What Makes a Brain “Speech Ready?”

crab-eating macaque monkey
Crab-eating macaque (Macaca fascicularis) in Lopburi, Thailand
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Can monkeys talk? According to new research, they could—if their brains would let them. Monkeys apparently have the appropriate architecture for speech; their including vocal chords, larynx, mouth, and tongue could theoretically produce enough consonants and vowels for true speech. A monkey brain, however, is not properly set up to talk. So what is required for functioning speech?

Language development begins almost immediately after birth. There are two areas in particular, Broca’s area in the frontal lobe and Wernicke’s area in the temporal lobe, that are associated with language processing. Apes have comparable, though less-developed, regions in their own brains. The angular gyrus, a region located in the parietal lobe, also seems to be connected to cognition, memory retrieval, and other processes associated with language. Sophisticated neural connections are also required to connect these different processes. Scans of readers, however, showed increased blood flow across a wide swath of the brain, suggesting that understanding sentences in particular may require a lot more than just the speech and language centers of the brain.

There is a school of thought that language evolved more from gestures than sounds. 

Humans (like apes and monkeys) are a very visual species, and there seems to be a clear connection between speech comprehension and visual processing. Studies of both children and adults show that the areas of the brain activated during speech are different when a subject is able to hear and see the speaker. Accordingly, connected audio and visual sections of the brain seem to be involved in true comprehension.

A speculative article in American Scientist pursues a possible explanation. There is a school of thought that language evolved more from gestures than sounds. If so, then the visual component of language comprehension may be even more important than the auditory. Bipedalism helps a lot in the development of gestural language—monkeys, for example, need their hands for grasping and have less opportunity to use them for signaling.

Gestural language evolution is not universally accepted, but it is plausible. Hand signals would have been extremely useful for gregarious species like early hominids, and silence is helpful under many cooperative activities such as hunting. Studies of people who rely on sign language for communication show that similar areas of the brain are activated as in verbal speech, so the brain wiring is clearly there. Almost everyone accompanies speech with gesturing to accentuate his or her meaning.

For a monkey, a simple communication, i.e. a call that says “lion!” might be sufficient for their needs. A complex thought like “Lions are jerks” might be overkill—all the monkey really needs to know is that it’s time to take cover. Humans have more complex thoughts to convey, and have evolved a brain to handle the task.


JSTOR Citations

Behavior

Science News, Vol. 152, No. 19 (Nov. 8, 1997), p. 297

Society for Science & the Public

The Processing of Audio-Visual Speech: Empirical and Neural Bases

By: Ruth Campbell

Philosophical Transactions: Biological Sciences, Philosophical Transactions: Biological Sciences, Vol. 363, No. 1493, The Perception of Speech: From Sound to Meaning (Mar. 12, 2008), pp. 1001-1010

Royal Society

The Gestural Origins of Language: Human language may have evolved from manualgestures, which survive today as a "behavioral fossil" coupled to speech

By: Michael C. Corballis

American Scientist, Vol. 87, No. 2 (MARCH-APRIL 1999), pp. 138-145

Sigma Xi, The Scientific Research Society

James MacDonald

James MacDonald received a BS in Environmental Biology from Columbia and a PhD in Ecology and Evolution from Rutgers University, spending 4 years in Central America collecting data on fish in mangrove forests. His research has been published in scholarly journals such as Estuaries and Coasts and Biological Invasions. He currently works in fisheries management and outreach in New York.

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