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The Co-evolution of Manual Dexterity and Language Grammar

Posted By Robert DePaolo On August 23, 2012 @ 9:13 pm In Psychology | No Comments

By Robert DePaolo

Abstract

This article discusses the advent of human language grammar as a concomitant of the fine motor planning and executive skills that also facilitated advanced tool making. Neither skill is viewed as antecedent. Instead the point is made that they were essentially concurrent and interdependent in human evolution; that the brain’s capacity to orchestrate manual behaviors toward a pre-planned outcome as seen in tool making extended to oral-motor cortical regions (and vice versa), enabling early humans to develop simultaneously a manual and linguistic grammar.

The idea that human language derives from tool making has been supported by a number of researchers and theoreticians, for example Sample (2010) and Stout (2011).That is in part due to the anatomical, functional and neurological interrelationship between oral and fine motor expression.
Around 75,000 years ago the human brain reached its current volume of roughly 1200 centimeters. Its expansion featured an outward growth of the outer layer – known as the cerebral cortex. Not only did this brain section expand substantially, it also folded up in development so as to maximize its size and experiential influence without overriding the size of the human skull case. The cause of cortical expansion – to the extent that one can insert determinism into the evolutionary process – is uncertain.

There are several possibilities. One is that the primate brain has always had a higher probability of encephalization due to its need to adapt to the sensory-motor demands of an arboreal existence. Implicit in this idea is that Darwin’s concept of chance mutations is inaccurate; that the genetic history of any given organism skews its mutative drift. At the risk of invoking the Aristotelian notion of inside-out teleological development, it would seem lions are more likely to develop changes in coat color and canines than to develop gill slits. Thus “predisposition theory” (which holds that mutations are skewed in terms of a prior ontogenetic template) might provide one answer.

Another factor might have been greater exposure to sunlight. Since the upright posture hides much of the body’s mass from sun exposure bipeds were able to travel long distances without suffering heat exhaustion as readily as their quadruped cousins. On the other hand, while the body proper would have insulated from solar exposure, that would not have been true with regard to the head, brain and sensory organs. Exposure to those anatomical sites would have been intense and might have triggered hormonal changes and adaptations which in turn led to more rapid mutations, including neotenous development (the tendency for maturation to extend beyond the usual timetables and to a prolonged period of brain growth and development).

Another, less deterministically toned possibility is that brain expansion might have simply fed on itself. More specifically, as the hominid brain expanded, the brain’s noise level (and need to seek information to resolve that noise) through information gathering would have increased. That might have embellished the curiosity drive, leading to prolific migrations and exploratory behaviors, thereby increasing exposure to more varied environments and sunlight, and requiring adaptations to vagarious circumstances, such as climate, predation, food finding, hunting etc. This view, which could be called Impetus theory, holds that brain expansion is ultimately the result of prior brain expansion.

Irrespective of specific or multiple causations, the human cerebral cortex appears to have evolved in sync with morphological changes in late hominids (the upright walkers who preceded the human line).

Many Species – Two Body Types…

The fossil record implies that two separate hominid lines branched off from the first upright walking primate, Australopithecus afarensis. While a number of hominid species overlapped with and succeeded this group, a dichotomy in body structure seems to have been somewhat typical. Some groups evolved a robust look while others took on a more gracile (slender) physique. The dichotomy appears to have begun with the robust and gracile Australopithecus groups (Crain 2011) and continued up to the time of Neanderthal and Cromagnon.
The advantages of both body types are obvious in the short term but their long term evolutionary benefits are less clear. The more robust species were obviously stronger, which probably aided them in self defense. On the other hand they likely moved slower and were primarily herbivorous. (Here one can draw a rough parallel between modern chimps and gorillas). That would have conceivably put up a barrier to cognitive evolution in part because unlike prey animals plants are easy to find, stay put and do not ordinarily offer much resistance.

On the other hand hunting is a superb cognition-builder, since it entails social cooperation, sensory acuity, visuo-spatial calculations in the chase and a number of other planning and anticipatory skills. It also requires not just internal body regulation with regard to stealth, energy apportionment, perceptual tracking, shifts in speed and direction. It also demands some anticipatory knowledge of the habits and body language of prey. As paradoxical as it might seem, a good hunter must have an empathic connection to its prey, and a capacity to dual process himself and the creature it is chasing down.

Consequently one might presume that since a hunter’s internal and external feedback capacities are heightened a meat eating hominid is more likely to evolve a greater sense of self, and that if its brain were to expand beyond a certain threshold that might provide an evolutionary ratchet toward both tool making, social awareness and verbal expression. That would supply a cognitive template for language and tool making. The motor aspect is another question entirely.

