If speech is an evolutionary acquisition of man, it must also have a genetic basis. It is a common fact that only 1% distinguishes us from the closest relative among great apes genetic material. It seems that this is quite a bit, but sorting through the entire genome in search of differences of interest is not so simple. This approach does not yet bring stunning discoveries: most of the differences found are functionally neutral. Therefore, the genetics of the "most human" features, which include speech, for the most part remains unknown. However, another approach is available to us: determining the genetic basis of pathology in patients with impaired function of interest to us. Everything that is known today about the genetics of speech has been revealed in this way.
KE family
In the 1990s, one British family, which in the literature is called KE, came to the attention of scientists. In this family, a rather severe speech disorder occurred in three generations, and it was inherited as an autosomal dominant trait. This discovery caused a huge stir: some scientists were quick to conclude that we are close to discovering a “speech gene” or even a “grammar gene”. Long before biology could confirm or disprove this, Noam Chomsky insisted that there was some kind of innate language acquisition mechanism (language acquisition device), already "sharpened" for a universal grammar, "knowing" the general principles of the language in advance and only waiting for a specific language environment . But if the mechanism is innate, it will have a genetic basis - and all the eyes of those hoping to find these reasons turned to the KE family.
First, a neuropsychological examination was performed. It turned out that all family members, including those who did not suffer from a speech disorder, had an IQ that was below average. That is, firstly, the described speech disorder is not quite specific, and some manifestations may be due to mental retardation. Secondly, special speech tests also did not confirm the hypothesis that the ability to use grammatical rules is affected. Rather, the patients had difficulties with coordination of movements, control of the muscles of the orofacial zone. At the same time, the disorder had the character of apraxia, that is, a violation of the development of motor programs, but specifically in relation to speech; since then it has been appropriately named: children's apraxia of speech. But it is interesting that defects were found not only in oral speech, but also in writing, and also involved the perception of speech (it is known that reference to our own, internal motor programs is necessary for the perception of someone else's speech). Neuroimaging studies have shown that there was a brain developmental disorder that resulted in morphologically detectable changes in the size of certain structures, including the subcortical nuclei and the cerebellum.
Nevertheless, the connection with the function of speech was obvious, and this was the only "genetic clue" that ended up in the hands of scientists. At the end of the nineties, the search for genetic structures that would cause speech disorders in the KE family began. First, they found that chromosome 7 differs in its structure, then - its specific section, where the gene was presumably localized. It was named SPCH1 - and, finally, using data from another clinical case, the gene itself was found - FOXP2.
FOXP2 in evolution
The FOXP2 product is a transcription factor, that is, it regulates the expression of other genes. It binds directly to the DNA region containing these genes, which affects the likelihood of their transcription. A feature of this protein is a structural motif - a fork-shaped domain (forkhead-box, or, in short, FOX domain), which binds to DNA.
Apparently, the gene is involved in functions more important than speech. This is indicated by the absence in the human population of individuals in whom both copies of FOXP2 would be damaged. In addition, evolutionary studies have found that this gene is highly conserved in mammals: in chimpanzees, gorillas, and rhesus macaques, it differs by only one amino acid substitution from its ortholog in mice. The corresponding monkey gene differs from the human ortholog by two amino acid substitutions. However, more significant differences are revealed in the nature of expression: for example, in humans, the repeating sequence of glutamine molecules varies in length, while this feature is not observed in chimpanzees. In addition, it was noted that in humans, compared with probabilistic calculations, the number of active substitutions is higher than silent substitutions (silent mutations do not lead to a change in the amino acid sequence). This indicates that there was a selection in favor of the human variant of the FOXP2 gene, that is, it could be at least one of the genes that determined the emergence of language abilities in evolution.
An analysis of the variability of the FOXP2 intron in different human populations made it possible to approximately estimate the time of appearance of the mutation that led the gene to modern look. This happened about 220 thousand years ago, that is, during the formation of a person of the modern anatomical type (CHSAT), Homo Sapiens. However, later it turned out that FOXP2 looked the same in Neanderthals, that is, the gene should have appeared during the existence of a common ancestor of Neanderthal and PCAT, about 300-400 thousand years ago. However, the dating methods themselves require additional verification.
