Recursive language and modern imagination were acquired simultaneously 70,000 years ago

Summary: A mathematical model suggests a genetic mutation which extended the critical period by slowing prefrontal cortex development in two or more children 70,000 years ago was one factor for the emergence of recursive language and modern imagination.

Source: Pensoft Publishers

A genetic mutation that slowed down the development of the prefrontal cortex (PFC) in two or more children may have triggered a cascade of events leading to acquisition of recursive language and modern imagination 70,000 years ago.

This new hypothesis, called Romulus and Remus and coined by Dr. Vyshedskiy, a neuroscientist from Boston University, might be able to solve the long-standing mystery of language evolution. It is published in the open-science journal Research Ideas and Outcomes (RIO).

Numerous archeological and genetic evidence have already convinced most paleoanthropologists that the speech apparatus has reached essentially modern configurations before the human line split from the Neanderthal line 600,000 years ago. Considering that the chimpanzee communication system already has 20 to 100 different vocalizations, it is likely that the modern-like remodeling of the vocal apparatus extended our ancestors’ range of vocalizations by orders of magnitude. In other words, by 600,000 years ago, the number of distinct verbalizations used for communication must have been on par with the number of words in modern languages.

On the other hand, artifacts signifying modern imagination, such as composite figurative arts, elaborate burials, bone needles with an eye, and construction of dwellings arose not earlier than 70,000 years ago. The half million-year-gap between the acquisition of the modern speech apparatus and modern imagination has baffled scientists for decades.

While studying acquisition of imagination in children, Dr. Vyshedskiy and his colleagues discovered a temporal limit for the development of a particular component of imagination. It became apparent that modern children who have not been exposed to full language in early childhood never acquire the type of active constructive imagination essential for juxtaposition of mental objects, known as Prefrontal Synthesis (PFS).

Dr. Vyshedskiy explains:

“To understand the importance of PFS, consider these two sentences: “A dog bit my friend” and “My friend bit a dog.” It is impossible to distinguish the difference in meaning using words or grammar alone, since both words and grammatical structure are identical in these two sentences. Understanding the difference in meaning and appreciating the misfortune of the 1st sentence and the humor of the 2nd sentence depends on the listener’s ability to juxtapose the two mental objects: the friend and the dog. Only after the PFC forms the two different images in front of the mind’s eye, are we able to understand the difference between the two sentences. Similarly, nested explanations, such as “a snake on the boulder to the left of the tall tree that is behind the hill,” force listeners to use PFS to combine objects (a snake, the boulder, the tree, and the hill) into a novel scene. Flexible object combination and nesting (otherwise known as recursion) are characteristic features of all human languages. For this reason, linguists refer to modern languages as recursive languages.”

Unlike vocabulary and grammar acquisition, which can be learned throughout one’s lifetime, there is a strong critical period for the development of PFS and individuals not exposed to conversations with recursive language in early childhood can never acquire PFS as adults. Their language is always lacking understanding of spatial prepositions and recursion that depend on the PFS ability. In a similar manner, pre-modern humans would not have been able to learn recursive language as adults and, therefore, would not be able to teach recursive language to their own children, who, as a result, would not acquire PFS. Thus, the existence of a strong critical period for PFS acquisition creates a cultural evolutionary barrier for acquisition of recursive language.

This shows an ancient statue of a lion man
The lion-man sculpture from Germany (dated to 37,000 years ago) must have been first imagined by the artist by mentally synthesizing parts of the man and beast together and then executing the product of this mental creation in ivory. The composite artworks provide a direct evidence that by 37,000 years ago humans have acquired prefrontal synthesis. The image is credited to J Duckeck.

The second predicted evolutionary barrier was a faster PFC maturation rate and, consequently, a shorter critical period. In modern children the critical period for PFS acquisition closes around the age of five. If the critical period in pre-modern children was over by the age of two, they would have no chance of acquiring PFS. A longer critical period was imperative to provide enough time to train PFS via recursive conversations.

An evolutionary mathematical model, developed by Dr. Vyshedskiy, predicts that humans had to jump both evolutionary barriers within several generations since the “PFC delay” mutation that is found in all modern humans, but not in Neanderthals, is deleterious and is expected to be lost in a population without an associated acquisition of PFS and recursive language. Thus, the model suggests that the “PFC delay” mutation triggered simultaneous synergistic acquisition of PFS and recursive language.

