Early humans developed the anatomy for producing speech hundreds of thousands of years ago. There is evidence that perhaps even Homo erectus could manage complex vocalisation, based on observed anatomy from the fossil records. What makes modern humans unique is that we can skilfully link conceptual objects, in space and time, through recursive language.
Scientists have long understood that the Wernicke’s and Broca’s areas of the brain are linked with language production, but for the full recursive language that we modern humans utilise today, there is considerable involvement of regions in the lateral prefrontal cortex (LPFC). Modern humans include a neurological architecture that was not available to early hominins. Indeed it was probably not part of the make-up of our archaic Homo sapiens ancestors living 100,000 years ago.
It is a function of the LPFC to process objects from memory into a helpful mental image arising from a sentence, being an aspect of human imagination. To be clear, the word imagination here is different to how we might use it as a descriptor for dream imagery. Most would also consider dreaming imaginative but this does not involve the LPFC. In fact, the region of the brain which processes language into images does not function while we are asleep and when it is damaged individuals will not experience any impact on dreaming. Imagination as it relates to communication and the LPFC is given the name Prefrontal Synthesis.
Damage to the critical LPFC region of the brain will lead to varying degrees of a condition called frontal dynamic aphasia which becomes apparent only when the individual needs to imagine several objects or persons in combination during a conversation. Objects mentioned which requiring temporal or spatial relations will elicit particular confusion, such as ‘the plane is flying through the clouds’ or ‘new year is before Christmas’. Our ability to comprehend these relationships is something we take for granted but pause for a moment and imagine you could not establish such relationships for any conceptual objects. Essentially it is the undoing of our ability to process and synthesise unusual mental images constructed from multiple objects stored in our memories.
Prehistoric human communities’ individuals with what we would now consider a PFS disability, having yet acquired this adaptation phylogenetically, could still communicate but only using a non-recursive system. While we can’t know to what level of complexity their vocabulary had arisen, we can be sure that they would not understand recursive language meaning no use of spatial prepositions. They wouldn’t be able to tackle instructions with temporal and spatial elements like ‘catch that monkey on the rock so we can eat it for dinner tonight’.
The primitive communication system would have been extremely limiting without spatial prepositions or the ability to describe objects in combination. Humans in that situation could have vocalisations for simple concepts such a ‘dangerous animal’ or ‘I’m hungry’, but it would be little more than we see in the rest of the animal kingdom (and perhaps more straightforward than dolphin communication). Linguistics today has no term for a language of words without recursion, meaning that to call it ‘language’ provokes confusion. Instead, the researchers refer to this as a ‘rich-vocabulary non-recursive communication system’.
Mysteriously there is more to the story than a need for LPFC development in the acquisition of recursive language. A child must be exposed to such a communication system during their formative developmental years. In cases where a child has been deprived of language instruction until puberty, perhaps through being a victim to extreme neglect, they will exhibit PFS disability for life. It may not be surprising to know that PFS disability is also common among congenitally deaf or autistic people who did not have any concerted efforts of language development intervention during early life.
PFS is unlike the processing of visual phenomena or auditory signals which happen even if a child lives alone and isolated in the forest. The neurological networks required for PFS will only develop correctly if a child lives with a community of humans who are themselves using a recursive language system and are actively focused on communicating with the child in this format. It is considered essential that instructive dialogue occurs during neural plasticity is highest, which peaks by the age of two, falls sharply around five, and ends entirely ahead of puberty.
This interdependency between brain architecture and a system which both engineers and require this neural structure creates an evolutionary barrier. It is understood that in pre-modern humans (including Neanderthals) the critical period ended by around two years of age, making the acquisition of PFS impossible.
For our own ancestors to have acquired PFS necessitated a genetic mutation which delayed the maturation and lengthened the critical period with highest neural plasticity. However, the delay mutation found in modern humans is considered deleterious, that is it is treated as a problem code to be removed by evolution. For the genetic information needed to allow PFS to remain required a quick leap to recursive language and the benefits, it would bring. Yet, as aforementioned both the language system itself and the brain structures must emerge in the same single generation and must do so in multiple children. All of this makes for a highly unlikely scenario, and yet here we are speaking to each other and able to link various conceptual objects.
The Cultural Missing Link
Many artefacts which point to the use of human imagination, such as composite art pieces, ritual burials and bone needles seem to emerge only after 70,000 years ago. This is widely understood to mark the beginning of the human Neolithic cultural revolution. It is soon after this period that modern humans expanded rapidly across Eurasia and into the Americas.
The same genetic mutation that slowed down the development of the prefrontal cortex allowing for the potential to develop recursive language may have also impacted the capacity for abstract thinking which prompted this explosion in new ideas 70,000 years ago. Recursive language likely plays quite a role in the revolution as it allowed people to explain how to perform complex tasks, things previously impossible to communicate – perhaps even to conceptualise.
Dr. Vyshedskiy, the neuroscientist behind the new study, has devised a possible solution to the evolutionary paradox of recursive language development. The original hypothesis, named for the legendary Roman twins Romulus and Remus as it requires minimum two or children to acquire the mutation for an extended critical period. These special children must be in the same group and would have to spend a lot of time talking to each other.
These children (whether two or more) would need to invent and share recursive elements of language, such as spatial prepositions, while still in the crucial period (assumedly before 5 years old). This could possibly then allow acquisition of recursive-conversations-dependent PFS. As adults, the individuals would then need to teach recursive language to their own children, assuming the deleterious mutation was passed on to the next generation. Transmission across generations would be more likely if it were a male and female with the same mutation, and they happened to produce children together.
“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.”
It is easy to see how this new ability would have super-charged humanity allowing new forms of hunting with engineered traps or planning and scheduling an ambush. As modern humans became more successful, their numbers grew, and this prompted new migrations, likely involving improved watercraft (real wooden boats). Modern human populations would have begun to range much further and eventually inhabiting all of Eurasia and even America.
We can’t leave this topic without raising one intriguing point. Across the world indigenous people tell us legends of the gods that taught humanity language. Could it be the case that some visitor to our world modified the genes of our ancestors and then gifted the children with a recursive language? It’s certainly a simple solution for the evolutionary paradox and requires none of the mathematically unlikely scenarios involved in the Romulus and Remus hypothesis.