Investigating the Genetics of Language Acquisition

Author: Nathan Min

Edit: James L.

Abstract

A variety of genes play a major role in language learning and development. In this article, we hope to examine some of these genes and evaluate the extent to which language acquisition abilities are hereditary. To do this, we will first review the biological and neurological basis of language, as well as certain genes that play a role in language learning. We will then consider evidence suggesting the heredity of language. Finally, we will investigate whether certain genetic groups may be able to learn foreign languages easier due to their genotype.

Key Words: Second Language Acquisition (SLA)

Introduction

Second Language Acquisition: Nature or Nurture?

Despite the seeming omnipresence of Spanish classes in American high schools, surprisingly few Americans study or retain knowledge of foreign languages. In fact, a 2019 Washington Times article reported that while around 56% of Europeans are multilingual, according to the US Census Bureau, only 20% of Americans are multilingual [1]. The comparison between the United States and Europe is only one example of the global variation in bilingualism. While many factors, such as the environment one was raised in and one’s native language, play an important role in the ability to acquire a second language, a perhaps sometimes overlooked factor lies in genetics. In this report, we hope to investigate to what degree the ease of learning a second language is influenced by genetics. We shall begin with reviewing the biological and neurological basis of language.

The Neurological and Biological Basis of Language

Language is extremely complex. However, we can attempt to understand how human language works through reviewing the important areas of the brain in language acquisition and development. Wernicke’s area, located in the posterior superior temporal lobe, manages the understanding and comprehension of language, both through listening to speech and reading writing [2]. Disorders in Wernicke’s area (Wernicke’s aphasia) leads to retaining abilities to produce grammatically-correct sentences of proper length however, these sentences have little to no meaning [2]. Meanwhile, Broca’s area, located in the left hemisphere, controls the production of language, both oral and written [2]. Disorders in Broca’s area (Broca’s aphasia) leads to poor, labored articulation and speech [2].

Lastly, located near the occipital and parietal lobes is the angular gyrus, which is responsible for connecting language to auditory, visual, and sensory meaning [2]. An example of this could perhaps be when one associates the word “red” with a certain color, the word “loud” with a certain type of sound, and the word “smooth” with a specific tactile sense.

Furthermore, a variety of genes play an important role in language process and acquisition in humans. Here, we plan to go over two of these genes: the FOXP2 gene and COMT gene. The FOXP2 gene, located on chromosome 7, codes for a transcription factor called forkhead box P2 [3]. FOXP2 is integral to brain development and synaptic plasticity, which is the ability of the brain to change and reform new connections, or synapses between neurons, over time [3]. Researchers have also found that the forkhead box P2 protein plays a vital role in the proper development and acquisition of language [3].

Meanwhile, the COMT gene, located on chromosome 22, codes for the catechol-o-methyltransferase protein [4]. This protein is important in breaking down catecholamines [5]. Catechol-o-methyltransferase operates primarily in the prefrontal cortex, where it regulates the levels of various neurotransmitters including dopamine and norepinephrine and plays a role in functions such as inhibitory control and short term memory [4].

There are two versions, one (membrane-bound COMT) which is present in the brain and a shorter version (soluble COMT) that is present in the blood, liver, and kidneys [4]. Such functions, particularly of the membrane-bound COMT enzyme, would clearly make the COMT gene an important candidate to study when exploring the genetics of learning a second language.

Investigating The Heredity Of Language And Its Applications

Suggestions for a Strong Genetic Influence on Language Acquisition

A multitude of studies have suggested that language development, and more specifically language acquisition. For instance, in a study conducted by researchers at Osaka University the participants, all monozygotic or dizygotic elderly twins, were asked to give a verb based on text they read silently [6]. Low-gamma event-desynchronization (ERDs) in frequency range 25-50 Hz were then used to indicate brain activity in the left frontal region (the area responsible for human language) [6]. While the researchers concluded that both environmental and hereditary factors play a role in language learning, it appeared the “genetic control of ERDs” was virtually identical even between twins that were separated, suggesting the strong influence of genetics in language development [6]. Because the twins that were separated were raised in different environments, and the influence of the genes over the ERDs remained the same, it is likely genetics (the shared genetic material between the twins) played an important role in both language comprehension (reading the text) and generation (producing a verb).