This model calls for:

  • two or more children with extended critical period due to “PFC delay” mutation;
  • these children spending a lot of time talking to each other;
  • inventing the recursive elements of language, such as spatial prepositions;
  • acquiring recursive-conversations-dependent PFS;
  • eaching recursive language to their offsprings.

The hypothesis is named after the celebrated twin founders of Rome, Romulus and Remus. Similar to legendary Romulus and Remus, whose caregiver was a wolf, the real children’s caregivers had an animal-like communication system with many words, but no recursion. Their parents could not have taught them spatial prepositions or recursion; children had to invent recursive elements of language themselves. Such an invention of a new recursive language has been observed in contemporary children, for example among deaf children in Nicaragua.

“The acquisition of PFS and recursive language 70,000 years ago resulted in what was in essence a behaviorally new species: the first behaviorally modern Homo sapiens,” concludes Dr. Vyshedskiy. “This newly acquired power for fast juxtaposition of mental objects in the process of PFS dramatically facilitated mental prototyping and led to fast acceleration of technological progress. Armed with the unprecedented ability to mentally simulate any plan and equally unprecedented ability to communicate it to their companions, humans were poised to quickly become the dominant species.”

Humans acquired an ability to trap large animals and therefore gained a major nutritional advantage. As the population grew exponentially, humans diffused out of Africa and quickly settled in the most habitable areas of the planet, arriving in Australia around 50,000 years ago. These humans were very much like modern humans since they possessed both components of full language: the culturally transmitted recursive language along with the innate predisposition towards PFS, enabled by the “PFC delay” mutation.

About this neuroscience research article

Source:
Pensoft Publishers
Media Contacts:
Dr Andrey Vyshedskiy – Pensoft Publishers
Image Source:
The image is credited to J Duckeck.

Original Research: Open access
“Language evolution to revolution: the leap from rich-vocabulary non-recursive communication system to recursive language 70,000 years ago was associated with acquisition of a novel component of imagination, called Prefrontal Synthesis, enabled by a mutation that slowed down the prefrontal cortex maturation simultaneously in two or more children – the Romulus and Remus hypothesis”. Vyshedskiy A.
Research Ideas and Outcomes. doi:10.3897/rio.5.e38546

Abstract

Language evolution to revolution: the leap from rich-vocabulary non-recursive communication system to recursive language 70,000 years ago was associated with acquisition of a novel component of imagination, called Prefrontal Synthesis, enabled by a mutation that slowed down the prefrontal cortex maturation simultaneously in two or more children – the Romulus and Remus hypothesis

There is an overwhelming archeological and genetic evidence that modern speech apparatus was acquired by hominins by 600,000 years ago. On the other hand, artifacts signifying modern imagination, such as (1) composite figurative arts, (2) bone needles with an eye, (3) construction of dwellings, and (4) elaborate burials arose not earlier than 70,000 years ago. It remains unclear (1) why there was a long gap between acquisition of modern speech apparatus and modern imagination, (2) what triggered the acquisition of modern imagination 70,000 years ago, and (3) what role language might have played in this process. Our research into evolutionary origin of modern imagination has been driven by the observation of a temporal limit for the development of a particular component of imagination. Modern children not exposed to recursive language in early childhood never acquire the type of active constructive imagination called Prefrontal Synthesis (PFS). Unlike vocabulary and grammar acquisition, which can be learned throughout one’s lifetime, there is a strong critical period for the development of PFS and individuals not exposed to recursive language in early childhood can never acquire PFS as adults. Their language will always lack understanding of spatial prepositions and recursion that depend on the PFS ability. In a similar manner, early hominins would not have been able to learn recursive language as adults and, therefore, would not be able to teach recursive language to their children. Thus, the existence of a strong critical period for PFS acquisition creates an evolutionary barrier for behavioral modernity. An evolutionary mathematical model suggests that a synergistic confluence of three events (1) a genetic mutation that extended the critical period by slowing down the prefrontal cortex development simultaneously in two or more children, (2) invention of recursive elements of language, such as spatial prepositions, by these children and (3) their dialogic communications using these recursive elements, resulted in concurrent conversion of a non-recursive communication system of their parents to recursive language and acquisition of PFS around 70,000 years ago.