FOXP2 in mice
The researchers' next step was to study the functions of FOXP2, and since it only differs in a few amino acid substitutions in mice, they appear to be a useful model. Among the effects of Foxp2 knockout (in the mouse version, its spelling is somewhat different) are those associated with vocalization: such animals are less likely to spontaneously give voice - but they are controversial, and far from being in the first place. During embryogenesis in Foxp2 knockout mice, the growth and branching of neurons are impaired, and the direction of axon growth is distorted. Mice with a "turned off" gene live 3-4 weeks, slowly gain weight and do not
reach normal sizes, have multiple motor disorders, which is explained by delayed maturation of the cerebellum. Humans do not show neurological symptoms associated with FOXP2 defects other than the cognitive deficits mentioned.
It is possible that the lethality of the absence of normal copies of the FOXP2 gene (and its homologue in mice) is due to its effects in other tissues, such as heart and lung. The gene is mainly expressed in the deep layers of the cortex, Purkinje cells of the cerebellum, and in medium-sized spiny neurons in the striatum.
Another experiment was to create in mice the same mutation in FOXP2, which led to a disease in the KE family (and also in a heterozygous state). The consequences of such a replacement are studied in more detail at the tissue level. Changed is synaptic plasticity in cortico-striatal and -cerebellar connections; in the glutamatergic synapses of spiny neurons of the striatum, long-term depression was observed less frequently than normal. Accordingly, the level of basal activity of these neurons in electrophysiological studies was increased, which is consistent with the results of neuroimaging in the KE itself: it also demonstrated striatal dysfunction.
The studies of FoxP2 in birds are interesting: although their version of the gene is more different from the human one, its clear connection with vocalization has been demonstrated. The gene is highly expressed in the striatum, which is part of the neural network responsible for vocalization in songbirds. On the zebra finches, it was possible to show that if the expression of the gene is artificially reduced by molecular genetic methods, the chick learns its species song incompletely and in a distorted form.
Targets FOXP2
If FOXP2 is a transcription factor, then genes that directly affect the formation of speech should be among its targets. Several such genes are actually known:
– CNTNAP2 (Contactin-associated protein-like 2) encodes the transmembrane protein CASPR2, which belongs to the neurexin superfamily and mediates intercellular interactions. The association of various mutations in this gene with autism, schizophrenia, epilepsy, and Tourette's syndrome has been demonstrated. All carriers of these mutations share the same phenotypic traits—mental retardation, seizures, autistic behavior, and speech disorders—and each of these traits can range in severity from mild to disabling. The speech disorders we are interested in are manifested by a delay speech development, complete lack of speech and dysarthria. The most studied is the association of one of the SNPs (single nucleotide polymorphism, single nucleotide polymorphism) with specific language impairment (SLI), a disease in which speech is impaired in the absence of hearing impairments and autistic features. High level CNTNAP2 expression is observed in layers II-IV of the cortex of Broca's area and areas surrounding the Sylvian furrow.
– the SRPX2 and uPAR genes function in a complex, and FOXP2 regulates the expression of both. The SRPX2 gene is associated with Rollandic epilepsy and apraxia of speech; morphologically, such patients often have microgyria in the region of the Sylvian sulcus. It has been shown in mice that it is the expression of SRPX2 that affects the formation of excitatory synapses and spines, i.e., a disturbance in this link may be due to the corresponding effect of FOXP2 knockout in mice. The uPAR gene encodes the plasminogen activator receptor, which is involved in the SRPX2 effect.
– among the genes whose expression is controlled by FOXP2, there are candidate genes for autism, for example, MET or MEF2C. The function of MEF2C (myocyte enhancer factor 2C) is presumably to downregulate (i.e. suppress) the formation of dendritic spines and excitatory synapses in hippocampal neurons; the same thing happened in the experiment in cultured striatum cells. Since FOXP2 reduces MEF2C expression, its dysfunction leads to the opposite effect, which is consistent with the above data: in FOXP2 knockout mice, we see hyperactivity of striatal neurons. In ontogeny, this leads to the formation of corticostriatal connections in a different volume than it normally does. The MET gene encodes a tyrosine kinase receptor that is involved in many processes during embryogenesis. Regarding neurogenesis, it is known that this gene is actively expressed in neuronal growth cones at early stages of development, and its activation involves the small GTPase Cdc42 and stimulates neuron growth, dendritic branching, and spine formation. Inactivation of MET in the experiment led to the formation of altered neurons, which corresponded in structure to the early stages of maturation. If the activation of MET in embryogenesis was prolonged, this suppressed the formation and maturation of glutamatergic synapses. Attempts to manipulate the level of MET expression in the neurons of the prefrontal region led to a violation of the formation neural networks in which these neurons are usually involved.
