Is the ability to learn language as unique to humans as people have always assumed? Or is it possible that other primates, such as chimpanzees, also have language?
Chimpanzees possess a brain structure resembling a similar area in the human brain that is thought to control language, according to a study published in the January 9, 1998, issue of Science. Experts said the study challenged long-held assumptions about the evolution of language in humans and raised new questions about the ability of chimpanzees to communicate.
The human brain generally exhibits a slightly enlarged area in the left hemisphere called the planum temporale (PT), a structure apparently involved in the processing of visual symbols and speech. Since the 1960s scientists have argued that the PT was necessary for language and may even constitute a uniquely human evolutionary adaptation. The new study is the first to demonstrate that the structure exists in another species, the chimpanzee.
Researchers measured the right and left hemispheres of 18 chimpanzee brains and found the enlarged area to be present in 17 of the specimens. In contrast, studies of human brains have shown that 7 out of 10 humans display an enlarged PT. The existence of the PT in both humans and chimpanzees provides strong evidence that the structure existed in a common ancestor of both species some 8 million years ago, the study reported.
Since chimpanzees do not appear to have developed language, the study authors suggested the finding could mean three distinct things. First, the PT in the common ancestor may have been unrelated to language functions but later evolved to fulfill those tasks in humans alone.
Second, the ancestral PT may have evolved to serve language functions, but followed separate trajectories in humans and chimpanzees. Humans developed spoken and sign languages. This raises the possibility that chimpanzees may have developed a form of gestural-visual communication that is yet to be understood, the researchers said.
Finally, it is possible that the PT is tangentially, but not directly, related to language functions in either humans or chimpanzees. Instead, the structure may be involved in unknown functions that are common to both species, the study said.