The one about Origin of Language and its Neural Pathways
All living beings communicate. But, language is unique to humans. Language allows us to discuss ideas that don’t physically exist. Animals can communicate a warning for danger when they see a lion approaching. But an animal cannot tell its group that it saw a lion eating a bison earlier and that they should go check the area later for leftovers. Even our closest relatives, chimpanzees can be taught few basic sign language (such as “I want a banana”), but no amount of effort would enable us to teach them our language. Many scientists believe language and cognition arose together. Cognition is defined as “the mental action or process of acquiring knowledge and understanding through thought, experience, and the senses.” Could we think without language? Did language enable us to think or did emergence of cognition in our minds give rise to language? How did we learn enough language ourselves to even ask this question?
In this blog, I aim to explain how a language so unique in animal kingdom came to be. I will go over genetic and evolutionary theories for origin of langauge. I also explain how speech is produced using various parts of our body including lungs, mouth and throat. Eventually my goal is to explain how our brain is organized to comprehend and produce language. There are two main areas dedicated to understanding and speaking language in our brain called Wernicke’s area and Broca’s area respectively. These two areas along with many others interconnect to create the magic of language.
PART I: The Language
Theories of Origin of Language
So, primates didn’t have language, but, how about our even closer relatives, the Homo genus? We have enough evidence to believe that species like Neanderthals must have had some primitive form of language. They discovered and tamed fire and used it for cooking. They buried their dead and took care of the elderly. They made art. Why do I assume their language was primitive? Well, it may not have been, but us Homo sapiens did somehow manage to drive every single Homo genus that existed alongside to extinction. At least 6 other human species existed with us around 70,000 years ago. By 12,000 years ago we were the only species standing. What’s noteworthy is that us humans came in picture about 200,000 years ago and for 130,000 years we didn’t really do much. And then something happened around 70,000 years ago that gave us a huge survival edge. In comparison, the longest surviving human species, Homo erectus lived for more than 2 million years. A leading theory is that this survival edge was language. Sure, Neanderthals could cook and paint, but maybe their primitive language didn’t allow for strategic planning, learning new skills, and making better weapons. How else could we have defeated a species that not only was physically stronger, but also better adapted for the cold weather they lived in. How are we here today sending robots to other planets when all other human species have gone extinct? But where did this language that is so unique in the entire animal kingdom, arise from?
There are many theories for origin of language which have given rise to many debates over the years. Unlike written language, spoken language does not leave any direct evidence behind. In fact in 1866, the Linguistics Society of Paris refused to accept any more papers on this topic after declaring it irresolvable.
Charles Darwin argued that people developed oral language by using their mouths to imitate the gestures of an existing sign language. This preexisting sign language could have evolved as a result of an upright posture which freed up our hands for gestures. Then oral language evolved to free our hands for other things. From a grammatical standpoint, sign language is just as sophisticated as spoken language and triggers the same brain areas.
According to another set of theories, language emerged from the complexity of the social world in which primates lived. Language is a social or a group trait rather than an individual one. British anthropologist Robin Dunbar’s “gossip” theory is one of these theories based on social complexity. This theory suggests that language evolved as a means of sharing information about the world. But the most important information that needed to be conveyed was about humans, not about lions and bisons. Our language evolved as a way of gossiping. According to this theory Homo sapiens is primarily a social animal. Social cooperation is our key to survival and reproduction. The gossip theory may seem like a joke but numerous studies support it. Even today the vast majority of human communication — whether in form of emails, phone calls or newspaper columns — is gossip. It comes so naturally to us that it seems as if our language evolved for this very purpose. In primates, it is mutual grooming that serves this social function.
Humans are also political animals. As more complex groups and social hierarchies formed, language could have arisen from the need to choose allies or formulate laws.
Another group of theories collectively known as the vocal theories, state that about 100,000 years ago some changes in our mouth (lips, tongue, cheek, jaws, roof of our mouth) and pharynx (passageway between throat, mouth, and nose) gave us control over our vocal cords. Now, we could create our own sounds instead of the usual instinctive cries. To understand the significance of these changes in mouth and pharynx we first need to understand how sound is produced with our larynx (voice box).
SOUND PRODUCTION
Our vocal apparatus is like two different musical instruments at once: a wind instrument (lungs) which is the source of air and a string instrument (vocal cords) which provides a vibrating component.
