Human evolution; our complex speech mechanism (Introduction)

by David Turell @, Wednesday, February 27, 2019, 05:19 (234 days ago) @ David Turell

Some animals can mimic our speech but only humans have coordinated speech and language:

https://www.knowablemagazine.org/article/mind/2019/why-speech-human-innovation

"It’s true that humans, and humans alone, evolved the complex set of voice, hearing and brain-processing skills enabling full-scale sophisticated vocal communication. Yet animals can make complicated sounds; parrots can mimic human speech and cats can clearly convey that it’s time for a treat. Many animals possess an acute sense of hearing and are able to distinguish random noises from intentional communication. So even though only humans possess the complete linguistic package, the components of language ability “have very deep evolutionary roots,” says Fitch, of the University of Vienna.

"Much of the physiological apparatus for hearing and speaking is found in all land-dwelling vertebrates — the tetrapods — including mammals, birds, amphibians and reptiles. “Humans share a significant proportion of our basic machinery of hearing and vocal production with other tetrapods,”

"Life-forms occupying numerous branches of the tree of life possess anatomical tools for producing and perceiving vocal communication. Where human ability exceeds our predecessors, Fitch says, is the sophistication of the brain circuitry adapted to the uniquely human capacity for complex linguistic expression.

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"Among the tetrapods, mammals evolved much more sensitive hearing, able to cope with a wider range of frequencies and therefore more able to process nuances of vocalizations. Humankind’s primate ancestors, for instance, possessed highly capable hearing ability. “There is nothing about the human ear that is strikingly different from that of other primates,” Fitch writes. “Our peripheral hearing apparatus was in place, in our primate ancestors, in essentially modern form long before we evolved the capacity for speech.”

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"Besides all that, parrots and many other bird species, some bats and even elephants can mimic vocal sounds. So humans’ distinctive speech can’t depend solely on vocal production ability. Considering all the evidence, the vocal and auditory skills of various animals tell a tale of multiple preludes to the human speech story. That tale reveals that humans acquired speech not via anatomical innovation for vocalizing and hearing, but by novel neural connections that control the anatomical hardware.

"After all, speech requires more than producing and perceiving sounds. A speaker’s brain must decide what sounds to produce and issue instructions for producing them to the body’s vocal apparatus. And a listener’s brain must be able to decode auditory signals it receives and then issue commands for a vocal response. People are skillful at producing sounds in response to other sounds — it’s why you can repeat a word out loud after the first time you hear it.

"Such controlled vocalization of a word is different from just making noise. Most animals possess neural circuitry for producing “innate” vocalizations: Dogs bark, squirrels chatter and seagulls squawk. Even humans have their own innate vocalizations, including crying, laughter and screams. But among primates, only humans have the “capacity to produce novel, learned vocalizations beyond the innate call repertoire,” Fitch notes.

"Today the dominant hypothesis explaining that ability is the presence of special connections between brain regions involved in controlling speech and hearing. Innate calls — in humans and all other mammals — are initiated by direct signals from the brain stem. Indirect messaging from the cortex (the brain’s more advanced outer layer) enables voluntary suppression or production of innate calls. Unlike other animals, humans possess direct connections between nerve cells in the cortex and the nerve cells that control the muscles operating the larynx. Some apes and monkeys have direct connections from cortex to the muscles controlling the lips and tongue, but not to the muscles controlling the larynx. (Circuitry connecting the auditory cortex to the motor cortex also seem more extensively developed in humans.)

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“'The genetic underpinnings of … [neural] connections involved in human vocal control are virtually unknown,”

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“'Language is more than speech,” said Friederici, director of the Max Planck Institute for Human Cognitive and Brain Sciences, in Leipzig, Germany. “Speech … uses a limited set of vowels and consonants to form words. Language, however, is a system consisting of words … and a set of rules called grammar or syntax to form phrases and sentences.”

"Nonhuman primates can learn the meaning of individual words, she notes, but aren’t capable of combining words into meaningful sequences of any substantial length. That ability also depends on circuitry connecting different parts of the brain, current research by Friederici, collaborators and other scientists is now showing.

"Understanding that circuitry depends on comparing the cellular architecture and nerve fiber tracts of the human brain with the brain of animals with lesser linguistic power. So in a way, scientists may be able to ask animals for clues not only to the evolution of speech, but to language skills more generally as well. Sort of like going straight to the source and asking the horse."

Comment: As usual we are different in kind, not degree, as vocal animals have lots of the parts we have but not the brain controls.


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