Neurochemistry and Language

The ability to use language remains a unique characteristic of humans.  However, there is still much speculation as to the origin and development of language skills.  Recently, scientists have found that there may be a connection between language and human brain chemistry. 

Scientists have established several possibilities that could explain why language is a uniquely human trait and is not found in our primate relatives.  For instance, “comparative studies were conducted with respect to … [human and non-human primates’ abilities] to process grammars of different complexity” while “investigating the cytoarchitecture of particular brain areas and their structural connectivity” (Scharff).  So far, the current data available for analysis from this study points out that “non-human primates are able to learn simple probabilistic grammars, but not hierarchically structured complex grammars;” in comparison, the “human brain, which easily learns both grammars, differs from the non-human brain (among others) in how two language-relevant brain regions (Broca's area in the inferior frontal cortex and the superior temporal cortex) are connected structurally by fiber tracts which run dorsally and ventrally in the primate brain” (Scharff).   

 

Comparison of Broca's area

In addition, ontogenetic “findings suggest at least a correlation between the maturation of the dorsal pathway and the behavior to process syntactically complex structures, although” “the neural basis of complex grammar processing in humans remains to be defined” (Scharff).  Another interesting discovery lies within neurochemistry.  In the 1960s, physical anthropologist Ralph Holloway proposed that the “human brain must have reorganized its chemistry and wiring as early human ancestors began to walk upright, use tools, and develop more complex social networks 6 million to 2 million years ago—well before the brain began to enlarge 1.8 million years ago” (Gibbons).  However, “neurotransmitters aren’t preserved in ancient skulls,” so scientists have to rely on searching “for key differences in neurochemistry between humans and other primates living today” (Gibbons).  Biological anthropologist Mary Ann Raghanti conducted a comparative experiment doing just this.  Her colleagues and she “got tissue samples from brain banks and zoos of 38 individuals from six species who had died of natural causes: humans, tufted capuchins, pig-tailed macaques, olive baboons, gorillas, and chimpanzees” (Gibbons).  Then, they adhered to the following procedure:  First, they “sliced sections of basal ganglia" - to learn more about the basal ganglia, click the link at the end of this post - "clusters of nerve cells and fibers in a region at the base of the brain known as the striatum, which is a sort of clearinghouse that relays signals from different parts of the brain for movement, learning, and social behavior;” then, they “stained these slices with chemicals that react to different types of neurotransmitters, including dopamine, serotonin, and neuropeptide Y—which are associated with sensitivity to social cues and cooperative behavior;” finally, “they analyzed the slices to measure different levels of neurotransmitters that had been released when the primates were alive” (Gibbons).  Their results detailed that humans had a neurochemical combination that “‘is a key difference that sets apart humans from all other species;’” humans have “elevated levels of serotonin and neuropeptide Y, in the basal ganglia,” “dramatically more dopamine in their striatum,” and “less acetylcholine, a neurochemical linked to dominant and territorial behavior” (Gibbons). 

Neurochemistry of Basal Ganglia:  Serotonin and Neuropeptide Y

Raghanti’s study led paleoanthropologist Owen Lovejoy to theorize that the differences discovered in their neurochemistry “may have set in motion other evolutionary changes, such as the development of monogamy and language in humans” (Gibbons).  In turn, he proposed “a new “neurochemical hypothesis for the origin of hominids,” in which females mated more with males who were outgoing, but not too aggressive,” and “males who cooperated well with other males may have been more successful hunters and scavengers;” as “human ancestors got better at cooperating, they shared the know-how for making tools and eventually developed language—all in a feedback loop fueled by surging levels of dopamine” (Gibbons).  Lovejoy believes that “these neurochemical changes were already in place more than 4.4 million years ago, when Ardipithecus ramidus” existed (Gibbons).  However, criticisms of these findings note that the “neurochemistry of the brain is so complex, and dopamine is involved in so many functions that it’s hard to know precisely why natural selection favored higher dopamine levels—or even whether it was a side effect of some other adaptation;” nevertheless, the “research to quantify differences in neurochemistry among primates is important, especially as researchers study differences in gene expression in the brain” (Gibbons).  

Information about the basal ganglia:  https://www.coursera.org/lecture/medical-neuroscience/function-of-basal-ganglia-circuitry-57COe
 

Bibliography

Comparison of Broca's Area. ResearchGate, www.researchgate.net/figure/Human-brain-showing-Brocas-and-Wernickes-areas-upper-diagram-and-areas-of-chimpanzee_fig3_259919716.

