They hear and interpret sounds just as we do, and even think in sentences. But various species of monkeys and apes still aren’t talking, and some scientists now believe it’s because they simply have no pressing reason to speak.
Researchers studying the linguistic faculties of chimpanzees, Diana monkeys and other primates have found an abundance of evidence proving these animals could converse if they wanted to. But the reason for their reticence has long been a scientific mystery.
A recent study by psychologist Klaus Zuberbühler found that Campbell’s monkeys can vary individual calls by adding suffixes, just as humans do.
The monkeys cry out “krak” when they see a leopard but add “-oo” as a generic warning or when they’re repeating leopard warnings they have overheard.
The Campbell’s monkeys can also combine this “krak-oo” call with a “boom” sound to indicate that a tree is about to fall. Other primates have displayed similar abilities to attach different meanings to varying sequences of sounds.
One reason that speech has not yet occurred despite these abilities may be that primates lack a “theory of mind”, meaning they don’t realize that others have thoughts.
But some scientists, including Zuberbühler, argue that because there is no evolutionary pressure for them to communicate using language, their brains simply have not changed over time to allow speech.
Whereas human brains allow interaction between the different neural systems that make language possible, animal brains do not.
“For whatever reason, maybe accident, our brains are promiscuous in a way that animal brains are not, and once this emerges it’s explosive,” says animal communication expert Marc D. Hauser of Harvard University.