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Updated January 22, 2021

The Role of Genetics in Determining Intelligence

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The Role of Genetics in Determining Intelligence essay
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Abstract

Intelligence is basically a skill for cognitive problem-solving. It is the mental ability to reason, recognize relationships and analogies, calculate, learn and comprehend things etc. In simple words, ‘Intelligence is what you do when you don’t know what to do’ (WWW3). Certain psychologists have broken down intelligence into 7 components: musical, bodily-kinesthetic, logical-mathematical, linguistic, spatial, interpersonal and intrapersonal (WWW3). Certain studies reveal that genetics influences in determining intelligence and in this paper I will be focusing on those studies.

I found this article interesting because I have seen a lot of cases where if either of the parent is a doctor at least one of their children will become a doctor and this makes me wonder if genetics really is superior to environment in determining intelligence. Before coming across these articles I used to believe environment was superior. In the reference articles, the authors have done research and experimented how genetics plays a role in determining intelligence. (Smajlagić et al., 2018) spoke about their research in which a few participants were recruited; their intelligence was measured by the Wechsler Intelligence Scale for Children (WISC) and genotyping was performed on them, followed by imputation. (Hill et al., 2018) has done a study whose aim was to merge two large genome-wide association studies of education and intelligence and by doing this their functional sample size increased.

The outcome of their study was that 187 independent loci were associated with intelligence, suggesting 538 genes. (Hill et al., 2018) argued that they found evidence which would prove that neurogenesis and myelination may explain a few biological differences in intelligence. However, these articles have limitations and unanswered questions. In these articles only one or two type of genes are studied and tested and based on the results it is said that genetics influences intelligence whereas according to (WWW2) the genetics of intelligence is not controlled by a single intelligence gene instead it is a result of many complicated interactions between many genes.

Introduction

Intelligence is the ability to perceive information and use it as knowledge. It is one of the most important resources of a human being. There is a very famous quote ‘Knowledge is power’ (Francis Bacon). People like Albert Einstein, Stephen Hawking, and Newton are very intelligent and smart because they used their intelligence to comprehend things or information and use it as knowledge in their respective fields. I found this article interesting because I have seen a lot of cases where if either of the parent is a doctor at least one of their children will become a doctor. I really wanted to become a doctor and the environment I grew up was an optimum one. My parents were very well educated; both of them are professors. I worked very hard to get an admission for MBBS course to become a doctor but unfortunately I couldn’t.

The country where I come from is very competitive and only intelligent students get a merit seat for the MBBS course. I have a few friends whose parents are doctors and now they are pursuing a career to become a doctor. All these experiences made me wonder how genetics can influence so much on determining intelligence and hence I chose this topic. (WWW2) stated that “Siblings reared together in the same home have IQ’s that are more similar than those of adopted children raised together in the same environment” and this is an example of how the genetics influences in intelligence. From the reference articles the subtopics I have chosen are genome-wide analyses in ALSPAC, role of neurogenesis and myelination in intelligence, and is most of your intelligence decided by your genes? And I think these topics will give a clear understanding as to how genetics influences intelligence.

Genome-wide Analyses in ALSPAC

The ALSPAC stands for Avon Longitudinal Study of Parents and Children. Smajlagić et al., main aim was to find out whether the method of delivery may constrain the genetic disposition of intelligence in children. In order to find out this they carried out a study in which they collected data from 14,009 participants and these were all taken from pregnancies. Moreover, these participants were followed for over 20 years to generate an enormous amount of data through questionnaires, measurements and biological samples. Furthermore, only 6832 children’s genotype data matched with Phenotype (2018). A total of 9912 participants’ DNA was extracted from blood or buccal swab samples and then it was prepared for genotyping. Additionally, to ensure that no individual had poor genotyping rates, the authors had done a quality control in software.

Furthermore, the measure of intelligence was divided into Verbal intelligence quotient (VIQ), Performance intelligence quotient (PIQ) and Full scale intelligence quotient (FSIQ). Firstly, 5 oral tests were used to measure VIQ: information, similarities, arithmetic, vocabulary, and comprehension. Secondly, the PIQ was measured based on 5 non-verbal problems: picture completion, coding, picture arrangement, block design, and object assembly. Lastly, the PIQ and VIQ were used to determine the FSIQ (Smajlagić et al., 2018). The genome-wide interaction analyses was carried out by performing linear regression analyses in which first a model is constructed with outcome as each of the IQ measurements thus checking the effects of SNPs, mode of delivery and sex. Furthermore, a total of 2,141,747 SNPs and 2,421 individuals cleared all quality control filters and also they had all phenotypes available for analyses (Smajlagić et al., 2018). The figure below outlines the phenotypes examined, the number of participants, and the sex distribution by each IQ measure.

There was no effect of genome-wide at any SNP and also not a single genome-wide finding for any of the intelligence measure in the models was revealed by their analyses. Furthermore, the authors concluded their study by stating that they observed a few potentially relevant loci that showed a moderate effect of delivery mode on childhood intelligence. Lastly, the other finding was that a gene known as GRINA2A gene encoded a subunit of a protein family member which plays an important role in the nervous system (Smajlagić et al., 2018).

Role of Neurogenesis and Myelination in Intelligence

To understand the role, two large genome-wide association studies (GWAS) of education and intelligence were merged in this study and by doing this the functional sample size had increased. There are two strategies to maximize the power by increasing the sample size for loci discovery in intelligence research: the first strategy is by meta-analysis of GWASs performed on intelligence but this method has limitations as each individual sample use different cognitive tests and these samples are small, thus the meta-analysis is underpowered. The second method is by using a proxy phenotype showing high phenotypic and genetic correlations with intelligence (Hill et al., 2018).

