April 25, 2025	PSY 340 Brain and Behavior Class 38: Evolution and Physiology of Language

All living creatures communicate in some fashion using sound, sight, motions, touch, odors etc. as means of signalling.

• Cobra snakes expand their hood to scare other creatures
• Wolves howl to call to others in their pack
• Baboons use touch in grooming each other and showing affection
• Cats mark their territories by rubbing against objects to mark them with their scent

The Evolution and Physiology of Language

A.   Compared to all other forms of animal communication, human language is unique because of it productivity, that is, its ability to produce new signals to represent new ideas.

Human language is distinct from all other known animal forms of communication in being compositional. Human language allows speakers to express thoughts in sentences comprising subjects, verbs and objects—such as ‘I kicked the ball’—and recognizing past, present and future tenses. Compositionality gives human language an endless capacity for generating new sentences as speakers combine and recombine sets of words into their subject, verb and object roles. For instance, with just 25 different words for each role, it is already possible to generate over 15,000 distinct sentences. Human language is also referential, meaning speakers use it to exchange specific information with each other about people or objects and their locations or actions. (Pagel, 2017)

Consider how the invention of the Internet has forced us to create a whole new set of symbols and ways of conveying meanings.

 

B.  Nonhuman Precursors to Language

1.  Common chimpanzees can not learn to talk, but can learn some language skills using American Sign Language or other visual systems. Their use of language-related symbols differ from human language in many ways:

a. The chimpanzees seldom used the symbols in new original combinations (they are not productive).
b. The chimpanzees used their symbols almost always to make a request, only rarely to describe.
c. The chimpanzees produced requests far better than they seem to understand anyone else's request.
d. They do show a moderate degree of understanding of what is communicated to them, e.g., "who?" questions answered by names; "what?" questions answered by things; and "where?" questions answered by places.

2. Bonobos (Pan paniscus) , a "cousin" of the common chimpanzee, when given language training uses symbols in several ways that more resemble humans than common chimpanzees:

a.  They understood more information than they produce.
b.  They use symbols to name and describe objects even when they are not requesting them.
c.  They request items that they do not see.
d.  They occasionally use the symbols to describe past events.
e.  They frequently make original, creative requests.

3.  The reason for the better language skills in the bonobos than in chimps is unknown.

4.  Nonprimates: Alex, African gray parrot (1976-2007) 

Trained by Dr. Irene Pepperberg (originally U Arizona, now affiliated with Brandeis U-Harvard-visiting @ MIT Media Lab) from age 1. Alex died unexpectedly Sept 6, 2007 of heart disease.
 
Alex had relatively extensive language ability with specific objects & concepts:

• Alex "could identify fifty different objects and recognize quantities up to six; that he could distinguish seven colors and five shapes, and understand the concepts of "bigger", "smaller", "same", and "different," and that he was learning "over" and "under".
   
  
• Alex had a vocabulary of about 150 words, but was exceptional in that he appeared to have understanding of what he said. For example, when Alex was shown an object and was asked about its shape, color, or material, he could label it correctly. If asked the difference between two objects, he also answered that, but if there was no difference between the objects, he said “none.”" (Wikipedia, retrieved April 21, 2008)
  

Pepperberg offers an evolutionary explanation for intelligence (which, presumably, is the basis of language) by citing the examples of both apes and parrots who live to become 30 to 60 years old in captivity (but parrots average about 24 years in the wild):

"Nick Humphrey suggested these ideas almost 30 years ago:... given a long-lived creature that exists in a complex socio-ecological system, that creature has likely been selected for high-level intelligence and cognition. I think those same evolutionary pressures work on parrots." ("That damned bird," 2003)

C.  How Did Humans Evolve Language?

  1.  Is Language Just a Product of Overall Intelligence or a Specialized Adaptation? Answer: Probably a Specialized Adaptation

a. The relationship between brain and brain-to-body ratio is unclear (see chart  or click here for larger image). Human beings do not have the largest brain-to-body mass ratio: dolphins, elephants, and blue whales do. Yet these animals do no use language in ways that are parallel to human beings.

b. The evolution of language seems to require a brain mechanism called the phonological loop, that is, the ability to hear and remember something (remember that this loop is one of the elements in Baddeley's model of working memory).

