Summary: The Affects Of Genetic Influence On Intelligence

Most scientists agree that genes have some influence over general intelligence and special aptitudes in such activities as athletics, mathematics, music, and science. But genes are not the only factor involved in producing these characteristics.

The brain is one of the most complex, unknown organs of the human body. Researchers often break down the characteristics of the brain to whether tendencies are achieved through nurtured environments or the inheritability of genetics. Intelligence is one of the most controversial topics when it comes to deciding whether environment or genetics are most influential. Many argue that intelligence is based on environmental factors and the unique ability to work hard, but fail to realize the essential cognitive qualities concerning what truly defines intelligence. Although some may consider this trait as based on environment, intelligence is a cognitive attribute established by the nature of genetics.

Almost all individuals have a unique genotype. This affects their aptitudes and intelligence. Certain children have noticeable cognition deflects that limit their ability to learn. Some of the conditions that lead to such deficits are strongly influences by genetics.

Human behavior is a loosely defined foundation for individuality, generally considered to be influenced and developed by the environment. However, recent molecular studies have exposed genetic factors that suggest a more biological origin for behavior. Gene segments in the genome of humans and other animals have been identified and associated with particular behavioral traits. Is it possible that the presence or absence of even a single gene may predispose one to alcoholism, increased irritability, or enhanced intelligence? Clearly exploration of the nature versus nurture argument with regard to genetic predisposition has social, political, and legal significance.

Charles Spearman’s theory (1904) also takes the psychometric approach that there is a general intelligence. Spearman maintains that intelligence is hereditary and an individual is born with their maximum mental ability. This suggests that intelligence cannot be changed or strengthened. The concept of ‘general intelligence’ suggests that an individual has an underlying intelligence, in which their performance in one type of cognitive task is often similar to their performance in another (Boundless 2013). Spearman demonstrated this through the correlations between tests, where individuals who performed well in one test, often performed well in others. This led Spearman to the conclusion that intelligence is defined as a single factor. However, critics refute Spearman’s conclusions, as they argue that one cannot reduce all factors of intelligence to an indefinable “g” (Neisser et al. 1996).

A twin study, conducted by the National Institutes of Health Public Access in 2007, shows that genes account for 32% to 45% of mathematical skill at a young age. Individual effort accounts for 55% to 68%. A twin study measures the variation in conduct in a large group and estimates how much of the change is due to genetics, shared environment, or unique

A study intending to emulate the results expressed in the original study was performed on preschool aged children exposing them to similar variables as those in the original study (Hui, 2007). The study showed no empirical evidence that listening to Mozart is more beneficial for children than ulterior conditions (Hui, 2007). This disproves the belief that listening to Mozart makes a child smarter also making the generalization from the Rauscher et al (1993) inconclusive. There are also a number of other factors that have been overlooked when comparing the finding of the original study to the Mozart effect in children. Another discerning factor expressed in the original study was the test used to assess intelligence between the participants. The portion of the Stanford-Binet test used in the original study focuses on one aspect of intelligence, namely, spatial reasoning (Rauscher et al, 1993). Therefore, it would be invalid to assume that high scores on this specific test delineate an increase in overall general intelligence. The test itself is also bias as specific cultures outperform others, as cultural environment has an influence on intelligence, which may lead to deficits in the results found (Weinberg, 1989). Sternberg (2004) found that IQ tests are effective at predicting academic success in western individuals but are not conclusive measures of overall intelligence or ability to succeed. Gardner (1999) also proposed that IQ test also

Another study to study SES and cognitive development was done by Merete Osler1, Kirsten Avlund, and Erik Lykke Mortensen to examine the influence of social circumstances early in life on changes in cognitive function from young adulthood to middle age (2012). They looked at the impact of birth characteristics like birth weight and maternal age, childhood activities in leisure time, education and adult social class on the expected relationship. A sample of 11 532 men aged 12, 18, and 57 were assessed. To find the association of early-life characteristics with cognitive test scores, a linear regression was used. They found that the scores at age 57 years highly correlated with the scores at ages 12 and 18 years. Participants who had a father in the working class at birth were related to having lower cognitive function at all three ages. It was also found that a decline in cognitive function was present with low education, many social activities and minimum intellectual activities during childhood in leisure time and low adult social class.

Identical twin studies are most useful in determining genetic influence on intelligence. Since the identical twins share the same exact genes, the straightforward comparison of intelligence can display if this human trait is truly heritable. Similarity of intelligence scores between identical twins supports the genetic influence on intelligence. According to Myers (2007),

The world of Genetics is one that is both fascinating and interesting. When tackling how genetics plays a role in behavior, one must look within the scope of what genetics is before dealing with how it plays a significant role in one’s behavior. Simply put, genetics is the study of genes. It is a biological component within the entire study of biology itself. Scientists who study genetics and perform research do so with the intent to learn more about how genetics affects the overall attitudes, behaviors and dispositions of individuals. It could be said that genetics is somewhat of a psychological-biological science as researchers look at the underlying patterns within the genes that cause

Once a person has an idea of what intelligence is and what it means, a final thought one might consider is what influences are responsible for the different types of intellect. Two possible influences are genetics and the environment in which one lives, with genetics being the strongest influence (Santrock, 2009, pg. 302). Most researchers agree that a person’s genetics and environment interact with one another to influence the outcome of that person’s intelligence (Santrock, 2009, pg. 302). Genetic influences should be pretty obvious, so there should be no need to explain it; a person’s environment on the other hand, can involve several factors. An environment can consist of elements such as a person’s school, home, friendships, family relationships, and workplaces. All of these components factor in to influence a person’s intelligence.

One of the most interesting and controversial areas in behavioral genetics, human intelligence is currently assumed to be subject to both genetic and environmental influences.

Debates on the relationship between birth order and intelligence have been remaining controversial. Birth order is considered as a person's ranking by age among his or her siblings. There have been numerous researchers studying about this subject to find whether firstborns generally have a higher IQ scores than their siblings. Some scientists conclude that birth order strongly influents intelligence; however, others oppose to this, claiming that birth order has no effect on intelligence. In this paper, my study deals with the birth order effects on intelligence.

Intelligence is used by everyone to help them in everyday life. Where people get their intelligence, however, is debatable. A person is born with an amount of inherited intelligence; this intelligence is considered nature, genetic, or heredity. Then there is intelligence that comes from the ability to learn from experience; this intelligence is impacted by nurture or the environment. It is known that both genetic and environmental factors determine intelligence, but the subject is controversial among professionals. Does nature or nurture have a bigger impact on intelligence? Is it true that some people are born with high intelligence, but are limited by their environment? Given the proper tools, can a person increase their intelligence? How accurate are IQ tests?

Furthermore, studies have found there is a genetic link to verbal abilities (which is also correlated with verbal intelligence). In one study it was concluded that the genetic influences on verbal intelligence become more significant over one’s lifetime in explaining differences between individuals, whereas environmental factors decrease (Hoekstra, Bartels, van Leeuwen, Boomsma, 2009). Additionally, twin and adoption studies on verbal memory and fluency in early childhood (as well as adulthood) show that there are “moderate to strong” genetic influences (Hoekstra, Bartels, van Leeuwen, Boomsma, 2009).