Examining Genetic Influence On Intelligence

Identical twins are many times seen as genetic reproductions representing variations from twin to the other twin and are created because of environmental factors (Cervone & Pervin, 2010). Since identical twins share identical genetics, his or her personality seems to also share similarities. Moreover, the environment can impact fraternal twins, resulting in fraternal twins personalities and his or her characteristics similar to each other. For example, identical twins. Some research shows twins that are raised in the same residence have little differences from those who are raised in a different home.

Sibling studies theoretically control for social and environmental confounders, and monozygotic twin studies would be the ideal model for genetic and environmental control of potential risk factors for neurodevelopmental disorders. This type of studies supported the importance of genetic and social/environmental variables as risk factors for learning disabilities. Genetic vulnerability can be related to an increased risk for surgical disease (62, 71).

Table 3-1 examines the correlations between selected characteristics for the identical twins separated at birth and the twins raised together. When compared to each other, they both have very similar brain wave activity, blood pressure and heart rate in the physiological characteristics. The Raven intelligence test was very similar, but the WAIS IQ displayed a bit of difference when compared to the other comparisons made. Personality wise, they typically had similar personalities at the same rate as twins raised together. Psychological interests were off a little bit, but still very similar. The twins that were separated at birth had less similar psychological interests compared to the twins

Twin studies are a mainstay of the nature verse nurture debate because they allow researchers to conduct “natural experiments” on human beings. When researchers try to determine the relative importance of genetics and environment with regard to a certain condition, they have a hard time because they cannot generally get people with the same genes. This is where twin studies come in. Twins studies are part of the method used in behaviour genetics, which includes all data that are genetically informative. E.g. siblings, adoptees, pedigree data etc. Researchers use this method to estimate the heritability of traits and to quantify the effect of a person 's shared environment (family) and unique environment (the individual events that shape a life) on a trait.

The Minnesota Twin Registry started in 1983 and its goal was to establish a registry of all twins born in Minnesota from 1936 to 1955 to be used for psychological research.., T.J. Bouchard, working in conjunction with the University of Minnesota, started exploring the similarities and differences in characteristics like personality, career interests, and a variety of personal interests between identical twins who were reared apart. Research was conducted on twins from all over the world. The Minnesota Twin study gave scientists a new insight of the role of nature vs. nurture on human development and personality; it was the hope that twin studies would be able to tie genes to specific behaviors. From the study, we understand that twins who were separated at birth and raised in different families

Methods: The researchers needed a way to study a person who developed in a certain environment and how similar or different that person would be having been raised in a different environment. They came up with an experiment using monozygotic (identical) twins. Half of the pairs of twins were reared together (MZT); the other half were reared apart (MZA) and separated early in life. Each twin was individually given numerous surveys and

Intelligence by definition is “the ability to acquire and apply knowledge and skills” (Oxford Dictionary, 2014). However, many psychologists argue that there is no standard definition of ‘intelligence’, and there have been many different theories over time as psychologists try to find better ways to define this concept (Boundless 2013). While some believe in a single, general intelligence, others believe that intelligence involves multiple abilities and skills. Another largely debated concept is whether intelligence is genetically determined and fixed, or whether is it open to change, through learning and environmental influence. This is commonly known as the nature vs. nurture debate.

Using the information provided by Belmont and Marolla, Zajonc and Markus proposed the theory that as family size increases, the average intellectual climate of the family decreases. Zajonc and Markus put the data from the Belmont and Marolla study into a table that provided information about the number of children and the average intellectual score for the children. They noticed that in larger families there is somewhat of a leveling off or even an increase in scores for the extreme later-born children. The reason for this increase is because the other siblings start to leave the family and contribute towards the average intellectual climate. Zajonc and Markus also found that twins and triplets performed lower on tests of intelligence than non-twin siblings. Zajonc and Markus didn't try to claim that the only

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

In this study, they are used several type of method, one of the technique is used two or more test instrument to ensure the adequate coverage, for example the participants were given a battery of personality and mental ability tests, interest and value inventories and psychomotor tests. In addition, separate of examiners administer the IQ test, life history interview, psychiatric interview and sexual life history interview. The twin also complete questionnaire independently under the constant supervision of the staff members. Twin studies are valuable to researchers because identical twins share 100% of their genes and fraternal twins share, on average, 50% of their genes. Both identical and fraternal twins share certain aspects of their environment (e.g. religious practices in the home). This allows researchers to estimate the heritability of certain traits. Participants are asked about academic ability, personality, and interests; family and social relationships; mental and physical health; physiological measurements. Of interest to researchers are prevalence of psychopathology, substance

Another study that has been done was with separated twins. Each twin was raised in a completely different environment than the other. Genetically, they were both identical in every way, but the environment that they were raised in was very different. One twin was raised in a very hostile setting and slowly became violent as an adult while the other twin was

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.

There are many different variables one can look at in order to answer the question of how identical are the identical twins. In this study intelligence is selected as a variable to be analyzed. The study explores the impact of environment, genetics and sex on intelligence. What influences intelligence has been studied as part of health and development for a long period of time? This study provides with data on genetic factor and environment effect on development. Also it will help us understand how identical twins can or cannot be different regardless of their similar genetic makeup.

From these studies, researchers have found that twins who have grown up in the same household share similarities in the way they think, act, dress, speak, etcetera. However, with the first type of twin studies, researchers could not differentiate whether the similarities were due to them having identical/similar genetic makeups or growing up in the same environments. Therefore, in order for psychologists to know whether similarities in twins are genetic or socially influenced, they studied twins who grew up in completely different households and environments. The study showed that despite growing up with a different family and in a different environment, they still had noticeable similarities in fashion, interests, and thought processes (K.W. Brown, personal communication, August 29, 2017). Twin studies, as well as other studies, have greatly contributed to our understanding of overall role that genes play in the development of psychological traits and behavior.