Neurobiological origins of language

Last updated

Language has a long evolutionary history and is closely related to the brain, but what makes the human brain uniquely adapted to language is unclear. The regions of the brain that are involved in language in humans have similar analogues in apes and monkeys, and yet they do not use language. There may also be a genetic component: mutations in the FOXP2 gene prevent humans from constructing complete sentences. [1]

Contents

Neurobiological adaptations for language

Broca's and Wernicke's areas

These regions are where language is located in the brain – everything from speech to reading and writing. [2] Language itself is based on symbols used to represent concepts in the world, and this system appears to be housed in these areas. The language regions in human brains highly resemble similar regions in other primates, even though humans are the only species that use language. [3]

The brain structures of chimpanzees are very similar to those of humans. Both contain Broca's and Wernicke's homologues that are involved in communication. Broca's area is largely used for planning and producing vocalizations in both chimpanzees and humans. Wernicke's area appears to be where linguistic representations and symbols are mapped to specific concepts. This functionality is present in both chimpanzees and humans; the chimpanzee Wernicke's area is much more similar to its human counterpart than is the Broca's area, suggesting that Wernicke's is more evolutionary ancient than Broca's. [4]

Motor neurons

Sagittal section of human vocal tract Sagittalmouth.png
Sagittal section of human vocal tract

In order to speak, the breathing system must be voluntarily repurposed to produce vocal sounds, [3] which allows the breathing mechanisms to be temporarily deactivated in favor of song or speech production. The human vocal tract has evolved to be more suited to speaking, with a lower larynx, 90° turn in the windpipe, and large, round tongue. [5] Motor neurons in birds and humans bypass the unconscious systems in the brainstem to give direct control of the larynx to the brain. [6]

Theories of language origin

Gestural origin

The earliest language was strictly vocal; reading and writing came later. [3] New research suggests that the combination of gestures and vocalizations may have led to the development of more complicated language in protohumans. Chimpanzees that produce attention-getting sounds show activation in areas of the brain that are highly similar to Broca's area in humans. [7] [8] Even hand and mouth movements with no vocalizations cause very similar activation patterns in the Broca's area of both humans and monkeys. [4] When monkeys view other monkeys gesturing, mirror neurons in the Broca's homologue activate. Groups of mirror neurons are specialized to respond only to one kind of viewed action, and it is currently believed that these may be an evolutionary origin to the neurons that are adapted for speech processing and production. [9]

Universal grammar

The language bioprogram hypothesis proposes that humans have an innate, cognitive grammatical structure allowing them to develop and understand language. According to this theory, this system is embedded in human genetics and underpins the basic grammar of all languages. [4] Some evidence suggests that at least some of our linguistic capacities may be genetically controlled. Mutations in the FOXP2 gene prevent people from combining words and phrases into sentences. [1] However, these genes are present in the heart, lungs, and brain, and their role is not entirely clear. [1]

It is possible that the human capacity for grammar evolved from non-semantic behavior like singing. [10] Birds have the ability to produce, process, and learn complex vocalizations, but the units of a birdsong, when removed from the larger meaning and context of the birdsong as a whole, have no inherent meaning. Early hominids may have evolved capacities for similar, non-semantic purposes, that were later modified for symbolic language. [6]

See also

Related Research Articles

<i>Ardipithecus</i> Extinct genus of hominins

Ardipithecus is a genus of an extinct hominine that lived during the Late Miocene and Early Pliocene epochs in the Afar Depression, Ethiopia. Originally described as one of the earliest ancestors of humans after they diverged from the chimpanzees, the relation of this genus to human ancestors and whether it is a hominin is now a matter of debate. Two fossil species are described in the literature: A. ramidus, which lived about 4.4 million years ago during the early Pliocene, and A. kadabba, dated to approximately 5.6 million years ago. Behavioral analysis showed that Ardipithecus could be very similar to chimpanzees, indicating that the early human ancestors were very chimpanzee-like in behavior.

Language center speech processing in the brain

In neuroscience and psychology, the term language center refers collectively to the areas of the brain which serve a particular function for speech processing and production. Language is a core system, which gives humans the capacity to solve difficult problems and provides them with a unique type of social interaction. Language allows individuals to attribute symbols to specific concepts and display them through sentences and phrases that follow proper grammatical rules. Moreover, speech is the mechanism in which language is orally expressed.

Brocas area Speech production region in the dominant hemisphere of the hominid brain

Broca's area, or the Broca area, is a region in the frontal lobe of the dominant hemisphere, usually the left, of the brain with functions linked to speech production.