– the DISC-1 (Disrupted in Schizophrenia) gene was originally studied as a possible cause of schizophrenia, but is currently being studied in many other mental disorders, including affective, mental retardation, and autism. Its functions are poorly understood, but it is assumed that it is also necessary for synaptogenesis.
Other diseases, other genes
In addition to FOXP2 and its team, other genes are also found, the damage of which affects various aspects of speech proficiency. It is clear that only one gene, even if it is a transcription factor, could not entirely determine the development of language and give human evolution such a sharp turn. Apparently, this happened slowly and required many modifications.
Among children's mental disorders, there is a special section dedicated specifically to speech disorders. Since it is a genetically determined pathology that often manifests itself in childhood, the genetic basis of specific childhood speech disorders has been studied quite well.
1. Developmental dyslexia (reading disability) - Difficulties with pronunciation and reading that cannot be explained by other obvious causes, such as low IQ or physical disabilities, as well as learning disabilities. Affects 5-10% of children school age, and in adulthood, difficulties persist. Often there are difficulties with understanding speech, which are revealed by more subtle tests.
In genome-wide studies, 9 DYX1-9 regions have been identified that may be associated with the development of this disease. In three of them, specific genes are localized:
– In the DYX1 region, the DYX1C1 gene. The functions of this gene include the migration of neurons, the organization of the cytoskeleton. In post-mortem studies of the brains of people with DYX1C1 mutations in the left hemisphere, mild malformations associated with dystopic neurons and glia were found.
– The DYX2 region contains the KIAA0319 and DCDC2 genes. The KIAA0319 gene encodes a membrane protein with a large extracellular domain required for neuronal adhesion. DCDC2 encodes one of the domains of doublecortin (a protein expressed by immature neurons, a marker of neurogenesis) and is required for cytoskeletal-mediated intracellular dynamics.
– In the DYX5 region, the ROBO1 gene, which encodes a directing receptor for axons crossing the midline. Its mutations, respectively, lead to the formation of dysfunctional interhemispheric connections.
2. specific disorder speech - not due to other reasons, the inability to master colloquial speech, which affects one of its important aspects: morphology, syntax, pragmatics or semantics. Both speech reproduction and perception may be impaired, and written speech. The disease affects up to 7% of children aged 5-6 years. With age, the deficit is corrected, but deviations in complex tests remain in adulthood. We have already mentioned one of the candidate genes for this disorder, CNTNAP2. Two more were localized on chromosome 16: CMIP and ATP2C2. CMIP encodes a protein that enters the cytoskeleton, and, except in SPP, its mutations occur in patients with autism. ATP2C2 encodes calcium ATPase and is involved in the regulation of cellular levels of magnesium and calcium.
3. Children's apraxia of speech - a disorder that was described at the beginning of the material, it was it that helped to detect the FOXP2 gene. However, later it turned out that only a small percentage of patients who meet the criteria for this disorder have damage in the FOXP2 gene, that is, most cases of childhood apraxia of speech must be due to other causes.
4. Disorder of sound pronunciation - difficulties with the reproduction and correct use of speech sounds, which are most often manifested by omissions and substitutions of sounds that are significant for understanding the meaning. This phenomenon is very often observed in young children who are just learning to speak. It is considered pathological if it persists by the age of six - this occurs in about 4% of cases. This disorder is difficult to distinguish from childhood apraxia and specific
speech disorder. May have a common genetic basis with dyslexia, as the most significant association is found with changes in the DYX5 region.
