From where to what language evolution theory

A recent paper published by the peer review publication platform F1000r delineates a course for the development of yes-no conversations in early Hominans (members of the genus Homo) from vocal ape communication. (for a video presenting the model see https://www.youtube.com/watch?v=AFx3PFtXlns)
Based on reports of signing apes focusing in their spontaneous communication on observations and lack of reports of them using question signs, the author argues that throughout early human evolution we transitioned from curiosity towards items that are present in our immediate environment (observational statements) to items that are absent in our immediate environment (WH questions). This curiosity towards the unknown is the reason our species migrated to every corner in our planet and is the core motivation behinds our species’ quest of scientific exploration and technological development.
The model is primarily based on neuroanatomical comparisons between the brains of monkeys and apes to humans. In all primates, two processing pathways were identified between the auditory cortex and frontal lobe. The auditory ventral stream (AVS), which courses through the temporal pole, is responsible for sound recognition. On the other hand, the auditory dorsal stream (ADS) courses through the parietal lobe and is responsible for sound localization. In humans, however, the ADS has been recently shown to also process speech repetition and speech production. In accordance with the “From Where To What” model, this dual role of the ADS indicates that speech production likely emerged from sound localization.
The relationship between the two evolutionary courses (transitioning from curiosity towards what is present to what is absent and transitioning sound localization to speech production) is explained by analyzing additional roles of the ADS. The model provides evidence that in both monkeys and humans sound localization occurs by providing visual localization centers in the parietal lobe with auditory input. It also shows that in addition to sound localization, the ADS is responsible for voice recognition and integration of faces with their calls. Based on these additional roles of the ADS, the author argues that the original role of the ADS is the recognition and response to contact calls, which were exchanged between mothers and their infants. This exchange of calls allowed mothers and infants to localize each other in times of separation, which were more common once the mother’s hands were occupied with tool using (as previously proposed by the ‘put the baby on the side’ theory). The ADS worked in several stages: detecting the mother/infant’s voice, localizing the voice, determining that the face of the speaker is absent in the location of the voice and finally, emitting a contact call in return. In accordance with the model, the first question ever asked was therefore “Mother/baby, where are you?” and curiosity towards the unknown began by infants and mothers seeking to reunite.
The model then describes a course for the development of speech production/repetition. Based on reports of apes with rudimentary ability to enrich innate calls with intonations and neuroanatomical evidence for direct connection between the frontal lobe and speech centers in the brain stem, the model suggests that early Hominans were capable of modifying their contact calls with intonations. Moreover, based on paleontological evidence in the skull of early Hominans (Homo habilis) for enlargement of the ADS, the author argued that the ADS duplicated resulting with early Hominans having two ADSs. Because the second ADS was closer to the auditory cortex it received primarily input from the auditory cortex (instead of visual input from the visual cortex) and was possibly capable of discriminating calls with different intonations.
The author argues that the two developments enabled lost infants of early Hominans to emit either low or high level distress contact calls. Consequently, their mothers could tell if their infant is in danger and they need to drop what is in their hands and rush towards the infant or just emit a call in return to let them know they are not alone. This use of intonations for signaling different levels of safety is preserved in the ability of present-day infants of modifying the call for their mother with intonations to signal if they are scared (MOMMY!!!) or lonely (Mommy?). It could also be the reason that in most contemporary languages we use different intonations to convert a word into a question (low level distress) or command (high level distress).
By developing ability to choose whether to emit high or low distress level calls, early Hominans acquired the ability to participate with yes-no question answer conversations. For example, an infant could have approached a berry bush and emit a low level distress call (question) and the mother could have responded with a high level distress call (danger) or a low level distress call (safety).
As Hominans practiced these proto-conversations, the ADS gradually acquired more and more volitional control over the vocal apparatus (lips, tongue, vocal folds). As vocal control became more volitional, mothers became capable of associating individual objects in their environments with specific sets of intonations, and infants started to mimic these calls. This is the reason present day infant constantly mimic their parents’ vocalizations. The ability to mimic calls, marked the transition from infants asking their mothers the question “Is it safe?” to “What is it called?”. As time passed these Hominans were capable of memorizing a large vocabulary of nouns, which was the infrastructure for the development of complex language.

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