New research has found that chimpanzees and marmoset monkeys can understand a fundamental rule in complex language-like constructions, suggesting that some of the cognitive elements for understanding language evolved around 40 million years ago when we shared a common ancestor with these primates.
This is certainly not to say that ape-like animals were nattering away many millions of years ago, but it does suggest that the brains of our evolutionary ancestors possessed some of the vital raw materials needed to understand language-like patterns, even long before human language evolved.
The new research, reported in the journal Scientific Advances, looked at the ability to understand “nonadjacent dependencies,” a critical cognitive facilitator of language that involves the ability to understand the relationship between the words in a sentence, even if they are separated by other parts of the phrase. For example, in the phrase “the dog that scared the cat ran away,” we understand that “dog” is linked to “ran away,” even though these components are separated. Humans are able to make this link and it's a crucial part of what makes our languages so complex, not just basic grunts.
The question is: Where did this skill come from? And can it be found in any of our closest evolutionary relatives?
Researchers from the University of Zurich in Switzerland tested whether chimpanzees and common marmosets have any grasp of nonadjacent dependencies. Of course, these species do not speak English or any language, so the team had to devise an experiment using artificial grammar to find out.
They started by teaching the different species that certain sounds were always followed by other specific sounds (for example, a sound “B” always follows sound “A”). In patterns that simulated human language, they were also taught that the two sounds were still linked even if they sometimes were separated by another sound (for example, if “A” and “B” were separated by an “X”).
With this as their foundation, they then played sound combinations that broke the previously learned rules and noted how the animals showed behavioral changes. For example, whenever the rule was violated, the animals would look at the loudspeaker emitting the sounds for much longer than they did after hearing familiar combinations of sounds that stuck to the rules. The researchers attributed this to some sense of surprise or confusion as if they were aware of the “grammatical error."
As the study notes, the ability to keep track of these rules and the dependencies between words is a taxing task on the brain that requires a fair amount of cognitive skills. Despite this, it’s now known that this crucial cognitive ability is found in a select few of our primate cousins and is likely to exist in many more. Since marmosets branched off from humanity’s ancestors around 40 million years ago, it’s also fair to suggest that the skill thus developed around this time.
“The results show that all three species share the ability to process non-adjacent dependencies. It is therefore likely that this ability is widespread among primates,” Professor Simon Townsend, study author at the Department of Comparative Language Science of the University of Zurich, said in a statement. “This suggests that this crucial element of language already existed in our most recent common ancestors with these species.”