5. Stuttering - involuntary repetition and lengthening of syllables, pauses that violate the smoothness of speech. Usually resolves with age, but about 20% of patients continue to stutter into adulthood. Semantic and grammatical characteristics of speech, as a rule, are not violated. A relationship has been found with three genes involved in object recognition for lysosome enzymes: GNPTAB, GNPTG, and NAGPA. All three genes encode subunits of the enzyme N-acentyl-glucosamine-1-phosphotransferase, which is necessary for the "marking" of oligosaccharides containing mannose and subsequent recognition by lysosomes. These genes may also be associated with a more serious disease than stuttering - mucolipidosis types 2 and 3.
A complex of MCPH and ASPM genes is also known, defects in which lead to microcephaly. In such patients, language development does not exceed the level of a six-year-old child. However, they do have basic language skills, which again leads us to the importance of the internal structure of the brain, not its size. MCPH encodes the protein microcephalin, which is involved in the organization of the cell cycle and DNA repair before division. The ASPM product is necessary for the construction of division spindles and ensures the symmetry of the resulting cells. Interestingly, defective variants of these genes are rare in Africa, where tonal languages are common, and often (up to 30%) in Europe, where this type of language is not.
How is it that we humans can talk and our rather close relatives, chimpanzees, can't? American experts conducted a large-scale study, during which they tried to figure out what became the real reason such a critical difference. Is the development of the brain over the years so important, or is our genes responsible for everything?
Verbal communication between people is considered one of the main distinguishing features of man, separating him from the rest of the animal world. Let this boundary be conditional, and animals still have certain manifestations of speech (as well as awareness, perception of spoken and audible sounds). But the indisputable fact is that they do not reach the level of a person.
What is the uniqueness Homo sapiens, decided to find out for certain genetics from the Universities of California in Los Angeles (UCLA) and Emory (Emory University). They suggested that our genes are "to blame". However, scientists in this were, of course, far from the first, but this group of specialists for the first time conducted such an extensive study of the genetic basis of the appearance of speech in humans.
It has long been known that the central gene responsible for the correct development of speech in humans is FOXP2. This gene encodes a protein of the same name, thanks to which FOXP2 can control the work of other genes.
Previous research has shown that when this gene is inactivated, people develop severe problems with speech (forming phrases) and pronunciation of sounds.
However, FOXP2 is also present in some animals (birds, reptiles, and even fish). Logically, it turns out that it is not he who is responsible for the appearance of speech in a person. Some scientific groups began to look for other "speech genes", others continued to study in detail the work of FOXP2.
Further research showed that FOXP2 remained almost unchanged during mammalian evolution (up to the time of the separation of humans and chimpanzees). However, about 200 thousand years ago, the gene began to acquire its "human" features.
The latter was established by a group of German scientists in 2002. Biologists then discovered that in chimpanzees, the proteins encoded by the version of this gene have some differences from humans. This could mean that FOXP2 functions differently in humans. Hence the unique linguistic abilities.
Another step towards understanding the ongoing processes was made this year by geneticists from the Max Planck Institute for Evolutionary Anthropology (Max-Planck-Institut für evolutionäre Anthropologie). They inserted the human version of the gene into mouse DNA.
Of course, rodents did not speak like a human because of this: after all, the ability to speak is a complex skill. But studies conducted then showed that the vocalization of animals has changed. In addition, in the regions of the brain of mice (those associated with speech in humans), neurons have changed their structure and activity. And this is already something!
A more detailed study was taken up by a group of scientists led by Genevieve Konopka and Daniel Geschwind from the University of California at Los Angeles. Biologists have grown colonies of brain cells in Petri dishes that lack the FOXP2 gene.
Then one part of the cells was introduced with the human version of the gene, and the second - from the chimpanzee. After that, the specialists followed the expression of genes, the process of translating DNA information into working proteins of the cell, and registered which genes and how these changes were reflected.
In their article in the journal Nature, scientists write that out of hundreds of genes subject to FOXP2, they were able to isolate 116 that reacted to the activation of the human version differently than to the gene taken from monkeys. "Having determined the composition of this group, we got our hands on a set of tools that allow us to influence human speech at the molecular level," says Konopka.
This collection of genes is likely also involved in the evolution of speech and language, as many of its components control the development of the brain or are associated with cognitive abilities. Part of the genes determines the appearance and controls the movement of the tissues of the face and larynx (which are known to be actively involved in articulation).