Language also seems to depend upon gestures, particularly those gestures involving the face and mouth. When we listen to others in noisy settings, we pay particular attention to the face and mouth of the other speaker in order to understand what they are saying.

c. People with Normal Intelligence but Impaired Language

"KE" Family (an English Caucasian family; for many years was mistakenly described as of Pakistani origin) & "CS" (an unrelated English boy with same language problem)

Presumably because of an altered dominant gene (FOXP2 ["“forkhead box P2”"] segment on chromosome 7), 16 of 30 people of normal intelligence within one family (& "CS") have severe difficulty with pronunciation, and all other aspects of language. Cases such as this suggest that genetic conditions which affect brain development can impair language without impacting other aspects of intelligence. (Itzhaki, 2003; Liegeois et al., 2003; MacAndrew, 2003).

==> Conclusion 1: General intelligence is not itself sufficient for language.

d. People with Intellectual Disability (Low Intelligence) but Relatively Spared Language

Williams syndrome (also known as Williams-Beuren Syndrome) = people with intellectual disability but good language skills. Also musical rhythm ability. Fascination with faces (fusiform gyrus is 2X normal).

    

A rare disorder (~1 in 20,000 births according to Kalat; ~1 in 8000 live births according to Haas & Reiss, 2012) in which individuals with intellectual impairments have relatively skillful use of language, but limited abilities in other regards. This disorder is caused by a deletion of several genes from chromosome 7. 

Pascual-Castroviejo et al. (2004) summarized other characteristic symptoms:

• Distinctive facial appearance ("elfin-like")
• Intellectual disability (IQ < 70)
• Very socially friendly behavior
• Congenital heart problems including supravalvular aortic stenosis & pulmonary stenosis
• ADHD-like behavior

New/Not in book:

Evelina Fedorenko (MGH/Harvard) & Rosemary Varley (UCL, UK; 2016) report that "language and thought are not the same thing" on the basis of multiple neuroimaging studies

• Patients with global aphasia (= have almost no ability to understand or produce language) can still "add/subtract, solve logic problems, thing about other person's thoughts, appreciate music, and successfully navigate their environments" (abstract)
   
  
• Neuroimaging studies show different patterns of engagement of the brain's language areas. Areas that are active when individuals attempt to understand a sentence are not active when individuals perform other "non linguistic tasks such as arithmetic, storing information in working memory, listening to music" et al. (abstract)
   
  
• Fedorenko et al (2016) conclude that "Evidence from brain imaging investigations and studies of patients with severe aphasia show that language processing relies on a set of specialized brain regions, located in the frontal and temporal lobes of the left hemisphere. These regions are not active when we engage in many forms of complex thought, including arithmetic, solving complex problems, listening to music, thinking about other people’s mental states, or navigating in the world. Furthermore, all these nonlinguistic abilities further appear to remain intact following damage to the language system, suggesting that linguistic representations are not critical for much of human thought" (p. 12)

Conclusion 2: Language does not appear to be a by-product of general intelligence or general intellectual activity

2.  Is Language a Specialization of the Brain?

a.  First proposed by MIT linguistics scholar, Noam Chomsky, an alternate view of the evolution of language is that language evolved as an extra brain module, called a language acquisition device (LAD).  This idea is supported by the fact that children learn language with amazing ease and that children learn language despite the fact they do not hear enough examples to learn the grammatical structure of language (this is called the poverty of the stimulus argument).

Chomsky believes that language did not primarily develop as a method of vocal communication, but a means by which to organize our thoughts internally. In so doing, we developed a particularly important new skill: "symbolic thinking". As Ian Tattersall (2024) summarizes

And it is certainly true that no other human attribute maps better than language does onto the “symbolic” way in which human beings process information in their minds. Uniquely, as far as we can tell, we humans deconstruct our interior and exterior worlds into a vocabulary of discrete mental symbols. Once we have done this, we can shuffle those symbols around, according to rules, to produce statements not only about those worlds as they are but as they might be.

b. A Sensitive Period for Language Learning

Argument: Language has a critical period, because if you don't learn language when you are young, you will forever be language disadvantaged.

• Late vs. Early Second Language Learning
• Adults are better at learning vocabulary of new language, but children are better at learning grammar & pronunciation, for example, adult Chinese speakers learning English have major trouble with use of the articles "a" and "the" (Chinese has no articles). This is similar to findings with speakers of Slavic languages such as Russian which also do not have articles.
  