Hill et al., in their recent study, using MTAG combined the above two approaches and this resulted in the increase in sample size to GWASs of intelligence by adding the genetic variance. Moreover, all the genotyping procedure was carried out by UK biobank. Furthermore, these authors used the SNP-based and gene-based GWAS to maximize the ability to discover loci and genes related to intelligence and the next step was the use of functional mapping to identify and annotate genetic associations and finally they applied the gene-set analysis to extract biological meaning from their data (2018). The samples were selected by obtaining statistics from GWAS meta-analysis of intelligence and education and the genetic loci related to intelligence was identified by the following procedure: first, identification of independent SNPs were carried out and the these SNPs were selected on the ground of their P-value.

Secondly, the SNPs that were in LD were further included for further annotation. Thirdly, the identification of lead SNPs (the independent SNPs that were in LD) was done. Fourthly, by merging lead SNPs the genomic risk loci were determined. Lastly, all the SNPs that were in LD formed the border of the genomic risk loci. Lastly, the next step in the study was conducting analysis of gene-based using multi-marker analysis of genomic annotation (MAGMA) which was followed by gene-set analysis on 10,891 gene-sets to examine enrichment in intelligence (Hill et al., 2018). The outcome of study was that the sample size had increased from 199,242 to 248,482 and this was achieved by combining datasets using MTAG.

Furthermore, the next finding was that using both SNP-based and gene-based GWAS, 187 independent loci was found to be in accomplice with intelligence affecting 538 genes. Lastly, the authors argued that by putting into account of all their findings they had enough evidence to conclude that neurogenesis and myelination along with the genes expressed in synapse, and those genes that were involved in the regulation of nervous system can explain a few biological differences in intelligence (Hill et al., 2018).

Is Most of Your Intelligence Decided by Your Genes?

To find out the answer let us analyse the (WWW1) study. In this study the author considered intelligence the same as other human traits like strength, weight and height. Moreover, to better understand this the author mentioned an experiment where he gave a scenario in which there are 5 plots of lands with different soil quality and in each of the plot of land 10 genetically different seeds were planted. However, the same 10 seeds were cloned and used for each plot of land (WWW1). There is a direct proportionality between the average heights of the plant for each plot to the quality of soil of that plot of land but, the internal variation of the height within one plot of land will be determined by genetics.

Besides, this same concept can be used for human population, people in different countries are planted in soil of different quality and this quality of environment where people grow up varies from country to country. Furthermore, the average differences between people will be determined by these variations (WWW1). One important fact that the author highlighted was that one country does not portray the same environment for all the inhabitants which means every country has different environments of different quality. For example if one class of people in a country were exposed to a poorer education, workplace, neighbourhood etc. then that will obviously create a low intelligence environment. To further understand this subtopic I came across an example in (WWW1). Say the scientists have discovered the genes for muscles to get stronger; a few people think the above statement means that there are genes which can promote the muscles to grow stronger than other people.

Furthermore, let us consider two twin kids rose in the same family, then it would mean that the kid with bigger muscles have muscle genes and this case would be true but not always. Moreover, this case has alternate explanations; one explanation would be that the kid having muscle genes have more passion in body building, hence by body building that person has bigger muscles. The alternate explanation would be that one of the kids recovers faster after lifting weights which enables him to work out more and the result being bigger muscles (WWW1). The last example I took from (WWW1) is of Norwegians. The author argued that the Norwegians are a great example where the raw talent is superior to a genetic advantage and this is due to the interaction with the environment. Additionally, one real life example the author gave was of the famous Norwegian skiers Marit Bjørgen and Therese Johaug and Johaug was not a talented skier in her youth whereas her sister was, but due to hard work of Johaug she won an Olympic gold medal whereas her sister couldn’t win (WWW1).

Conclusion

“Intelligence is what you do when you don’t know what to do” (WWW3). Genetics is usually considered as a factor in determining intelligence and this can be understood from the first two subtopics. (Smajlagić et al., 2018) discussed about how the participants were recruited, their intelligence being measured by the Wechsler Intelligence Scale for Children and genotyping performed on these participants. Furthermore, they claimed that they observed a few potentially relevant loci that showed a moderate effect of delivery mode on childhood intelligence. The authors (Hill et al., 2018) merged two large genome-wide association studies (GWAS) of education and intelligence and this was merged to increase the functional sample size and further they claimed that by taking into account of their research they had gathered enough evidence to prove that neurogenesis and myelination can explain a few biological differences in intelligence. (WWW1) considered intelligence the same as other human traits like strength, weight and height.

The author of (WWW1) believed that the environmental factors are superior to genetics in determining intelligence because the relative difference between numerous human populations has changed a lot through history. (de Manzano et al., 2018) claims that several studies suggested that intelligence and personality have a different effect on creative accomplishments in the arts and sciences and further states that there is also research which could prove that all these variables are influenced by both genetic and environmental factors. The limitation of these articles was that these articles focussed on only one or two type of genes and based on the results concluded that genetics influences intelligence whereas according to (WWW2) the genetics of intelligence is not controlled by a single intelligence gene instead it is a result of many complicated interactions between many genes.

The Role of Genetics in Determining Intelligence essay

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