Chimpanzees learn new words for objects from their peers. When a group of captive Dutch chimpanzees joined a group of chimps in Edinburgh, the Dutch chimpanzees picked up the Edinburgh dialect (specifically, the call that indicates "apples") over a three year period. During that time, the two groups also formed social connections and became friendly, which was likely the impetus for a common language.

What's more, this provides crucial new information about the structure and development of "referential calls," or sounds that indicate, for example, food type. Many have argued that animal grunts and chirps about food tend to reveal only excitement level, and that variation in vocalizations correlates with variation in preference. Indeed, before the two chimpanzee groups mixed, the Dutch chimpanzees -- who love apples -- used an excited high-pitched call, while the Edinburgh chimps -- who were not crazy about apples -- used a low grunt. But over time as the groups mixed, the Dutch chimpanzees retained their passion for apples but adopted the Edinburgh low-pitched grunt to refer to the tasty fruit.

Thus, it is clear that referential calls-- a recognized precursor of language development-- are about more than just excitement level; further, chimps learn and adopt new calls when social groups mingle. What does this mean? In our ape relatives (and thus likely our ape ancestors), vocalized "words" for objects are not just a manifestation of arousal, but instead serve a more complex linguistic and social purpose.

Piece by piece, we are uncovering evidence about the development of the most important human trait: complex, abstract language.

Many thanks to Elliott Bannan for sending along this article!