• Deaf children: Early learning of sign language = better use of sign language
  

• NOT IN BOOK: See, also, the experience of what are called "feral children" who "have spent much of their formative years in the wild, without any contact with other humans for a significant period of their lives" (Woodpigeon, 2000). In the few confirmed cases, these children experience significant social handicap and learn almost no language (not in book)

Conclusion 3: There is no language module which automatically causes a person to learn to speak. Rather the predisposing neural structures require social experience in the company of other people in order to develop most appropriately.

3. Language and the "Social Brain" Hypothesis (not in textbook)

a. Without rejecting the LAD theory above, we should note that language always arises within a social context and depends upon social interaction for its development (a corollary of the "critical period" observation). A purely biological explanation for the emergence of language is unlikely. Vasanta (2005) states this caution by claiming:

"...syntax-centered definitions of language knowledge [such as the LAD theory] completely ignore certain crucial aspects of language learning and use, namely, that language is embedded in a social context; that the role of environmental triggering as a learning mechanism is grossly underestimated; that a considerable extent of visuo-spatial information accompanies speech in day-to-day communication; that the developmental process itself lies at the heart of knowledge acquisition; and that there is a tremendous variation in the orthographic systems associated with different languages." (Abstract)

b. Contrary to the theory of the evolution of general intelligence, Robin Dunbar (U Liverpool, UK) and others propose that language developed as a way of helping organize larger and larger social grouping. This "social brain" hypothesis rests upon a variety of observations including two advantages conveyed by language:

• the ability to categorize individuals into distinct types (e.g., doctor, sheriff, chief)
• the ability to instruct other individuals about how they should respond "toward specific types of individuals within society" (Dunban, 1993)

Essentially, language permits societies of much larger size than would be possible otherwise. Such groups, e.g., bands, tribes, etc., have an survival advantage vis-a-vis those who do not have language.

c. Theory of Mind, Mental Time Travel, & Narrative as Factors in the Evolution of Language

• Recent theorists have proposed that there are some essential factors that contributed or drove the evolution of human language. These ideas are similar to what Dunbar and his colleagues have proposed in the "Social Mind" Hypothesis.
  

• "Theory of Mind" (TOM) = the ability to understand the intentions and goals of another person (or animal); an ability to predict what another person wants. Language (such as in the "Social Mind" Hypothesis) involves using our TOM abilities and communicates with others what we know. Mithen (2024) points out that there is no evidence that chimpanzees, our distant primate cousins, have any Theory of Mind about what other chimps are doing and, as such, do not have much experience in coordinating group activities as humans do via spoken language.
  

• Mental Time Travel (MTT) = our ability to go back in time to recall episodic memories (EM) and to project into the future what could or will be happening (episodic future thinking or EFT).  Much of what we communicate in language involves both EMs and EFTs.
  

• Narrative = putting together a story which has a past, a present, and a future (and, thus, depends upon MTT).  A great deal of the verbal interactions among human beings involves narrative. There are clear evolutionary advantages to the ability to remember the past, think about the future, and communicate those thoughts in the form of language shared with others.
  

D. When did human language evolve/develop?

  

A recent estimate of when our modern human species (Homo sapiens) evolved from earlier primate and hominid ancestors (Vidal et al., 2022) points to Eastern Africa 230 kya (+/- 22 kya; kya = "thousands of years ago"). Note in the map of Africa on the left above (Timbrell, 2024), the densest sites for tools and other human artifacts from the prehistoric period are found along the eastern side of the continent, particularly from the northeastern Ethiopian Highlands through the central Great Rift Valley down toward the southeastern hills of South Africa. Most archeologists of prehistory argue that H. sapiens originally emerged in the Great Rift Valley. Over the next 100-150 thousand years, H. sapiens migrated from Eastern Africa to spread throughout the rest of Africa, Asia, Europe, and Australia (I am omitting the migrations from Asia to the Americas which occurred ~20-15 kya)

According to estimates there are approximately 7,100 different languages spoken across the Earth among the 8 billion people populating the world.