Geschwind's preliminary studies of the evolution of those 116 genes showed that they had roughly the same history. “Perhaps they changed all together, as if in a bundle,” the scientist argues.
Daniel also notes that despite the proven importance of FOXP2, he wouldn't call it the "speech gene". Perhaps FOXP2 is only part of a certain group, or it is not the first link in the chain (its work is also controlled by some hitherto unknown substance), the biologist explains.
Geschwind says this for a reason. His group conducted a second experiment: they compared gene activation in adult human and chimpanzee brain tissue. It turned out that there is an overlap in the work of those genes whose activity differed in the human brain, and those that were controlled differently by the human version of FOXP2.
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It is too early to draw any conclusions, but it is likely that most of the differences in the brain Homo sapiens and chimpanzee (along the language line) is due to only two small changes in one gene. "If that's true, it would be incredible," says Wolfgang Enard of the Max Planck Institute for Evolutionary Anthropology. (On our own, we add that this again emphasizes the smooth transition of abilities from chimpanzee to man.)
"This work is the starting point, the basis of all future molecular research dedicated to the study of the evolution of language," adds Yale neuroscientist Paško Rakić.
Commented on the current work and Professor Faraneh Vargha-Khadem (Faraneh Vargha-Khadem) from University College London. She deals with speech disorders of patients due to genetic abnormalities (and in the activity of FOXP2 in particular).
The professor agrees with the conclusions of the current scientific group and notes that her patients often have a curved shape of the lower part of the face (which again confirms that the influence of FOXP2 is multifaceted). Perhaps chimpanzees cannot speak due to the same physical disabilities. Man could not dance if he did not have legs, compares Vargha-Khadem.
Yes, none of our smaller brothers, including chimpanzees so close to us, can communicate as meaningfully and fully, but at the same time, horses, for example, use some kind of words, monkeys seem to understand grammar and distinguish voices, and meerkats - the intonations of relatives . Maybe they would put their thoughts into words, but they do not have the appropriate genetic prerequisites.
Faraneh also supports Daniel in the issue of an integrated approach to the development of speech in humans. You should not concentrate on just one gene and its many wards, she says.
In addition, Vargha-Khadem suggests that FOXP2 only gave a person the physical ability to speak, but this does not explain how abstract ideas materialized in ancient human brain into words, how higher cognitive skills appeared. And this is yet to be dealt with.
However, scientists will still have to work with pronunciation for a very long time. After all, if you think about it, “the movement of all those muscles that are responsible for pronunciation is also a small miracle,” says Vargha-Khadem. In order to reproduce sequences of sounds in such a way that they are understandable to the listener, one must also go through a very long way of development.
So far, no special, incredible advantages have been found in humans. Maybe some animals are already moving along this path, gradually and imperceptibly catching up with people?
Speech is a brain function that is unique to humans. But did the Neanderthal possess it? The latest "readings" of the amino acid sequence of the protein product of the speech gene suggest that, at least, the inhabitants of the Neander River Valley, a tributary of the Rhine, did not have developed speech.
It all started more than 10 years ago, when the KE family was described in England, three generations of whose representatives suffer from speech and language disorders in the more general sense of the word. Not only did they say "Koikogo Street", they also changed the order of words in a sentence, which is simply unacceptable in English. At the same time, their level of intelligence as a whole did not particularly suffer.
Chromosomal studies of family members made it possible to identify the zone in which the defective gene was supposedly located. The researcher who first described the KE family also described a 5-year-old boy with similar speech impairments. Chromosome analysis revealed a translocation (i.e. "jump") of a section of the 5th chromosome to the 7th, as a result of which one of the genes simply "broke" in half.
The gene was named "Speech", which means "speech" in English. It codes for a protein that is an important regulator of gene activity. Damage to the gene leads to a point replacement of arginine with histidine in the primary structure of the protein.
Journal article Nature, devoted to the description of the speech gene, was published in October 2001. And in mid-August 2002, the journal again turned to this topic by publishing an article by S. Paabo from the Leipzig Institute for Evolutionary Anthropology.