When we speak, we inhale and exhale air through our mouth. Our inhalations become faster and shorter and our exhalations increase the pressure and volume of airstream which vibrates the vocal cords in the larynx. The larynx is a cylindrical chamber containing a small opening called glottis which is surrounded by the highly elastic ligaments of vocal cords. These cords are a matched pair of muscles and ligaments, pearly white in colour, 20 to 25 millimetres long, and coated with mucus. Air passing through the glottis vibrates the vocal cords and produces sound waves. The cords are attached to two cartilages in the front (Adam’s apple) and the back. By moving these cartilages, we moved the cords up or down. The pitch of the sound produced depends on the diameter, length, and tension in the cords.
The entire larynx is involved in sound production because its walls vibrate, creating a composite sound. When you speak a sentence, you modify the vibration frequency of your vocal cords many times to produce the acoustic vibrations (sounds) that are the raw materials for the words themselves.
EVOLUTION OF LARYNX
Scientists long believed that primates couldn’t produce all intricate sounds like us because of an anatomical difference. In both primates and babies the larynx is located much higher. While this gives them the advantage of being able to breathe while eating, they are incapable of intricate speech. As primates evolved to become upright, the neck pushed outwards and the base of the skull pushed the larynx further down. A lower larynx meant pathways for stomach and lungs would intersect increasing risk for choking. It therefore seems that the advantage that this descended larynx provides is a vocal communication system that makes this risk of choking worthwhile. This theory could explain why chimpanzees can be taught to sign “I want a banana” but can’t be taught to actually say those words. But what about a parrot that could mimic our speech incredibly? Is that parrot capable of language? No. It can only mimic our sounds but has no comprehension. So, it seems like a great and fitting theory, but it can’t be the full story. Other animals like deers have a lower larynx as well. In primates, earliest evidence of this descent of larynx seems to have occurred in Homo ergaster who existed almost 2 million years ago. And as early as 600,000 years ago the larynx was in its current position in Homo heidelbergensis. (Read my human evolution blog to learn more about these people). These findings lead to the conclusion that a vocal apparatus capable of articulate language probably existed nearly half a million years before people began to speak.
Here’s where our mouth and pharynx come into play. While the larynx produces the vibrations without which you would have no voice, it’s other parts of your vocal apparatus that make speech possible. For the sounds to be transformed into words, they must then be shaped by the rest of the vocal apparatus. Amplification and echoing of the sound occurs within the pharynx, which is a common passageway that connects the throat (laryngopharynx) to mouth (oropharynx) and nose (nasopharynx). The final production of distinct sounds depends of voluntary movements of the tongue, lips, cheeks, and jaws. For example, some of the easiest sounds to produce are vowels (a, e, i, o, u) which require a relatively open configuration of mouth and vocal cords. That’s why it takes much longer for babies to learn sounds that require more complicated movements of mouth like q, w, f, and other consonants. Did the other human species have this intricate control over their mouth and pharynx? Since this is not something that can be answered by fossils, we can never know for sure. But just like Neanderthals these humans must have had some primitive form of language as they built shelters which would have required cooperation. It’s also true that there is nothing in the Neanderthals’ anatomy that would have prevented them from using articulate language. But the fact remains that 70,000 years ago every one of these species started going extinct thanks to us. What gave us such significant advantage? What makes a parrot’s speech different from ours? We believe it’s cognition and our ability to think.
Genetics of Language
We can follow the evolution of eyes from fish to humans and form a step by step method of how that could have happened. There’s a clear picture of progression from a fish’s eye to a human’s eye. But the same can’t be done for language because language leaves no direct evidence behind. But the story of us Homo sapiens suddenly taking over the world 70,000 years ago suggests that genetic mutation could have provided us with that significant advantage. This genetic theory of language is known as Chomskyian theories, after Naom Chomsky. This theory suggests that an unlikely genetic mutation occurred in our species about 100,000 years ago and rewired our brain for langauge. This reorganization of brain gave rise to the instinct of language and caused an explosive growth in cognition. According to this view, language is innate to us humans — it’s in our genes. And that is supported by the fact that despite thousands of different languages that exists, grammar is universal. Grammatical structures in all languages including sign language have similar pattern. It’s extremely hard if not impossible to create a language with no grammar. It’s also supported by how fast children learn language. Language and all its grammatical rules are complicated. There could be an infinite number of sentences formed from the words of a language. Children master this complex operation of language so easily that they must have some innate knowledge of these principles. Even before the age of 5, a child can produce and understand sentences that they have never encountered before. This universal grammar is embedded in our neuronal circuitry. This view of origin of language can be somewhat anti-evolutionist. Because from this viewpoint, Homo sapiens are not just an improved version of their predecessors (how evolution will have it), but a completely new concept. But then the questions also arises, if language is innately human, would a child brought up by animals be capable of complex thought compared to its animal relatives?