Can we go backward in time to understand when human language first evolved or developed? The task is difficult:

“Since the emergence of language lies so far back in human prehistory, the relevant developments have left no direct historical traces, and comparable processes cannot be observed today” (https://en.wikipedia.org/wiki/Origin_of_language, April 18, 2025)

Nonetheless, it is notable that among all the languages spoken today, they "share striking similarities in the ways in which they are constructed phonologically, syntactically, and semantically" (Miyagawa et al. 2025 citing Eberhard et al. 2023). This suggests that despite so many different language there must be a common neurological and biological origin for human language itself. Thus, a strategy to detect when language developed would be to discover when the original Homo sapiens (modern humans) were last centered together in a common grouping, that is, before humans split apart and began to spread across the continents.

In order to determine when humans were last together as a common group, Miyagawa et al. (2025) used genetic markers from whole genomes of African populations (including Y chromosomes and mitochondrial DNA markers) to pinpoint when the first divergence in human populations occurred (it is known as the "Khosian divergence event"). The conclusion of their research states: "These genomic studies of early H. sapiens suggest that linguistic  potential must have been present in the H. sapiens population at the latest by 135kya" (p. 3; kya = thousand years ago). Miyagawa et al. (2025) elaborated on the meaning of their findings:

Based on the recent genetic studies of early H. sapiens, we have pinpointed approximately 135kya as the moment at which some linguistic capacity must have been present in the human population. Looking forward from this event, modern human behaviors such as body decoration and the production of ochre pieces with symbolic engravings appeared as normative and persistent behaviors around 100kya. We  believe that the time lag implied between the lower boundary of when language was present (135kya) and the emergence of normative modern human behaviors across the population suggests that language itself was the trigger that transformed nonlinguistic early H. sapiens (who nonetheless already possessed “language-ready” brains acquired at the origin of the anatomically distinctive species) into the symbolically-mediated beings familiar today. This development of the most sophisticated communication device in evolution allowed our ancestors to accelerate and consolidate symbolically-mediated behaviors until they became the norm for the entire species. (p. 4; emphases added).

Hence, we might conclude as they did that by 135,000 years ago, humans were "language ready" and over the subsequent tens of thousands of years actual languages emerged which expanded all of our behaviors that use symbols, the principal characteristic of the human species.

E. Strengths associated with human language.

Linguist and psychologist, Julie Sedivy (2024) points out three major strengths that humans achieve through our abilities to use language:

1. Language allows us to align our minds with those of others and represents a powerful method by which we can achieve connection with others.

2. Much of our experience of language comes from the intimate sensory settings in which we first learned words and concepts. Infants and young learn the sounds and words of their native language much more easily from those they know than from videos or other non-personal means. We acquire sensory memories and experiences that are tied up with the words we use.

3. Our linguistic abilities developed over a lifetime help us to overcome some of the limitations that come with the advances of old age (hearing loss, illness, stroke, etc.)

F. Brain Damage and Language

  1. Aphasia = Severe acquired language impairment due to damage to the brain's language areas (for most people in the left hemisphere)

Causes of aphasia include

• Stroke (ischemic or hemorrhagic)
• Traumatic brain injury (TBI), e.g., from automobile accident, falling & hitting head on ground
• Infectious diseases: meningitis, encephalitis, Herpex Simplex Virus (HSV), HIV, & various Streptococcus germs (especially causing an abscess in the brain)
• Brain tumors
• Progressive neurological disorders (Frontotemporal lobar degeneration [FTLD] & Alzheimer's disease)

 2a. Broca's Area: Small part of the frontal lobe of the left cerebral cortex that when damaged leads to impairments in language production.

  2b. Wernicke's Area

• Traditionally, Wernicke's Area has been located on the superior temporal cortex posterior to (behind) the Primary Auditory Cortex. Indeed, in our textbook, that is where the area is shown in a diagram. Damage to that area has usually been seen to lead to impairments in language comprehension.

• However, in the last decade with the coming of neuroimaging techniques to examine the brains of living persons with language impairments, a new understanding of what anatomical areas may be involved in this region has emerged. DeWitt & Rauchecker (2012) proposed that there is a region anterior to (in front of) the Primary Auditory Cortex that is involved in the recognition of speech sounds/phononlogical processing. And, going even further, Binder (2017) argues that it is damage to this anterior/medial area that is the cause of language comprehension loss.