Aphasiology is the study of language impairment usually resulting from brain damage, due to neurovascular accident—hemorrhage, stroke—or associated with a variety of neurodegenerative diseases, including different types of dementia. It is also the name of a scientific journal covering the area. These specific language deficits, termed aphasias, may be defined as impairments of language production or comprehension that cannot be attributed to trivial causes such as deafness or oral paralysis. A number of aphasias have been described, but two are best known: expressive aphasia and receptive aphasia.

FOXP2 Transcription factor gene of the forkhead box family

Forkhead box protein P2 (FOXP2) is a protein that, in humans, is encoded by the FOXP2 gene. FOXP2 is a member of the forkhead box family of transcription factors, proteins that regulate gene expression by binding to DNA. It is expressed in the brain, heart, lungs and digestive system.

Bird vocalization Sounds birds use to communicate

Bird vocalization includes both bird calls and bird songs. In non-technical use, bird songs are the bird sounds that are melodious to the human ear. In ornithology and birding, songs are distinguished by function from calls.

Brodmann area 45

Brodmann area 45 (BA45), is part of the frontal cortex in the human brain. It is situated on the lateral surface, inferior to BA9 and adjacent to BA46.

Brodmann area 47

Brodmann area 47, or BA47, is part of the frontal cortex in the human brain. It curves from the lateral surface of the frontal lobe into the ventral (orbital) frontal cortex. It is below areas BA10 and BA45, and beside BA11. This cytoarchitectonic region most closely corresponds to the gyral region the orbital part of inferior frontal gyrus, although these regions are not equivalent. Pars orbitalis is not based on cytoarchitectonic distinctions, and rather is defined according to gross anatomical landmarks. Despite a clear distinction, these two terms are often used liberally in peer-reviewed research journals.

Wernickes area Speech comprehension region in the dominant hemisphere of the hominid brain

Wernicke's area, also called Wernicke's speech area, is one of the two parts of the cerebral cortex that are linked to speech, the other being Broca's area. It is involved in the comprehension of written and spoken language, in contrast to Broca's area, which is involved in the production of language. It is traditionally thought to reside in Brodmann area 22, which is located in the superior temporal gyrus in the dominant cerebral hemisphere, which is the left hemisphere in about 95% of right-handed individuals and 70% of left-handed individuals.

The origin of language, its relationship with human evolution, and its consequences have been subjects of study for centuries. Scholars wishing to study the origins of language must draw inferences from evidence such as the fossil record, archaeological evidence, contemporary language diversity, studies of language acquisition and comparisons between human language and systems of communication existing among animals. Many argue that the origins of language probably relate closely to the origins of modern human behavior, but there is little agreement about the facts and implications of this connection.

Language processing in the brain

Language processing refers to the way humans use words to communicate ideas and feelings, and how such communications are processed and understood. Language processing is considered to be a uniquely human ability that is not produced with the same grammatical understanding or systematicity in even human's closest primate relatives.

Brodmann area 22

Brodmann area 22 is a Brodmann's area that is cytoarchitecturally located in the posterior superior temporal gyrus of the brain. In the left cerebral hemisphere, it is one portion of Wernicke's area. The left hemisphere BA22 helps with generation and understanding of individual words. On the right side of the brain, BA22 helps to discriminate pitch and sound intensity, both of which are necessary to perceive melody and prosody. Wernicke's area is active in processing language and consists of the left Brodmann area 22 and Brodmann area 40, the supramarginal gyrus.

The evolution of intelligence is closely tied to the evolution of the human brain and to the origin of language. The timeline of human evolution spans approximately 9 million years, from the separation of the genus Pan until the emergence of behavioral modernity by 50,000 years ago. The first 3 million years of this timeline concern Sahelanthropus, the following 2 million concern Australopithecus and the final 2 million span the history of the genus Homo in the Paleolithic era.

Speech Human vocal communication using spoken language

Speech is human vocal communication using language. Each language uses phonetic combinations of vowel and consonant sounds that form the sound of its words, and using those words in their semantic character as words in the lexicon of a language according to the syntactic constraints that govern lexical words' function in a sentence. In speaking, speakers perform many different intentional speech acts, e.g., informing, declaring, asking, persuading, directing, and can use enunciation, intonation, degrees of loudness, tempo, and other non-representational or paralinguistic aspects of vocalization to convey meaning. In their speech speakers also unintentionally communicate many aspects of their social position such as sex, age, place of origin, physical states, psychic states, physico-psychic states, education or experience, and the like.