Gibbons, Ann. “Dopamine may have given humans our social edge over other apes.” Science,

January 22, 2018. https://www.sciencemag.org/news/2018/01/dopamine-may-have-given-humans-our-social-edge-over-other-apes

“Neurochemistry in Basal Ganglia: Serotonin and Neuropeptide Y .” ClinicalGate , IKnowledge , clinicalgate.com/the-basal-ganglia/.

Scharff, Friederici, and Petrides. “Neurobiology of human language and its evolution: primate

           and non-primate perspectives.” Frontiers in Evolutionary Neuroscience 5, no. 1 (January          

           28, 2013): 1-2. doi:  [10.3389/fnevo.2013.00001]

FOXP2: Genetic Mutation

An unprecedented study, conducted at the Max Planck Institute for Evolutionary Anthropology, discovered that genetics may have played a role in the development of language in modern hominins. 

In 2002, scientist Svante Pääbo conducted an experiment that tested whether a gene, called FOXP2, had specific ties to language in modern hominins.  FOXP2 was discovered during a study of “a family who had a history of profound speech and language disorders;” “FOXP2 was the first gene found to be involved in language production” (Warren).  In the experiment, Pääbo and her colleagues “relied on a small set of 20 people on whom the researchers conducted Sanger sequencing of three FOXP2 introns;” this set was composed of “seven individuals from Africa, four from Europe, one from South America, five from Asia, and three from Australia and Papua New Guinea” (GenomeWeb).  After conducting the tests, their analysis discovered “that humans carry two mutations to FOXP2 not found in any other primates, and this genetic variation evidenced that a “‘selective sweep’ — in which a beneficial mutation quickly becomes common across a population” — occurred (Warren).  Pääbo also reported that this “change to FOXP2 seemed to have happened in the past 200,000 years” (Warren).  While her “paper has been cited hundreds of times in the scientific literature,” there are key elements to this experiment that have drawn criticism (Warren).  For instance, Pääbo conducted this experiment with a small data set of 20 people.  Especially for a discovery this monumental, she should have repeated her experiment with a larger data sample.  Brenda Henn, “a population geneticist at the University of California” and senior author from Stony Brook University, addressed this issue by stating her concerns “that an over-reliance on small data sets has skewed our understanding of what makes humans unique” (Warren).  In fact, Henn and researchers from Stony Book “‘wanted to test whether … [Pääbo’s] hypothesis stood up against a larger, more diverse dataset that more explicitly controlled for human demography’” (GenomeWeb).  Initially, Hen and her colleagues “did find an indication of positive selection on FOXP2;” however, “when they separated out African individuals and individuals whose ancestors underwent the out-of-Africa expansion, that signal disappeared” (GenomeWeb).  Henn’s findings led population geneticist and co-author of Pääbo’s paper, Elizabeth Atkinson, to reexamine Pääbo’s and Henn’s research; Atkinson then concluded that “the signal that had looked like a selective sweep in the 2002 study was probably a statistical artefact caused by lumping Africans together with Eurasians and other populations” and that the selective sweep thought to have been discovered cannot be verified (Warren).  In addition, another study “found that Neanderthals carried the same mutations” as modern hominins, suggesting “that the modifications to FOXP2 happened before the two groups split, more than half a million years ago” (Warren).  

FOXP2

Nevertheless, Simon Fisher, “director of the Max Planck Institute for Psycholinguistics in Nijmegen, the Netherlands, and a coauthor of the 2002 study,” affirms that even “if there was no recent evolution of FOXP2, there is still plenty of evidence that the gene is involved in language” (Warren).  That is, it is evidential that mutations “in FOXP2 cause language disorders in humans, and in mice the gene is important for vocalizations and movement — both functions that are crucial to human speech” (Warren).  Fisher also states that FOXP2 is only “‘one piece of a complex puzzle,’” which can only be solved through further delving into the complex genetics of language and continuing to conduct experiments on a diverse sample of people (Warren).  

Bibliography

“FOXP2 .” Cell, Cell, www.cell.com/cell/fulltext/S0092-8674(18)30851-1.

GenomeWeb. “New Analysis Fails to Find Recent, Human-Specific Selection at Language-

Linked FOXP2 Gene.” Accessed October 25, 2018. https://www.genomeweb.com/genetic-research/new-analysis-fails-find-recent-human-specific-selection-language-linked-foxp2-gene#.W9Mu7lJReYU

Warren, Matthew. “Diverse genome study upends understanding of how language evolved.”