• The traditional posterior superior temporal cortex that has been labeled "Wernicke's Area" seems to be primarily involved in “retrieval of phonological forms (mental representations of phoneme sequences), which are used for speech output and short-term memory tasks. Focal damage to this region produces phonemic paraphasia without impairing word comprehension” (Binder, 2017, Abstract, boldface & italics added). That term “phonemic paraphrasia” means the substitution of a word with a nonword that preserves at least half of the segments and/or number of syllables of the intended word, e.g., instead of saying “instructional resources” the person might say “instudinal desources”

    

  3. Broca's aphasia (or nonfluent aphasia): A language impairment whose most prominent symptom is a deficit in language production. Caused by damage to Broca' area and surrounding areas.

a. Patients suffering from Broca's aphasia often speak meaningfully, but omit pronouns, prepositions, conjunctions, and qualifiers from their own speech; they also have trouble understanding these same kinds of words. Other more seriously impaired individuals have significant difficulty forming the words themselves and will slur or otherwise produce difficult to understand language.

  Broca's aphasia - Sarah Scott - teenage stroke

  4. Wernicke's aphasia or fluent aphasia involves a difficulty in comprehending the verbal and written communications of others.  Although patients can still speak smoothly, their speech content is often nonsensical.  They also have anomia (difficulty recalling the names of objects). Note above the damage causing this may have nothing to do with "Wernicke's Area"

Wernicke's aphasia - Retired dentist

Wernicke's aphasia - Young woman (moderately impaired

  5. Language requires the activation of many different areas other than the frontal cortex (Broca's area and surrounding regions) and the temporal cortex.

     E. Dyslexia

1. Dyslexia: Inability to read or significant difficulty with reading despite adequate vision and intelligence.  Many kinds of dyslexia exist with different underlying causes. This is also a topic which has caused a great deal of argumentation and struggle among researchers, teachers, parents, and students for many decades.

• There is NO link between intelligence and dyslexia. Indeed there are many quite intelligent and successful people with dyslexia.
  
• Dyslexia is a condition that one does not "outgrow"
• Forms of dyslexia from mild to severe affects between 10% and 20% of the population
• Males and females show roughly equal percentages of dyslexic symptoms (dyslexia is NOT a "boy" problem).
• There appears to be a strong genetic component in dyslexia with the children of parents with dyslexia much more likely to develop the disorder.
  

2. D'Mello & Gabrieli (2018) summarize the key findings from fMRI and other studies. These suggest that individuals with dyslexia show....

• Underactivation in Verbal Word Form Area (in the fusiform gyrus of the left occipital-temporal cortex) "in response to world or work-like materials...[Further] reduced activation in this region is a persistent difference across both children and adults with dyslexia" (p. 801)

• "In children and adults with dyslexia, the left temporo-parietal cortex is consistently underactivated during phonological [sound] processing tasks consistent with the proposed role of this region in grapheme-to-phoneme mapping (mapping printed letters to individual sounds)" (pp. 801-802)

• "In contrast...studies often find increased engagement of the left inferior frontal region in dyslexia. Increased activation in this region could be associated with compensatory processes that may rely on covert or subvocal reading or an increased effort. Whereas typical readers show age-dependent decreases in activation in this region, readers with dyslexia show hyperactivation across ages" (p. 802)
  

3.  As a rule, a dyslexic person is more likely to have a bilaterally symmetrical cerebral cortex (i.e., the planum temporale and other structures are the same size on the left and right hemisphere).

• Temple and her colleagues (2003) found that, after behavioral intervention to teach dyslexic children better reading strategies, there was increased activation in the left temporo-parietal cortex that had previously been underactive.

4.  Other problems observed in persons with dyslexia (note that not all individuals with dyslexia shows all these problems):

a. Dysphonic dyslexia (dys = poor; phonos = sound) = difficulty sounding out printed words

b. Dyseidetic dyslexia (dys = poor; eidos = image) = difficulty recognizing words as a whole (though can sound them out)

c. Poor auditory memory: difficulty in remembering the sequence of sounds. Suggests that there may be a problem involving the connection between the visual and auditory processing areas of the brain.

c. Dyslexia is a function of attentional differences in which there are problems attending to information directly in front of the reader, that is, dyslexic readers have a fixation point 5 to 10 degrees to the right or left of the word in front of them. Check out the image on the right side.

Try to keep your eye fixated on the dot in the middle while you try to read the letters on either the right or the left of the dot. Individuals with dyslexia often find it easier to do so than those who do not have dyslexia.

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References

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The first version of this page was posted on April 24, 2005