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  1. Andrey Vyshedskiy starts from the assumption that our ancestors had fully developed rich-vocabulary articulate language already 600 000 years ago. In his view, linguistic abilities were already well developed in humans as well as neanderthalers, but modern language, characterized by ‘recursivity’ originated only some 70 000 years ago.

    He bases the assumption that our ancestors could speak already 600 000 years ago on 1) changes in the hyoid bone, 2) the flexion of the bones of the skull base, 3) increased voluntary control of the muscles of the diaphragm, 4) the anatomy of external and middle ear and 5) the evolution of the FOXP2 gene (Dediu & Levinson 2013, cited by Vyshedskiy).

    However, I have argued that all of these traits are more parsimoniously explained by the vocal abilities needed for song, as we are clearly a musical primate in the first place. Only later on, the numerous vocal and motoric skills that had been developed for singing (and dancing) were used to develop articulate language (Vaneechoutte 2014).

    First, the specific human skull morphology (arguments 1 and 2) and voluntary breath control (argument 3) are more easily understood by the hypothesis that these traits were developed for singing, as song has evolved several times independently in different lineages of birds and mammals. Moreover, singing does not require the simultaneous development of vocal dexterity and semantic/symbolic capacity, while such an unlikely coincidence is required when assuming that these traits were newly developed for articulate/symbolic language itself.

    Next, with regard to the anatomy of the external and middle ear, Vyshedskiy correctly points out that “modern humans show increased sensitivity to sounds between 1 kHz and 6 kHz and particularly between 2 kHz and 4 kHz. Chimpanzees, on the other hand, are not particularly sensitive to sounds in this range (Martínez et al. 2004, Martínez et al. 2008)” and he considers this as one of the arguments for the presence of language already 600 000 years ago. However, again, this specific auditory sensitivity is better explained by our musical abilities than by putative speech abilities, as I have argued (Vaneechoutte 2014): “Another unique characteristic of humans that can be read from fossils, …, is not related to the production of vocal signals but to their reception. Apparently, we are endowed with a heightened sensitivity to the midrange frequencies’ tones, i.e., 2-4 KHz (Martínez et al., 2009) or 2-5 KHz (Despopoulos & Silbernagl, 2003), compared to other primates. Martínez et al. (2009) conclude, through the study of the skeletal anatomy of the middle and outer ear of middle Pleistocene hominids, from the site of the Sima de los Huesos (Spain) and from Neanderthals, that this ability was already present at least 500,000 years ago. Because this frequency is typical of human speech, they conclude that these data provide important clues to the origin and evolution of spoken language. However, this is also the frequency range of the singing voice. Intriguingly, from their data, it appears that the highest sensitivity is situated around 3000 Hz, known as the ‘singers’ formant, present in the spectra of trained (especially male) singers, but absent in speech. It is this increase in energy at 3000 Hz which allows singers to be heard and understood over an orchestra (http://en.wikipedia.org/wiki/ Music_theory).”

    Finally, also the interpretation of FoxP2 as an unambiguous indication for language ability is very biased, as I have argued (Vaneechoutte 2014): “More importantly, animal studies indicate a much broader function and more conserved roles of this gene in patterning and plasticity of neural circuits, including those involved in integrating incoming sensory information and outgoing motor behaviors. It has been linked to motor skills in mice and to vocal production learning in songbirds (Fisher & Ridley, 2013), and the rapid evolution of this gene has been observed in bats as well (Jones et al., 2013). Since language is about vocal dexterity (i.e., motoric activity), it can be expected that mutations in this gene will have consequences for language, but these consequences are pleiomorphic and will include deficits other than specifically linguistic ones. Fisher & Ridley (2013) conclude, as we did before (Vaneechoutte & Skoyles, 1998), that it is unlikely that FOXP2 triggered the appearance of spoken language in a nonspeaking ancestor. Also, because singing and dancing may be influenced by this kind of gene, it can be concluded that this gene is linked with vocal dexterity in general, but not specifically with language.”

    The scenario whereby humans developed singing abilities is rather straightforward, as song has been evolved numerous times independently by different lineages of birds and mammals. Moreover, song (and dance) played and still play a pivotal role in the social life of human beings.
    Vyshedskiy points to the presence of articulate language as a pre-adaptation to recursive articulate language: “In some sense, the near-modern speech apparatus circa 600,000 years ago can be viewed as a pre-adaptation for recursive language“. In fact, a much more probable evolutionary scenario, which also enables to explain for example the many differences between languages, is provided by considering instead the presence of singing abilities as a pre-adaptation to language.