KE FAMILY and FOXP2 gene
Study of the British family known as the KE family gave the first direct evidence of a genetic relation with language. Out of the 37 members in the family spread across 4 generations, 15 of them had language disorders. Studying the family tree, scientists attributed the disorder to a single gene transmitted by either parents. This gene found on chromosome 7 was called FOXP2. Identification of this gene established the first connection between heredity and human language.
Each of us inherits two copies of the FOXP2 gene: one from our mother, and one from our father, located on each of the two chromosomes in pair 7. Both copies, it appears, must be intact for our language functions to be normal. A person with two defective copies of this gene will suffer from Specific Language Impairements (SLI).
Now the entirety of language being as complex as it is cannot be attributed to one specific gene. But FOXP2 is an extremely important player. If you think of all the genes that contribute to language as forming a tree, then you can think of the FOXP2 gene as the trunk of that tree.
So, despite the many theories of origin of language, the genetic theory is the most widely accepted. But its still important to understand that language is too complex to be located on one gene only. Genes are nothing but codes to make proteins. FOXP2 gene is translated into a transcription factor, which is a kind of regulatory protein. That means it doesn't have one specific job but helps regulate transcription of other genes and proteins. This itself is a big hint that many more genes are involved in creating the complete art of language.
PART II: The Brain
PAUL BROCA
Our story for identifying parts of brain associated with language begins with French neurosurgeon, Paul broca and his patient, ‘Tan’.
In April of 1861, a 51 yo patient at a hospital in France was assigned to surgeon named Paul Broca. Patient, Louis Victor Leborgne, was suffering from a gangrenous leg infection. Broca became more interested in a specific language disorder the patient had which made him unable to speak fluently. In his 40s, Leborgne had become hemiplegic and bedridden. His speech difficulties started around this time. Leborgne was still aware of his surroundings and appeared to have thoughts he wanted to communicate. But whenever he tried to do so, he was unable to get the words out. In fact, the only word he could say was “tan”, which later earned him the nickname of Tan. Even when he tried to write down his thoughts, his hands would be unable to write the words. He could otherwise sing and use his hands for other things. This was so odd!
Leborgne died soon after and Broca performed an autopsy on his brain. He was curious to see what type of brain anomaly would produce this strange speech deficit. The damage found in Leborgne’s brain was later found in other patients with similar speech production disorders. This is now known as Broca’s area. Language disorders resulting from damage to this area is known as Broca’s aphasia. Broca’s area is close the motor cortex containing nerves for face and mouth. Though it’s close to the mouth area, Broca’s area sends signals to hands as well. It’s involved in production of sign language as well as our body language. Damage to this area as we just learnt impairs speech production while keeping speech comprehension intact.
CARL WERNICKE
In 1874, German psychiatrist, Carl Wernicke identified another part of brain dedicated to comprehending language. In contrast to patient Tan, his patients could speak fluently in seemingly perfect grammar but make zero sense. These patients would string together syllables and sounds to produce a speech that seemed like a fluent foreign language but was in fact meaningless. These patients were also incapable of understanding language. Patients with Broca’s aphasia know what they want to say but are incapable of doing so using spoken, written, or sign language. Patients with Wernicke’s aphasia could speak and write and sign with no difficulty but nothing they wrote or spoke or signed would ever make any sense. Wernicke’s area is next to the auditory cortex.
LANGUAGE IS A LEFT HEMISPHERE TASK
Both Broca’s and Wernicke’s area are located in left hemisphere giving rise to the theory that language is primarily a left hemisphere task. And this is mostly true. About 90% of people are right handed and 95% of them have these areas in their left hemisphere. In comparison, 70% of left handed people have the language areas in left hemisphere. So, there is a small but significant enough proportion of people who for whatever reason have their language areas on right hemisphere. But the point remains that no one has two Broca’s area — one for each hemisphere. This is unlike our motor cortex that the Broca’s area sits next to. We have motor cortex on both hemispheres — given left hemisphere contains nerves from right side of the body and vice versa. Cortex is the top layer of brain where all higher order processing happens. Read my blog on Brain to learn more about this.