Similarly, a study in the United Kingdom, conducted by Philip S. Dale, Nicole Harlaar, Claire M.A. Haworth and Robert Plomin, revealed similar results in regard to SLA [7]. In this study, 604 pairs of twins were evaluated, using the UK National Curriculum (NC) criteria, in three areas of performance: L2 (second language) abilities at 14 years old, L1 (native language) abilities based on teacher ratings at 14 years old, and L1 abilities based on a direct test online at 12 years old [7]. Correlations between twin pairs calculated for each measure [7]. Note that some twin pairs were identical, monozygotic (MZ) twins, meaning they shared 100% of genetic material [7]. Others were fraternal, dizygotic (DZ) twins, meaning they shared 50% of genetic material [7]. The study assumed that if correlations between MZ twins were larger than DZ twins, genetics played a larger role in second language acquisition than environment [7].

For our purposes, we will focus on SLA only. The results of the study pointed towards a genetic influence on SLA [7]. The MZ correlation for the L2 NC was .78 (.72, .82; 231), while the DZ was .48 (.40, .55; 373) [7]. The three numbers in the parentheses represent the low and high ranges of the 95% confidence interval, and the number of pairs included, respectively [7]. Overall, the heritability value for second language acquisition was 0.67 (.52, .80), far above that of shared environmental influence value 0.13 (.01, .27) [7].

It is clear, then, that heredity plays an important part in language. If heredity was strong in language acquisition, we would indeed expect the correlation for MZ twins, which share more genetic material, to be higher than the correlation for DZ twins, which share less genetic material, and are thus less “genetically bound.” A statistical analysis approach would reveal a p-value of 0.05 with a confidence interval of 95% [8, 9]. Because the intervals between the MZ correlation and DZ correlation and the heritability value and shared environmental influence value do not overlap, the results are likely statistically significant.

We have now seen that genetics plays a strong role in language development and acquisition. We will now investigate the effects of certain genetic conditions on language acquisition.

Effects of Certain Genetic Conditions on Language Acquisition

In a study by Ping C. Mamiya, Todd L. Richards, Bradley P. Coe, Evan E. Eichler, and Patricia K. Kuhl conducted on Chinese students learning English at the University of Washington, participants were enrolled in a language immersion program, and the white matter in their brains were analyzed throughout and after the program [5]. The study used specific DTI indices, namely fractional anisotropy (FA) and radial diffusivity (RD) values, as markers of brain activity and change due to language learning/development [5]. According to TA Keller and MA Just (2009) and D. Gebauer, et al. (2012), children with higher FA values and lower RD values were more proficient readers [5]. Diffusion tensor imaging (DTI) shows the state of the brain and white matter in response to foreign language acquisition [5]. The study found that COMT gene expression was correlated with FA and RD values in the superior longitudinal fasciculus, or SLF, during the immersion program [5]. The SLF is a bundle of fibers that connects the frontal lobe and ipsilateral hemisphere; it is part of the longitudinal association fiber system and plays a role in language [10]. Specifically, there are three variations of the COMT gene, as shown in Table 1 below.

Val/Val Amino acid valine is present in the protein coded for by both alleles of the gene.

Val/Met Amino acid valine is present in the protein coded for by one allele, while methionine is present in the protein coded for by the other allele.

Met/Met Amino acid methionine is present in the protein coded for by both alleles of the gene.

Source: https://www.pnas.org/doi/full/10.1073/pnas.1606602113

The study found that while the Val/Val and Val/Met groups saw a significant RD value decrease as the number of days spent in the immersion program increased, such a significant decrease did not occur in the Met/Met group [5]. In addition, the study found that FA values increased more markedly in the Val/Val and Val/Met groups than the Met/Met group during the immersion program [5]. In other words, the study found that increased COMT activity (in the Val/Val and Val/Met groups) led to better language acquisition (indicated by lower RD values and higher FA values) throughout the program [5]. The study further postulated that increased FA may be associated with increased brain myelination, more axonal branching and growth, among other effects [5]. Both of these effects in particular clearly have positive effects for language development (myelination, for example, helps optimize transport of information).