At one time, Paabo became famous for isolating and sequencing mummy DNA. This time, he sequenced speech gene proteins in great apes, humans, and rhesus monkeys. Ancestors of apes and macaques diverged from each other about 70 million years ago. Mathematical analysis amino acid sequences showed that the human version of the speech gene was fixed 120 thousand years ago and not earlier than 200 thousand years ago.
What were the benefits of the human form of the gene? It is quite possible that it was the development of speech communication as the most information-intensive and requiring a minimum of energy that became the advantage that allowed modern man"cope" with their Neanderthal brothers.
Based on materials
Nature, 2001, No. 6855, p. 519
Science, 2002, No. 5540, p. 32; No. 5584, p. 1105
Despite the various tricks that laboratory mice can do, scientists are still trying to expand the arsenal of tricks of their wards. Super-hardy, super-strong, super-fast, super-resistant or, on the contrary, super-susceptible to the most dangerous diseases - the list of abilities genetically acquired by the will of scientists is not limited to this.
Wolfgang Enard of the Max Planck Institute for Evolutionary Anthropology in Leipzig and his colleagues set themselves the almost impossible task of teaching mice to speak.
Well, or at least transplant the human version of the Foxp2 speech gene into mice.
Mice, and other animals, including primates, also have this gene, or rather, the DNA sequence encoding the Foxp2 transcription factor, but it differs from the human one by two point mutations. It is believed that these mutations gave a person a unique ability to both speak and distinguish speech. In estimates of the age of this mutation, scientists disagree - from 100 to 500 thousand years. The question of the age and evolution of Foxp2 has even become almost the main topic in the discussion recently decoded Neanderthal genome.
However, the effects of this transcription factor remain unclear. Obviously, such a complex process as speech cannot be provided by just one gene; an appropriate structure of the respiratory tract and vocal cords is necessary. In addition, the brain and the organ of hearing must be able to perceive and distinguish this very speech. Foxp2 is the best fit for the role of a "regulator" - after all, it is a transcription factor that regulates the work of a wide variety of genes (which ones are not completely known). That is, one mutation in the Foxp2 gene is enough to change the structure, properties and functions simultaneously in several tissues - whether it be the nervous or respiratory system.
Foxp2 has become a "speech gene" relatively recently: at the end of the last century, it turned out that its mutations are the cause of congenital defects in speech perception.
But the mechanism of action, as well as all the functions of this factor, remained unknown until today. Looking ahead, Enard's work left many questions, even though scientists were able to describe the effects of the human version of Foxp2 in mice. Authors publications in Cell, the list of which, together with the institutes, took up the entire first page of the article, tried to answer two questions at once: what is the role of Foxp2 in general and what is the difference between the effects of human and mouse Foxp2.
To do this, they first had to breed mice heterozygous for this gene - Foxp2 wt / ko (wild type / knockout), that is, one version of this gene was "wild" - mouse, and the second - completely turned off. In addition to this group, the scientists also obtained Foxp2 hum/hum (human) mice, which had the human version of the gene in both positions. After that, Enard and colleagues, among whom was the “chief specialist” on the Neanderthal genome, Svante Peebo, evaluated the mice according to almost three hundred physiological criteria.
The "humanized" mice never learned to speak, and even had less dopamine secretion and lesser exploratory enthusiasm, but produced quantitatively different ultrasounds.
The absence of one copy of the gene led to an absolutely opposite effect, which once again proves the role of the human version of Foxp2 in all observed phenomena. The reason for these differences is in the basal nuclei of the telencephalon. It is here that the redirection of signals from the cortex occurs. hemispheres to the muscles, and many reflexes “close” here. The decrease in activity in the search for and study of new objects is explained by a low level of dopamine, a mediator of pleasure that stimulates such behavior.
As for the main topic for discussion - the effect on speech, here most of the differences turned out to be insignificant, although the authors were able to find a small difference:
"humanized" mice were more likely to emit more individual sounds and used for this lower peak frequencies compared to knockout frequencies for one of the genes.
However, this only demonstrates the role of a particular human version, and not Foxp2 as a whole.
Apparently, Foxp2 has the greatest impact on speech and sound recognition, as well as on the central regulation of speech. The most interesting thing, mice that did not learn to speak during their lifetime, were told to scientists after dissection:
in "humanized" mice, the average length of short processes nerve cells- dendrites - turned out to be 22% more.