The Evolution of Motor Finesse…

Aside from speed and agility on the hunt a gracile physique provides other advantages. With less body mass, gracile hominids did not have to devote as much neural control to motor and vestibular functions. As a result the brain could sequester more of the body’s energy reserves. In not having to devote as much time to feeding the meat eater’s cognition could be converted to broader concerns. At the same time having less body mass would have produced an evolutionary trend toward smaller, more facile muscle responses.

As muscles are reduced in mass the appendages they regulate become capable of finer movement patterns. The neuro-motor mechanics of the digits and vocal cords become less cumbersome. Finer distinctions in movement and sound making, modulated by a concomitant shift in the ratio of excitatory/inhibitory influences in the brain become possible.

The human brain is comprised of those two types of neuronal activity. Some fibers excite and facilitate actions while others inhibit actions. The modern human cerebral cortex has more excitatory than inhibitory neurons but the resilience and influence of inhibitory cells is greater (Oku & Lampl 2009) so that there is an overall functional balance. In effect inhibition and excitation come close to canceling each other out in their totality. It appears much of what we call intelligence is grounded in a capacity to block inputs and actions so that we can parse relevant vs. irrelevant inputs. In other words, one hallmark of human cognition is an enhanced capacity to differentiate between objects and other phenomena; something psychologists call discrimination learning. This is enhanced by the egalitarian influence of “stop” and “go” cortical brain cells that exists in the human brain.

The Discrimination Paradigm…

The evolutionary fine tuning of body and brain made sensori-motor categorizing more prolific and precise. At some point the gracile hominid groups, whose brains tended to be larger than the robust species and ostensibly moving in the direction of cortical expansion and toward greater inhibitory influence could distinguish more precisely between movements, objects, sights and sounds.

That might have extended into the domain of cognition; perhaps even set the stage for precursors to cultural phenomena such as law, morality and esthetics.

Being able to tell the difference between the right and left hand, between a well-crafted vs. a crudely made tool, between and among vowel and consonant sounds could have extended quite naturally into other binary judgments, including those pertaining to appropriate vs. inappropriate behaviors, beauty and ugliness, between social norms and deviance, between myself and others…or myself vs. the objects/tools with which I am working.

An enhanced differentiating capability made possible by more efficient orchestration of inhibitory/excitatory patterns might have been the pivot point from which human language grammar and tool making emerged.
While various theoreticians have suggested the freeing up of hands set the stage for tool making, there would seem to be a more important and necessary antecedent. Freed up hands in and of themselves do not provide feedback on performance. In order to craft a tool requires some predetermination of what the outcome should be. Without a sensory, cognitive and/or mnemonic template from which to work no task, or for that matter any form of creativity could ever come to fruition. In other words, to make tools requires an internal processing mechanism in the form of imagination that transcends the realm of the outside world.

The question is: how does a hominid begin to develop such a capacity?

Fine Tuning and the Advent of Self Image…

Assuming the sequence of gracile morphology, cortical expansion, inhibitory/excitatory fine tuning of sensation, movement and cognition occurred in the manner discussed above, one byproduct of that discriminatory enhancement would have been between self and other (the latter of which would include other individuals and the larger environment). The distinction between “myself and the outside world” would have increased the hominid’s ability to monitor his own actions, evaluate the efficiency of stone striking skills and modify those actions. In that context, it was arguably a capacity for “theory” rather than freed up hands that led to sophisticated tool making. That could have led quite naturally into language grammar.

A Generic Grammar…

The question of where, when and why human language grammar came to be has been addressed in many quarters, for example by Botha and Knight (2009) and Dunbar (1996). While various explanations have been offered, there is some research that can take us beyond the realm of speculation. Two of the more noteworthy efforts in that regard were by Murray Gell-Mann and Merrit Ruhlen (2003). They discovered that most of the world’s languages adhere to the SOV model. “SOV” refers to the grammatical sequence…subject-object-verb. While modern English entails a different model known as SVO, e.g. …John drank soda… but as world language go it is atypical. It would seem the SOV model, which characterizes the Romance, Indo-European and most other old languages compromises a grammatical prototype which might have existed in some form during the inception of human language.

Brain, Hand and Mouth…

The neurology of speech and fine motor behavior is indicative. Motor control runs along a narrow strip in the parietal lobe of the cortex and the site of manual control is adjacent to that for oral motor expression. While the human brain has superb parsing capabilities the proximity of manual to oral control sites increases the likelihood of behavioral spillover (Graziano, 2006). Neural activity will tend to flow from mouth to hand absent a super-efficient braking mechanism in the brain. (This might be why non-verbal autistic individuals engage in manual gestures, why humans gesture while speaking and why sign language is such a valuable tool for the hearing impaired).

