Why Can Humans Talk When Most Animals Can’t? Brain ‘Bypass’ Holds a Clue
Neuroscientists have uncovered new insights into a key evolutionary question: Why can humans talk when most animals can’t?
The research, published in the journal Science, was led by Emory University and the New College of Florida.
The findings suggest that seals and sea lions may have vocal flexibility as a side effect of developing a brain “bypass” for voluntary breath control. That same bypass allowed them to adapt to aquatic life.
Comparative Brain Study Reveals Key Differences
The comparative study examined the brains of coyotes alongside those of sea lions, elephant seals, and harbor seals—marine carnivores with varying degrees of vocal control that are evolutionary cousins to canines.
Seals are among the few animal species known to have the super vocal flexibility that allows them to mimic human voices. Sea lions have also demonstrated good vocal plasticity on a more limited scale. The neurobiology of these capabilities, however, was not known.
Researchers used diffusion magnetic resonance imaging (MRI) on postmortem animal brains to view connective neural pathways across species. All brains used in the study came from wild animals that died naturally in rehabilitation facilities or had to be euthanized due to injuries.
How Marine Mammals Developed Vocal Flexibility
In coyotes, the mid-brain—associated with automatic behaviors like breathing, swallowing, and reactions to threats—controls the groups of cells in the brain stem that send signals to muscles used for vocalization.
However, marine mammal brains have a direct connection between the vocal motor cortex and the groups of cells controlling vocal muscles, bypassing the mid-brain region.
Researchers hypothesize that most animals lack vocal flexibility due to their inability to “unlock” this automatic response mechanism from vocalization.
Seals and sea lions have loosened this automatic control through their development of exquisite breathing and swallowing capabilities, allowing them to hunt and eat underwater. Sea lions, for example, can stay underwater for an average of 10-20 minutes, while some seal species can dive without surfacing for up to two hours.
Ecological Recipe for a Vocally Flexible Brain
“We’ve discovered an ecological recipe for how a mammal might evolve a vocally flexible brain,” says Peter Cook, now associate professor of marine mammal science at New College of Florida.
“By broadening the scope and using these neuroimaging techniques to compare more mammalian species wired to have vocal flexibility with those that are not, we might be able to build up an evolutionary tree for language,” adds Gregory Berns, Emory professor of psychology.
Diffusion MRI and Brain Mapping
MRI scans reveal information about the architecture of a brain—known as gray matter. Diffusion MRI provides information about how molecules move through biological tissues, mapping the connective pathways of a brain—known as white matter.
The technique of using diffusion MRI on a non-living brain was developed at the University of Oxford to study Alzheimer’s disease in human brains. Because dead brains don’t move, researchers can acquire extremely high-quality data.
The technique has also been used in some primate and rodent studies. Berns helped pioneer the use of diffusion MRI in a range of other animals, including brains preserved in museum collections. He led a 2017 study that successfully mapped the connectivity in the brains of two extinct thylacines, or Tasmanian tigers, which had been stored in formaldehyde for more than 100 years.
Intelligent Marine Mammals
Cook, who previously studied the neurobiology and behavior of pinnipeds—carnivorous, fin-footed marine mammals—notes that seals and sea lions are often underestimated.
“Many people have an impression of seals and sea lions as just fat, furry slugs, laying on a beach and barking,” Cook says. “In reality, they are intelligent animals with brains close in size to those of chimpanzees.”
He enjoys teaching them hearing and memory tasks, noting their drive to learn and quickness at picking up new behaviors.
Vocal Mimicry in Seals and Sea Lions
Both Berns and Cook were intrigued by the unique vocal capabilities of these marine mammals, which offer a rare opportunity to study vocal dexterity in a non-human animal.
Hoover, a harbor seal who could mimic his keeper’s Boston accent, is a well-known example of this plasticity. Researchers at the University of St. Andrews in Scotland have also trained gray seals to imitate human voices humming “Twinkle, Twinkle Little Star” and the theme to Star Wars.
Future Research
The researchers are building on these findings through a similar brain study in whales, dolphins, and porpoises, another group of marine mammals with impressive vocal abilities.
“All animals can learn,” Cook says. “And almost all birds and mammals communicate with their voices. The paradox of why so few animals can learn to control their calls is an irresistible scientific mystery.”
Source: Emory University
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