For the first time ever, animals have been observed changing their call for a particular object — something comparable in human language to a noun. The new research overturns the previous understanding of these vocalizations as essentially fixed.

"As far as we know, this is the first evidence we've seen of a referential call being modified," says Simon Townsend, lead author of the paper published in the journal Current Biology and head of the University of Zurich's animal communication group. "This suggests that the way meaning is assigned in human language and in animals might be more similar than previously thought."

The chimpanzees' vocalizations expressed their feelings on apples

Scientists observed the change during the integration of two groups of adult chimpanzees in 2010. Seven individuals from Beekse Bergen Safari Park in the Netherlands were moved in with six residents of Edinburgh Zoo in the UK, something that would be extremely unlikely to occur in the wild since the primates tend to be territorial. Researchers took advantage of this rare event to record the grunts of the two groups in response to an item of food before and after the move. In this case the item was an apple, and one group of chimps liked the fruit better than the other.

"The Edinburgh chimps didn’t really like apples and gave noisy, rough grunts when they ate them," says Townsend. "But the other group [from the Netherlands] really liked them and were happier when they ate them, producing high-pitched, excited, happier sounds." After the social integration was complete — that took a year or so — the immigrant group of chimps changed their vocalization to mimic the lower, rougher grunts of their hosts. Despite this change in vocalization, though, the Dutch chimps' enjoyment of apples remained the same — a fact established using simple preference tests where the chimps were offered a selection of food to choose from.

the study shows the chimps' vocalizations are more than just automatic responses

This last fact is what makes the observations so significant, says Jacob Dunn of the University of Cambridge, a researcher in primate communication. Though previous research has shown that calls can be modified, today's study suggests that the meaning behind the vocalizations has been made abstract in some way and divorced from the animal's emotional reaction, Dunn says. "It's not something entirely novel or new," Dunn told The Verge. "But it definitely takes a step forward in what we know and brings further evidence to show that primates are probably more flexible than we imagine."