    Besides the fact that the claim that evidence points to articulate language in our ancestors already 600 000 years ago is very one-sided, also the Chomskyan claim – taken for granted by Vyshedskiy – that recursive ability is specific for language is not very strong, because recursivity is already apparent in song, as reviewed and further substantiated by e.g. Koelsch et al. (2013). As such, our singing abilities not only explain our vocal dexterity but our ability for recursivity as well.

    Finally, even the recency of the origin of ‘modern’ human characteristics, i.e., only 65-40 000 years ago, is apparently debatable, as there are indications that such characteristics are already apparent in the fossil record since 200 000 years, as such largely coincident with the origin of Homo sapiens (Mcbrearty & Brooks 2000).

    Besides the criticisms on the validity of the claims put forward by Vyshedskiy, the Romulus and Remus hypothesis itself suffers from limited plausibility, as it is in need of the co-occurrence of several already unlikely events all at about the same time. Indeed, he points out himself that his hypothesis is rather problematic for several reasons, e.g.:
    “Two observations have a profound consequence on phylogenetic acquisition of recursive
    language: 1. dialogs with non-recursive homesign systems do not suffice for the acquisition of
    PFS and 2. dialogs with the use to a recursive language have to occur during the period of
    highest neural plasticity, which peaks before the age of two, diminishes greatly after
    the age of five, and expires completely some time before puberty.
    Simply put, it is not enough to be fully genetically modern individual to acquire PFS, one
    needs to be exposed to recursive language early in childhood. This results in the proverbial
    ‘chicken and the egg’ problem since neither PFS nor recursive language could be acquired
    phylogenetically one before the other. This dependency creates an evolutionary barrier,
    which can be cleared only if multiple factors fall in place within a single generation. The
    following chapters put forward a hypothesis that resolves this conundrum by proposing that
    these two processes – the neurologically-based PFS and the culturally-transmitted
    recursive language – were acquired phylogenetically at the same time.”

    To resolve this evolutionary conundrum, he suggests something like the co-occurrence of three or more miracles as a solution:
    “An evolutionary mathematical model suggests that a synergistic confluence of three events (1) a genetic mutation that extended the critical period by slowing down the prefrontal cortex development simultaneously in two or more children, (2) invention of recursive elements of language, such as spatial prepositions, by these children and (3) their dialogic communications using these recursive elements, resulted in concurrent conversion of a non-recursive communication system.”

    Vyshedskiy hypothesizes, on the basis of several one-sided interpretations of fossil and genetic data, that our ancestors could speak already 600 000 years ago. Furthermore, he hypotesizes that we had to await until 70 000 years ago for the co-occurrence of several unlikely events to develop recursive thinking, finally leading to modern language. In summary, the presence of rich vocabulary language already before the presence of Homo sapiens, the claim that the clue to modern language is recursivity and that recursivity was a recent development, are all very debatable, although some of these hypotheses are considered as established knowledge. Moreover, the scenario proposed by Vyshedskiy requires several unlikely events to occur simultaneously, rendering the already enigmatic origin of articulate language even more improbable.

    Instead, we propose that our ancestors were singing (and dancing) since at least one million year ago, as such predisposing us with the vocal dexterity (and recursive abilities, although the latter are not generally used in many spoken languages), needed for the development of articulate language, which developed between 300 000 and 40 000 years ago.
    The spark that finally lead to the development of articulate language remains unclear, but may have been cultural rather than genetic (Vaneechoutte & Skoyles 1998).

    The hypothesis that our vocal dexterity results from our singing abilities and as such functioned as an exaptation (pre-adaptation) that rendered the origin of articulate language less improbable, provides us with a much more parsimonious pathway than the one provided by Vyshedskiy to explain the most enigmatic characteristic ever evolved in the animal kingdom: articulate/symbolic speech.

    Mario Vaneechoutte

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    Vyshedskiy A. Language evolution to revolution: the leap from rich-vocabulary non-recursive communication system to recursive language 70,000 years ago was associated with acquisition of a novel component of imagination, called Prefrontal Synthesis, enabled by a mutation that slowed down the prefrontal cortex maturation simultaneously in two or more children – the Romulus and Remus hypothesis. Research Ideas and Outcomes 5: e38546. doi: 10.3897/rio.5.e38546.

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