Lateralization of brain function Specialization of some cognitive functions in one side of the brain

The lateralization of brain function is the tendency for some neural functions or cognitive processes to be specialized to one side of the brain or the other. The medial longitudinal fissure separates the human brain into two distinct cerebral hemispheres, connected by the corpus callosum. Although the macrostructure of the two hemispheres appears to be almost identical, different composition of neuronal networks allows for specialized function that is different in each hemisphere.

Vocal learning is the ability to modify acoustic and syntactic sounds, acquire new sounds via imitation, and produce vocalizations. "Vocalizations" in this case refers only to sounds generated by the vocal organ as opposed to by the lips, teeth, and tongue, which require substantially less motor control. A rare trait, vocal learning is a critical substrate for spoken language and has only been detected in eight animal groups despite the wide array of vocalizing species; these include humans, bats, cetaceans, pinnipeds, elephants, and three distantly related bird groups including songbirds, parrots, and hummingbirds. Vocal learning is distinct from auditory learning, or the ability to form memories of sounds heard, a relatively common trait which is present in all vertebrates tested. For example, dogs can be trained to understand the word "sit" even though the human word is not in its innate auditory repertoire. However, the dog cannot imitate and produce the word "sit" itself as vocal learners can.

The principles that govern the evolution of brain structure are not well understood. Brain to body size scales allometrically. Small bodied mammals have relatively large brains compared to their bodies whereas large mammals have smaller brain to body ratios. If brain weight is plotted against body weight for primates, the regression line of the sample points can indicate the brain power of a primate species. Lemurs for example fall below this line which means that for a primate of equivalent size, we would expect a larger brain size. Humans lie well above the line indicating that humans are more encephalized than lemurs. In fact, humans are more encephalized than all other primates.

Lunate sulcus

In brain anatomy, the lunate sulcus or simian sulcus also known as the sulcus lunatus is a fissure in the occipital lobe variably found in humans and more often larger when present in apes and monkeys. The lunate sulcus marks the transition between V1 and V2.

The origin of speech refers to the general problem of the origin of language in the context of the physiological development of the human speech organs such as the tongue, lips and vocal organs used to produce phonological units in all human languages.

Evolutionary psychology of language is the study of the evolutionary history of language as a psychological faculty within the discipline of evolutionary psychology. It makes the assumption that language is the result of a Darwinian adaptation.

References

  1. 1 2 3 Marcus, G.; Rabagliati, H. (2006). "What developmental disorders can tell us about the nature and origins of language". Nature Neuroscience. 9 (10): 1226–1229. doi:10.1038/nn1766. PMID   17001342. S2CID   14663758.
  2. Hoff, E (2009). Language Development. Belmont, CA: Wadsworth. ISBN   978-0-495-50171-8.
  3. 1 2 3 Boulton, David. "Terrence Deacon, Ph.D. - The Co-evolution of Language and the Brain" . Retrieved 15 March 2012.
  4. 1 2 3 Falk, D. "The Evolution of Broca's Area".[ permanent dead link ]
  5. Anderson, Stephen (2004). Doctor Dolittle's Delusion. London: Yale University Press. pp. 25–26. ISBN   978-0-300-10339-7.
  6. 1 2 Sereno, M. I. (2005). "Language origins without the semantic urge" (PDF). Cognitive Science Online. 3 (1): 1–12.
  7. Arbib, M.; Bota, M. (2003). "Language evolution: neural homologies and neuroimformatics". Neural Networks. 16 (9): 1237–1260. CiteSeerX   10.1.1.100.9328 . doi:10.1016/j.neunet.2003.08.002. PMID   14622882.
  8. Taglialatela, J. P.; Russell, J. L.; Schaeffer, J. A.; Hopkins, W. D. (20 April 2011). "Chimpanzee Vocal Signaling Points to a Multimodal Origin of Human Language". PLOS ONE. 4. 6 (4): e18852. Bibcode:2011PLoSO...618852T. doi: 10.1371/journal.pone.0018852 . PMC   3080370 . PMID   21533079.
  9. Fadiga, L; Craighero, L.; D'Ausilio, A (2009). "Broca's Area in Language, Action, and Music". The Neurosciences and Music III—Disorders and Plasticity. 1169 (1): 448–458. Bibcode:2009NYASA1169..448F. doi:10.1111/j.1749-6632.2009.04582.x. PMID   19673823. S2CID   10596728.
  10. Deacon, TW (11 May 2010). "Colloquium paper: a role for relaxed selection in the evolution of the language capacity". Proceedings of the National Academy of Sciences of the United States of America. 107 Suppl 2: 9000–6. Bibcode:2010PNAS..107.9000D. doi: 10.1073/pnas.0914624107 . PMC   3024028 . PMID   20445088.

Bibliography

External references