Scientists Find Crows Are Capable of Recursion — A Cognitive Ability Thought to Be Unique to Humans and Other Primates

According to a new study, crows possess the cognitive ability for one of the linguistic elements that make human language so complex.

In the early 2000s, Noam Chomsky and other linguists thought that if there was one thing that belonged specifically to human language, it was recursion, and that this was what distinguished human language from animal communication. As it turns out, this is not the case: a 2020 study proved that rhesus monkeys can do the thing too, and a newly published study shows that crows can also do recursion. 

OK, so what’s recursion? It’s the capacity to recognize paired elements in larger sequences – something that has been claimed as one of the key features of human symbolic competence. Consider this example: “The rat the cat chased ran.” Although the phrase is a bit confusing, adult humans easily get that it was the rat that ran and the cat that chased. Recursion is exactly this: pairing the elements “rat” to “ran” and “cat” to “chased”. 

Put somewhat more simply, similarly to humans monkeys and crows can recognize that a structure can contain other structures with meaning. But for decades scientists thought that humans, or at least primates, are the only animals capable of understanding recursion. 

Yet, following the discovery, about two years ago, that rhesus monkeys can understand the idea of recursion on a par with three- to four-year-old human children (albeit with some extra training), a team has now conducted similar experiments with crows, and they turned out to outdo monkeys in certain aspects!
Researchers from the University of Tübingen have studied crows using the same method as their colleagues used in the previous Wisconsin study with monkeys. In this one, the animals had to find a pair of symbols in a sentence of symbols, so they had to find out, for example, where in the <()> symbol sequence the pair of brackets was located.

When they did, the researchers created longer and longer sentences to see if the test subjects would still pick out the embedded ones. As with the rhesus monkeys, the subjects could pick out the embedded characters in 40% of trials, but without the extra training that the monkeys received! 

So, recursive capabilities are not limited to the primate genealogy, as it turns out. Which also helps reiterate just how smart crows are.


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