The human brain is asymmetric. The structures of the right and left hemispheres do not completely mirror each other. The difference is attributed to structures in the left hemisphere of the brain, specifically two areas called the Broca’s area and the Wernicke’s area located in the frontal and temporal lobes respectively. These two regions are believed to be areas critical to language use and language processing.[74] Damages to these regions, as in the case of patients with global aphasia, severely disrupt the comprehension and production of language.

This connection between the asymmetry of the human brain and the language centers of the human brain gives researchers the needed premise for determining potential language ability in nonhuman primates, using brain anatomy. If they can demonstrate that there is a similar asymmetry in the ape brain, it would imply the existence of the language centers namely Broca’s region and Wernicke’s region. In a paper published in the journal Science in 1998, Patrick Gannon and fellow researchers, examined 18 brains from chimpanzee cadavers to see whether they could detect any asymmetry of the chimpanzee brain. They found that the planum temporale, a key site found within the Wernicke’s area, was larger in the left hemisphere for 17 out of the 18 brains examined, demonstrating an asymmetry of the ape brain. [75] Another paper published in the journal Nature, in 2001, suggests the asymmetry of the Broca’s region in the ape brain. For this experiment Caludio Cantalupo and William Hopkins used MRI scans to study the brains of chimpanzees, bonobos and gorillas. They found that Brodmann’s area 44, a part of the Broca’s region, was larger in the left hemisphere of the ape brains, once again suggesting the asymmetry of the ape brain. [76]

These discoveries give credence to the arguments put forward by those who insist on the continuity of the language mechanism between apes and humans. It does not however under any circumstance end the debate. Perhaps the best argument in the arsenal of those who argue against language in apes, is not the ape language experiments, rather the discrepancy between the documented use of symbolic communication that apes develop on their own in wild or in captivity, and symbolic communication in encultured apes.

There is now extensive documentation of apes developing symbolic communication on their own in the wild and in captivity without human intervention. One of the documented cases involves the gorillas at the San Francisco zoo. Joanne Tamer, who had worked with Koko, was surprised one day to find the gorillas at the zoo, who had not been cross-fostered, use gestures, some similar to those Koko herself used, to systematically communicate with each other. These gestures included, visual, tactile and auditory gestures. [77] Similar gestural communication has been documented among chimpanzee groups in Africa and bonobos. [78] However the total number of such gestures and their use are far more limited when compared to the encultured apes. If apes do have the basic mechanism necessary for symbolic communication, why is it that they do not develop a system of symbolic communication anything like the system encultured apes seem able to learn?