It promotes education more contacts between cells, and therefore more effective work nervous system and, in particular, the auditory analyzer.
Thus, Enard once again confirmed the fact that evolution within such a perfect group as animals was mainly due to transcription factors, and not genes in the usual sense of the word. It remains to look for Foxp2 in parrots, and the question of its role will be finally resolved.
The speech gene helps to move from one stage of learning, in which understanding and understanding of the task occurs, to another, when the desired skill is learned to an automatic state.
Speech abilities are provided by the work of a special neural apparatus, and the structure of neural networks depends on genes, so it would be absolutely correct to assume that we have special “speech genes”. However, until 2001, scientists knew almost nothing about which genes affect speech. The situation changed after the study of one family whose members suffered from speech defects, and they had problems not only with pronunciation, but also with syntax, and with understanding someone else's speech. It turned out that in this family the gene is mutated FOXP2, who instantly became a "star" in the scientific world.
Our ability to speak is due to several mutations in the speech gene. (Photo by H. ARMSTRONG ROBERTS / Corbis).
Striatum in the human brain. (Photo Wikipedia).
It soon became clear that he was responsible not only for the intelligibility of speech: apparently, a person generally learned to speak with the help of FOXP2. It, of course, was also found in chimpanzees, but in them it differed from the human one in two nucleotide “letters” in DNA; it is likely that mutations helped turn animal sounds into highly structured speech. In 2009, a curious experiment was carried out: the human FOXP2 were introduced into the genome of mice, after which the latter, of course, did not begin to speak in a human voice, but the sounds they made became noticeably more complicated. Further studies showed that mice with human genome speech, the activity of neurons in the striatum (or striatum) changed, which, among other things, is involved in learning processes. Moreover, even the notorious female talkativeness was linked to this gene - after it turned out that the level of protein FOXP2 girls are almost a third higher than boys. However, the details of how this gene helps us learn language remained largely unclear.
We and animals learn in two stages. At the first, the task is divided into several steps, which we gradually learn to perform. In the case of, for example, cycling, we pick up the steering wheel (and try to keep it level), then we put our feet on the pedals, and then we start to rotate them. At first, this sequence of actions requires our full concentration, but over time, the "unconscious" part of learning begins, when we learn to drive better and better, simply by repeating all the above actions. The same thing happens with language learning: first we concentrate on pronunciation and meaning individual words, then speech becomes more and more fluent, and, in the end, we can say “good afternoon” on the machine, without thinking about how and what we say.
Researchers from (USA) decided to find out which of the stages of learning needs a speech gene FOXP2. In the experiment, normal mice and mice with the human gene had to find their way through a maze to get a treat. The “humanized” animals were quicker to understand which route would be faster to get to food, however, when the maze was organized so that the stages of learning could be separated and observed separately from each other, there was no difference between the mice.
Then a hypothesis arose that the speech gene helps to switch between different phases of learning. Further experiments, described in an article in the Proceedings of the National Academy of Sciences, confirmed this assumption: mice that mastered the step-by-step task stage switched to the repetition learning phase faster if human FOXP2 was introduced into their genome. The effect could also be seen at the cellular level: in the striatum, different zones are responsible for different stages of learning, and the one that was responsible for learning by repetition was activated more efficiently in mice with the human gene.
That is, we can say that the human version of the gene FOXP2(which is believed to have arisen about 200 thousand years ago) revealed to our ancestors learning by repetition - a person could not only pronounce a word and understand its meaning, but the reproduction of this word became automatic. The increased possibilities of communication in the collective helped separate individuals to survive, so that a new version gene has an evolutionary advantage. However, it is unlikely that the development of speech in humans occurred “by the will” of only one gene. Obviously, a whole genetic network is involved here, in which FOXP2 is just one of the links. So, a year ago, researchers from the Johns Hopkins University School of Medicine (USA) published an article in which they described dependent on FOXP2 gene SRPX2, which controls the dynamics of interneuronal connections in the speech center of the brain. It should also be noted that in the described experiments with the gene FOXP2 the ability of mice to learn in general was evaluated, so it is likely that this gene in humans may be related not only to speech abilities.