But even with Broca’s and Wernicke’s area being in left hemisphere, the right hemisphere has a fair contribution in processing langauge. Right hemisphere gives us the ability to go beyond the literal meaning of words. It’s the hemisphere involved in getting sarcasm, irony, metaphors, and punch line for jokes. It also helps in understanding non-verbal cues as well as in recognizing faces. Wada’s test can be performed to identify which hemisphere contains the Broca’s and Wernicke’s area in a particular patient.
Geschwind-Wernicke model
In 1960s, American neurologist, Norman Geshwind presented a new more interconnected pathway of language in our Brain. According to Geshwind, there are pathways connecting the Wernicke’s Area to Broca’s Area called the Arcuate Fasciculus. Wernicke’s area is heavily connected to the auditory cortex while the Broca’s area is connected to the motor cortex. Because language also involves reading we have to connect the language areas to the visual cortex. These is done via the Angular gyrus which sends information of what we are reading to the Wernicke’s Area which sends to to Broca’s via the arcuate fasciculus. Broca’s area finally sends information to our mouth for speech production, our face for expressions, and our hands for body language. In contrast, when we hear something information comes from our ears to the auditory cortex (learn more about this pathway in my Decoding Sound blog) and then onto the Wernicke’s area and rest is the same. Though this is a great way of understanding language processing in the brain the Geshwind-Wernicke’s model has its shortcomings. It falsely assumes that these various areas of language are connected in a series of steps where one step needs to precede the next. But we know now that’s not always true. For example Broca can send signal to the motor cortex, however meaningless, even if all pathway leading to it are broken.
Marsel Mesulam
In the 80s, American neurologist Marsel Mesulam proposed a different model for understanding brain’s language circuitry. Mesulam’s model posits a hierarchy of networks in which information is processed by levels of complexity. According to this model, tasks of differing complexity such as reciting the alphabet or having a deep and meaningful conversation would utilize different brain areas. Mesulam still believed in two epicenters for language processing — Broca’s and Wernicke’s. But he understood semantic processing to be much more complicated than the step by step hirarchy of Geschwind-Wernicke model. In this model, our limbic system which controls emotions and stores memories is involved in language processing as well. Both Broca’s and Wernicke’s areas are further subdivided with each area dedicated for a different task. For example, Broca’s area is actually now definied as comprising Broadman’s area 44 and 45. Broadman areas were originally defined and numbered by German anatomist Korbinian Broadman based on cellular organization of neurons in cortex. He believed these organizations to be based on functions which later turned out to be true.
So, Broca’s area 44 which is closer to the motor cortex is involved in phonological processing and language production. Broca area 45 on the other hand is indirectly involved in accessing meaning. Wernicke’s area, like Broca’s is also subdivided in 3 separate areas with unique functions. The first responds to spoken words (including the individual’s own) and other sounds. The second responds only to words spoken by someone else but is also activated when the individual recalls a list of words. The third sub-area seems more closely associated with producing speech than with perceiving it. There’s yet another area involved in language processing called the supramarginal gyrus which is connected to the angular gyrus which connects visual cortex to language processing areas. While the angular gyrus processing meanings of words being read, the supramarginal gyrus phonological and articulatory processing of words.
So, yes there are some clear pathways of language in our brain but it’s way more complex than we can imagine. Functional MRI (fMRI) of brains which light up areas being used during a specific task have shown majority of the brain is responsible for creating the complete language. Yes, some areas like Broca’s and Wernicke’s have a clear connection but there are definitely not the entire story. For example, even a specific task like storing meanings of words is done by brain in a complex manner. For example, if the temporal pole (the anterior end of the temporal lobe) is damaged, the category “famous people” is lost; if a lesion occurs in the intermediate and inferior parts of the temporal lobe, the category “animals” disappears.
Language Disorders
Language disorders are called Aphasia. We aready learnt about Broca’s and Wernicke’s Aphasia. Here are a few more interesting ones:
AGRAPHIA: inability to write
ALEXIA: inability to read
ANOMIA: inability to name thing
ACALCULIA: inability to calculate
GLOBAL APHASIA: most severe kind; cannot speak or understand