Besides COMT, a variety of other genes, many of which control dopamine receptors in the dopaminergic system, have also been implicated in language learning. Studies by Lane, et al. (2008) and Rybakowski, et al. (2005), for example, have found that the A-48G polymorphism (DbSNP# rs4532) of the DRD1 gene, associated with allele A, increases binding and thus strengthens executive function and inhibitory control [11]. Executive function is needed in understanding language, expressing language to communicate, and interacting socially with others, also known as pragmatic language [12]. Meanwhile, Klein, et al. (2007) and Jocham, et al. (2009) found that the A1 allele in the Taq1A polymorphism (DbSNP# rs1800497) leads to reduced probabilistic learning abilities due to impairing DRD2 receptor density and dopamine binding to the receptor it codes for [11]. Additionally, studies by Rodriguez-Jimenez, et al., (2006), Frank, et al. (2009), Frank, et al., (2007), M. Hirvonen, et al., (2004), and J. Hirvonen et al., (2005) have found that in the C957T polymorphism (DbSNP# rs6277) of the DRD2 gene, the T allele increases binding, leading to strengthening of reward learning and executive functions [11]. Clearly, as we have seen, the variations in various different genes have major implications for learning abilities, which would play a large role in SLA.

Some important definitions for the preceding paragraph are presented below for the reader’s convenience.

•Polymorphisms are defined as various forms or “versions” of a DNA sequence that appears in humans [13]. One person may have one specific polymorphism, while another person may have another [13].

•The “DbSNP#” refers to the ID of the polymorphism in the Single Nucleotide Polymorphism Database [14].

Lastly, we will also go over the effects of the FOXP2 gene on language learning. Interestingly, FOXP2 was previously thought by many to be the “grammar gene,” according to Pinker 1994; however, more recent studies have shown that it functions in vocal articulation rather than grammar, according to Corballis 2004 [15]. Furthermore, a more recent study by Peter et al. 2011 found that the FOXP2 gene is involved in non-word repetition, real word reading efficiency, and rapid oral reading, skills which would be integral for SLA and language development [15]. Corroborating this claim, another study has implicated a certain single nucleus polymorphism (variation) of the FOXP2 gene in congenital dyslexia (Wilke et al, 2012), suggesting that FOXP2 is required for normal language learning and development [15].

As we have seen through our various examples, genes play a heavy role in the proper development of language and SLA. However, we must make a caveat and also acknowledge the importance of environmental factors in language development. For example, the Critical Period Hypothesis states that there is a critical window of time in early childhood to develop a first language [16]. If this window is missed due to lack of social interaction and isolation, it will become very difficult for the child to learn human language “to a native proficiency” [16].

Potential Variance for Language Acquisition Abilities across Various Populations

Given that we established much of language learning is hereditary, it would also be natural to question whether language acquisition abilities differ between various ethnic and racial groups, given that various ethnic and racial groups have differing genetic traits. One study established the differences between various groups. This study, carried out by Meg A. Palmatier, A. Min Kang, and Kenneth K. Kidd, was conducted with a sample size of 1314 people, and utilized Polymerase Chain Reaction, the NlaIII restriction enzyme, and gel electrophoresis [17]. It found that low levels of expression of the COMT gene were most common in Europeans and were less common in other ethnicities [17]. This is in line with the results of previous studies, which found a proportion of people with the COMT variant with decreased expression varied across various ethnic groups, with 18-27% of Caucaians having the decreased expression COMT variant, 1.5% of Asians (Filipino and Chinese) with the decreased variant, 7% of Blacks with the decreased variant, and 28% of Saami (a Norwegian ethnic group) with the decreased variant [17].

Given that we found earlier the correlation of COMT activity and language learning/development, we could postulate that, at least with respect to COMT’s role in language development only, Caucasian people of European descent may struggle more with language acquisition than other races. However, such a proposition does not claim to be true, as many other factors would affect language development, and the statement was also an extreme generalization.

Language is the Culmination of Environmental and Hereditary Factors

In this report, we reviewed the neurological and biological basis of human language, as well as certain key genes that are important in human language. We then investigated whether language learning and development is genetic or environmental. Finally, we examined how variations in certain genes could affect language development and how this could vary between populations.

While genetics, as we have seen, plays a large role in language, we cannot ignore the environmental factors that affect one’s abilities to acquire a second language. For example, it is well-known that the difficulty in learning a new language depends on one’s native language. An English speaker would have much more difficulty learning Mandarin Chinese or Japanese than Spanish or French, merely due to the fact that these languages are vastly different from English and are not close relatives, while Spanish and French both share many cognates with English (which draws on many Latin word roots) and are both Indo-European languages along with English. Similarly, it would be more difficult for a Mandarin Chinese speaker to read English than Japanese, due to the heavier differences and lack of cognates.

We hope that further research into the fascinating genetics of language acquisition can aid in the personalized teaching of foreign language and language therapy for disabled individuals.

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