They may not always show it, but new research, published in the journal Science Advances, suggests that non-human primates, even monkeys down on the food chain, have the vocal anatomy to produce clearly intelligible human speech. The discovery negates a long-standing theory that monkeys, gorillas, chimps and the like do not talk as we do because they are incapable of creating the sounds required for the skill.
"I hope that this new data dispels forever the widespread myth that monkeys and apes cannot speak because of anatomical limitations of their vocal tract," lead author Tecumseh Fitch of the University of Vienna's Department of Cognitive Biology told Seeker.
Fitch, senior author Asif Ghazanfar, Bart de Boer and Neil Mathur investigated the range of movements that primate vocal anatomy could produce. Using X-ray videos, they captured and then traced the movements of a macaque's tongue, lips, larynx and more as the monkey vocalized, ate and made facial expressions. The researchers then used these X-rays to build a computer model of a monkey vocal tract, allowing them to answer the question: What would monkey speech sound like, if a human brain were in control?
You can hear the results, first with the monkey model saying, "Will you marry me?" and then, "Joyeux Noel (Merry Christmas in French)."
(Recordings courtesy of Asif Ghazanfar, Princeton Neuroscience Institute; Image 1 Credit: Paul Asman and Jill Lenoble, Flickr; Image 2, showing Tecumseh Fitch in his lab: University of Vienna)
First, Fitch and his team believe that most mammals possess flexible, speech-ready vocal tracts. He said, "It seems clear that this type of flexibility evolved early on, for reasons other than vocalization, probably initially for food processing—manipulating and swallowing food."
He suspects that humans evolved at least two important changes to our brains that give us a communication edge.
Fitch explained, "We have direct connections between our motor cortical neurons and the neurons that actually control the vocal tract musculature, particularly those in charge of the larynx; and we have much more substantial connections, within our cortex, between the auditory cortex—responsible for hearing sounds—and the motor cortex, responsible for making sounds."
Fitch says there are many theories attempting to explain how humans evolved both the brain and the vocal tract for speech. One of his favorites was formulated by famed British naturalist Charles Darwin, who theorized that our ancestors initially evolved to become "singing apes," or kind of a cross between gibbons and songbirds and being able to learn new songs. This musical ability, Darwin suspected, emerged first, and then later was put to use in speech.
|X-ray of a macaque vocal tract.|
Laurie Santos, a psychology professor at Yale University, told Seeker the paper "opens whole new doors for finding the key to the uniqueness of humans' unparalleled language ability."
On the other hand, Constance Scharff, a professor in the Department of Animal Behavior at Free University Berlin, indicates we may undervalue the communicative skills of animals, many of which—like parrots—are clearly very vocal.
Scharff told Seeker that she is glad the new study "puts another nail in the coffin of the idea that the absence of speech in macaques cannot be explained by an unsuitable vocal tract." Scharff also agrees that monkeys "do not seem to have the same regions and neural connections in their brains that humans use."
But, she quickly added, "there are other ways imaginable to achieve speech." She pointed out that parrots, seals and elephants either use quite different brain regions to vocalize, or the underlying systems remain largely unknown.
Read more at Discovery News