciadv.aaz1002
Copyright: © 2020 The authors.
Published by American Association for the Advancement of Science. Open access.
Reprinted under Creative Commons Attribution-NonCommercial 4.0 license (CC BY-NC 4.0)
So, it would seem that our human ability to think recursively - a basic aspect of our ability to form and communicate complex ideas - was present in a common ancestor from our remote simian ancestry some 25 million years ago.
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