The spillover factor would not necessarily be a one way street. Absent some specific delineation of pathways resulting from a narrowly conditioned response the relationship would more likely be reciprocal, with a reciprocal feed forward – feedback sequence from hand to mouth and mouth to hand.
In that context it is difficult to determine whether language or sophisticated (imagination-driven) tool making came first. If one assumes their origins overlapped in human evolution, then the SOV model becomes especially intriguing. It would seem to contradict the freed-up hands theory because the grammatical structure of human thought would appear to regard the actor first, the object second and the action third.
The SOV model would imply that early human toolmakers might have approached the task in this way…

I am a toolmaker. I have a memory of what strokes I need to make and of my capacity to create well-crafted tools for the betterment of self and tribe.

I must select a suitable object from which to carve out the desired object.

Having done that, I will now engage in the process of striking and sculpting.
Interestingly, given the nature of human learning, the sequence would not end there.

Rather than motor behavior proceeding blindly forward, the sequence would repeat itself. The tool maker would re-consult the self (how am I doing?) the object (how does the stone look?) then the action (That strike was a bit too soft, have to strike harder to sharpen the edge).That brings into discussion the reciprocal role of language in the tool making process.

An Evolutionary Mediator – Attention… Span

Since, with the exception of a few thinkers there is very little synthesis between the field of anthropology and psychology only speculation can be offered on the question of when, how and to what extent homo sapiens was able to increase his task endurance capabilities. It is one thing to have freed up hands, imagination and fine motor prowess, quite another to be able to sustain attention to task (which can entail an uncomfortably long periods of brain stem and cortical arousal) without incurring mental fatigue. Even if early humans circa 75,000 BCE years had the same brain volume an structure as modern man, there still would have been difficulty with task adherence. That is not necessarily an ancient problem.

Modern humans with Attention Deficit Disorder often have difficulty with fine motor tasks and work endurance. Aside from the use of medications there is ample research to indicate that self-talk can be a good mediator between self and task (Villar 2007). The reason why is fairly clear. Engaging more of the brain in an activity enhances memory and blocks out distractions. It also heightens reinforcement sensitivity by increasing sensory, motor and emotional investment in the task…something often referred to as a “neural trap.” In addition, the use of language can make the task appear less lengthy and cumbersome…for example with phrases like…”almost done,” “a few more whacks” etc.

In that sense the capacity of language to enhance attention span suggests language involvement improves motor performance. Whether that was its original evolutionary benefit is open to question. That it improved performance in general seems not to be.

In finalizing discussion on the possible co-evolution of language and fine motor prowess it is not out of the question to assume they comprise a reciprocal, if not singular function. We use a motor grammar in order to build things, produce art and execute various actions. That grammar is more or less the same sequentially as the SOV model that typifies most languages, from self, to target, to performance. We speak in spatial-relational terms because our words tie in to the mechanical/spatial activities carried out with the hands. In that sense language is actually a covert manipulative device using symbols rather than movements to plan, orchestrate, and execute. Thus It is conceivable that theories of language espousing the existence of universal grammar or language instincts are, while logical and interesting, a bit oblique. It could simply be that the structure of human language is a subset of the grammatical structure of planed movements resulting from among other things the proximity of circuits in the brain devoted to oral and motor expression respectively. Ultimately that raises the question of when human language originated. On that matter there is considerable disagreement but with such a strong correlation between the structure and neural topography of fine motor capacities and human language one might assume some prototypical language grammar formats originated with Homo habilis, the first known toolmaker.

References
Botha, R. & C. Knight (eds) (2009) The Cradle of Language. Oxford, Oxford University Press

Crain, T. (2011) Background of Human Origins According to Evolution. Northwest Creations

Dunbar, R (1996) Grooming, Gossip and the Evolution of Language. London,
Faber and Faber

Gell-Mann, M. & Ruhlen, M (2003) The Origin and Evolution of Syntax. NY Academic Press

Graziano, MSA (2006) The Organization of Behavioral Repertoire in Motor Cortex. Annual Review in Neuroscience, 29, 105-134

Groom, C. (2003); Language Origins. Did Language Evolve Like the Vertebrate Eye or was it More Like the Bird Feather? ProQuest. Discovery Articles

Leonard, W. R. (1999) Meat Eating was Essential for Human Evolution. Berkely.edu article retrieved 1/31/12

Okua, M & Lampl, I (2009) Balance of Excitation and Inhibition. Scholarpedia article

Ruhlen, M (994) On the Origin of Language; Studies in Linguistic Taxonomy. Stanford University Press.

Sample, I Article in: The Guardian; News, Science, Anthropology, Nov.3, 2010

Stout, D. (2011) Stone Toolmaking an The Evolution of Human Culture and Cognition, Philosophical Transactions of the Royal Society. Biological Sciences

Villar, O (2007) Cognitive Treatment for Children with Attention Deficit/ Hyperacivity Disorder. Review and New Contribution. Annuary of Clinical and Health Psychology (3) 19-30.


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