Nature, August 2, 2018. https://www.nature.com/articles/d41586-018-05859-7

Bengalese Finches And An Hypothesis On Language Origins

Recent research has found that "evolution and [the] development of language are ... inherently related," an observation that is backed up by the theory of evolutionary developmental biology (Oller 1).  This theory "emphasizes the idea that no structure or capability can be evolved without being developed, and that consequently the targets of natural selection are often, if not usually, developmental processes or systems" (Oller 1).  That is, a species cannot evolve if there is no developmental growth, which occurs through the process of natural selection.    

As the origin of the development of language is still a mystery, scientists believe they may have come across a potential possibility, an hypothesis that is based off of observations of Bengalese finches. 

Bengalese finches are known to be friendly and sing beautiful, complex melodies.  These characteristics juxtapose its ancestor, the white-rumped munia, as munias are aggressive and whistle “a scratchy, off-kilter tune” (Erard). 

                                                        Figure 1:  White-rumped munia             

Figure 2:  Bengalese finch

This turnabout in behavior sparked the self-domestication hypothesis.  This hypothesis states that “skills such as learning complex calls, combining vocalizations, and simply knowing when another creature wants to communicate all came about as a consequence of pro-social traits like kindness” (Erard).  In connection to human evolution, scientists postulate that “the building blocks of language are a byproduct of brain alterations that arose when natural selection favored cooperation among early humans” (Erard).  According to Charles Darwin, this desire for cooperation over aggression amongst early humans’ social interactions led to not only behavioral changes, that humans “essentially domesticated themselves,” but also evolutionary changes, specifically “lower levels of circulating androgens (such as testosterone) that tend to promote aggression” (Erard).  As testosterone decreased, neurohormones, including serotonin, increased and aided in humans’ abilities to “infer others' mental states, learn through joint attention, and even link objects and labels—all prerequisites for language” (Erard). 

Focusing back, ornithologist Kazuo Okanoya, from the Riken Center for Brain Science in Wako, Japan, did an intensive quantitative study on the relationship between Bengalese finches and white-rumped munias to language.  According to Okanoya, while both birds are vocal learners, munia “songs tend to be shorter, simpler, and full of unmelodic segments of acoustic "noise," compared with the longer, louder finch songs, which contain peeps, chirps, and segments that often repeat and recombine in improvisational ways” (Erard).  He proposes that this change occurred behaviorally, as the finches were being domesticated and living in a “relatively stress-free environment,” as well as biologically, as tests show that “finches have lower fecal levels of corticosterone —a hormone that boosts aggressiveness and blunts cognitive functioning in birds;” high levels of corticosterone “inhibit the growth of neurons in the birds' song-learning system, which is larger in the finches than in the munia” (Erard).  Furthermore, the language/song abilities of finches forwarded natural selection through mating:  Okanoya suggests that, “because attention-getting songs help advertise fitness to females, the males best at learning and singing would be most likely to pass their genes on to the next generation” (Erard).  In association to the finches, evolutionary linguist Simon Kirby speculates that if “early humans somehow developed their own lower-stress "domesticated" environment—perhaps as a result of easier access to food—it could have fostered more cooperation and reduced aggression” (Erard). 

Bibliography

Bengalese Finch . EFinch, www.efinch.com/species/society.htm.

Erard and Matacic. “Can these birds explain how language first evolved?” Science, August 2,

2018. http://www.sciencemag.org/news/2018/08/can-these-birds-explain-how-language-first-evolved.

Oller, Dale, and Griebel. “New Frontiers in Language Evolution and Development:
Introduction to the topiCS Volume.” Top Cogn Sci. 8, no. 2 (April 2016): 353-360. doi:10.1111/tops.12204
“White-Rumped Munia.” The Internet Bird IBC Bird Collection , www.hbw.com/ibc/species/white-rumped-munia-lonchura-striata.

Welcome!

Hello!  Welcome to Anthrobiolinguists! 
As a linguist-in-training, I am interested in learning all things concerning the scientific study of language.  Besides the theoretical and applied facets of the field, there is a lot of overlap between linguistics and anthropology.  Specifically, biological anthropology has a significant role in explaining the biological functions behind language development and phonetics, which focuses on the development and classification of speech sounds.  In this blog, I aim to examine current events related to this connection between biological anthropology and linguistics. 

Thanks for reading!