Human evolution; our complex speech mechanism, 3 (Introduction)

by David Turell @, Wednesday, July 04, 2018, 00:04 (168 days ago) @ David Turell

Mutation changes:

"One key contributor to the evolution of human speech is the FOXP2 transcription factor. Humans, Neanderthals, and Denisovans share a mutation in the gene for FOXP2 that nonhuman primates lack. Early evidence of FOXP2’s role in human speech and language comes from studies of the KE family, a large extended family living in London in the second half of the 20th century. Some members had only one copy of FOXP2 and had extreme difficulty talking; their speech was unintelligible, and problems extended to orofacial motor control. They also had difficulties forming and understanding English sentences.

"The importance of FOXP2 has been further confirmed by knock-in mouse studies. When the human version of the gene for the FOXP2 transcription factor is inserted into mouse embryos, the animals exhibited enhanced synaptic connectivity and malleability in cortical–basal ganglia neural circuits that regulate motor control, including speech. The evolution of these circuits appears to have a deep evolutionary history going back to the Permian age, 300 million years ago. Avian versions of the FOXP1 and FOXP2 transcription factors act on the basal ganglia circuits involved when songbirds learn and execute songs.

"Exactly how the brain dictates the movement of the vocal tract to produce speech remains murky. Many studies have shown that “matrisomes” of neurons in the motor cortex are instruction sets for the motor commands that orchestrate a learned act. Assemblies of neurons in the motor cortex are formed when a task is learned, and these assemblies guide coordinated muscle activity. To sip a cup of coffee or type at a keyboard, for example, hand, arm, wrist, and other movements are coded in matrisomes. Similar matrisomes likely govern the muscles that move the tongue, lips, jaw, and larynx and control lung pressure during speech, but researchers are just starting to explore this idea. In short, brains and anatomy were both involved in the evolution of human speech and language.

"In 1971, Yale’s Edmund Crelin and I published our computer modeling study of a reconstructed Neanderthal vocal tract.14 We concluded that Neanderthals had vocal tracts that were similar to those of newborn human infants and monkeys and hence could not produce the quantal vowels [a], , and . However, the available archaeological evidence suggested that their brains were quite advanced, and that, unlike monkeys, they could talk, albeit with reduced intelligibility. We concluded that Neanderthals possessed both speech and language. In short, current research suggests a deep evolutionary origin for human language and speech, with our ancestors possessing capabilities close to our own as long as 300,000 years ago.

"Speech is an essential part of human culture, and thus of human evolution. In the first edition of On the Origin of Species, Darwin stressed the interplay of natural selection and ecosystems: human culture acts as an agent to create new ecosystems, which, in turn, directs the course of natural selection. Language is the mechanism by which the aggregated knowledge of human cultures is transmitted, and until very recent times, speech was the sole medium of language. Humans have retained a strange vocal tract that enhances the robustness of speech. We could say that we are because we can talk. "

Comment: Different folks do very different things with their languages which shows how flexible the speech mechanism can be: Hawaiian has almost no consonants, just 'l' and 'k'. In the Kalahari of Africa the bushmen use a click language. About 7,000 languages are recognized! The last paragraph indicates that we are much more than primates from a functional standpoint. We may look like apes, but the relationship stops there. Please read the whole article for deeper appreciation of my point: we are tremendously different in kind.


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