Critically Review Evidence Genetic Environmental Influences Intelligence

Genetic and Environmental Influences to Intelligence
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Human intelligence has remained one of the most examined human behavioral traits. It has influenced investigation in numerous fields not just in the behavioral sciences but also in economics, genetics, and neuroscience. Human cognition represents a variety of higher mental functions like attention, perception, and memory (Gain, 2018, p. 4). Over the past decades, large data sets have been taken from twins and family members for the study of the genetic and environmental etiology for the variances in cognitive ability. More recently, the improvements in genotyping and DNA sequencing have facilitated the particular genetic variants essential for intelligence to the examined (Lowe and Reddy, 2015, p. 1432). The influence of genetics and environment on intelligence has remained one of the most controversial subjects. The assumption that genetics and environment influence human intelligence is held a majority of scientists although there is a disagreement on the degree of influence each contributes. Whereas the arguments for genetic influences are convincing, there is also growing evidence that the impact of the environment is significant and substantial. The purpose of this paper is to critically examine the influence of both genetics and environment on human intelligence.
There has been a shift in behavioral sciences that has led to a balanced view that recognizes the critical role of both nature and nurture in the development of individual differences in behavior. Genetic research has established genetic influence while behavioral genetic research has provided evidence of the importance of environmental influences on intelligence. The quality of human brain development is not just dependent on genetic endowment but also on environmental factors. Both genetics and environment may exercise their influences using a number of possible methods. Firstly, both genetic and environmental aspects may apply an unceasing influence since the time of inception (Tucker‐Drob, 2012, p. 252). The method indicates that the same genetic and environmental variables account for stability, probably with factors dependent on age. Secondly, both elements may be specified at a given age and affect cognition at that age only. Variation in mental growth may be because of age-related reasons. Finally, there could be a simplex-like connection in the effects of the two factors. Here, the effects are specific to a particular age, and there could be transition effects from one age to the successive age. Influences from earlier occasions may be transmitted to the next occasions.
Evidence of both genetic and environmental stimuluses on intelligence exists. Regarding the impact of genetics on cognitive ability, twin studies have demonstrated that identical twins Intelligence-Quotients (IQ) are more similar compared to those of fraternal twins (Oommen, 2015, p. 1). Additionally, siblings who have grown up together in the same home have IQ’s that more alike than those of adopted children who have grown in the same household. About environmental influences of intelligence, evidence shows that identical twins who have grown up apart have IQ’s that are less similar compared to the identical twins who have grown up in the same environment (Oommen, 2015, p. 2). Hence, the variability in cognitive abilities among various individuals can be ascribed to the interaction of both genetic and environmental factors. Whereas genetics account for about 50%, environmental influences account for about 20% of the variations in cognitive abilities. The environment can alter the genetically determined intelligence and an enriched environment can increase performance.
It is essential to note that the role of genetics and environment in intelligence changes during the lifetime of individuals. Studies agree that the influence of genetics increases with age, from childhood to early adulthood (Haworth et al., 2010, p 1113). Genes account for 60-80% of the variability of intelligence among adults (Plomin and Spinath, 2004, p. 114). The increase in the heritability of IQ with age can be attributed to genes that incline individuals to gain intelligence through particular environmental factors. Individuals with high IQ genotypes select stimulating environments and eventually attain a high IQ. In children, the brain is still developing and growing hence environmental factors like mental stimulation and nutrition can affect the development of the brain (Prado, 2014, p. 271). However, when individuals reach adulthood, the mind reaches the peak such that environmental factors have little effect on its development.
The structure and functionality of the brain play a critical role in determining the level of intelligence (Yoon et al., 2017, p. 11). The size and shape of the frontal lobes, the quantity of blood flowing to the lobes and the amount of gray matter in the brain are essential in determining intelligence. Where the pathways function appropriately, the brain becomes capable of processing information more efficiently, which in turn results into better IQ scores (Luders, Narr, Thompson and Toga, 2009, p. 159). Hence, despite genetic predispositions of an individual, the level of brain development is essential in determining cognitive abilities. Individuals who have genes for high intelligence will still have low intelligence if the brain is underdeveloped due to environmental factors. Further, genes direct the production of ribonucleic acid (RNA) molecules which determines how brain cells will grow and function (Pereira, 2017, p. 99). Hence, RNA molecules assist in the production of brain cells which are responsible for intelligence.
Although biology sets a certain level of intelligence because of brain volume, structure and pathways, how much individuals attain is not based entirely on biology. The king of lifestyles people live affects intelligence. According to Oommen (2014, p. 3), understanding the role of environment necessitates researchers to examine twins who have been separated from birth. They hypothesize that if intelligence is due to biological factors along, then identical twins who have been separated since birth should still possess the same IQs. However, scientists always find that identical twins have different IQs. Genetic influences can cause bright children to look for stimulating settings which increase intelligence. Activities aimed at increasing IQ would increase the cognitive ability of children as long as they persist in seeking out those demanding experiences. Further, nutrition has been associated with improvements in IQ. Evidence suggests that providing a high-nutrition diet to premature babies can minimize the loss of brain size and IQ which is prevalent among these children (Koletzko, 2015, p. 4). Intake of diet with Zinc, iodine and B12 deficiency among babies has also been associated with reduced intelligence (Harika et al., 2017, p. 1099). Hence, improved nutrition among children leads to optimal brain development. The nutrients offer building blocks that play an essential role in the proliferation of cells, the synthesis of DNA and neurotransmitter metabolism which enhances mental function.
A way of looking at the heritability of mental ability is considering the transactional framework. According to Tucker-Drob, Briley and Harden (2013, p. 349), children choose and induce experiences depending on their genetic tendencies. The experiences then arouse their mental growth. The compounding processes become more accelerated as the children grow and attain more autonomy in selecting who to associate with, and the courses to take. Progressive escalation in heritability is demonstrated in the genes that were not present during the initial influence of cognition, then they are later initiated during the development process. For instance, biologic...