A new study made public on Sunday suggests that animals, especially mammals, evolved some of the skills underlying the use and development of language long before language itself ever evolved, the researchers said.
It is the first time an animal other than a human or monkey has been shown to have this skill.
“These findings have remarkable parallels with data from human adults, human newborns, and cotton-top tamarins,” the researchers wrote in their report, published in the Journal of Experimental Psychology: Animal Behaviour Processes, which is published by the American Psychological Association.
For their study, neuroscientists Juan Toro and colleagues at Barcelona’s Scientific Park tested 64 adult male rats.
They used Dutch and Japanese because these languages were used in earlier, similar tests, and because they are very different from one another in use of words, rhythm and structure.
The rats were trained to respond to either Dutch or Japanese using food as a reward.
Then they were separated into four groups – one that heard each language spoken by a native, one that heard synthesised speech, one that heard sentences read in either language by different speakers and a fourth that heard the languages played backwards.
Rats rewarded for responding to Japanese did not respond to Dutch and rats trained to recognise Dutch did not respond to spoken Japanese.
The rats could not tell apart Japanese or Dutch played backwards.
What to conclude
“Results showed that rats could discriminate natural sentences when uttered by a single speaker and not when uttered by different ones, nor could they distinguish the languages when spoken by different people,” the researchers wrote.
Human newborns have the same problem, although tamarins can easily tell languages apart even when spoken by different people, the researchers said.
“It was striking to find that rats can track certain information that seems to be so important in language development in humans,” Toro said.
The study shows “which abilities that humans use for language are shared with other animals, and which are uniquely human. It also suggests what sort of evolutionary precursors language might have”, he added.