The Influences of Environment and Heredity on Measured 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.

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

One of the most enduring debates in the field of psychology is the controversial idea of nature vs. nurture. Throughout the endless history of the debate, no clear conclusion has been met, only hypotheses have been formed. At the center of the debate, human behaviors, ideas, and feelings are being determined, whether they are learned or inherited. Determining physical traits, such as eye color or hair color, are simple because they are hereditary traits. The idea of having a certain personality, intelligence, or ability is under discussion because scientists cannot determine if these traits are learned, or predetermined by genes.

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.

Twins, share a bond that no parent, child or sibling relationship can ever compare. There are two main types of twins, and these include: monozygotic (identical) twins and dizygotic (fraternal) twins, and they are compared by their emotional, behavioural, and cognitive similarities. (Robert Plomin, 1997). According to Social Issues Referencing, 2007, whereas Identical twins are formed from a single (mono) zygote and are genetic “carbon copies”, fraternal twins develop from two (di) separate zygotes, as a result of two eggs being fertilized by two sperms independently. (Social Issues Referencing, 2007, para. 8)

Twin studies are a vitally important tool for dissecting the nature versus nurture argument. Twins provide a naturally occurring experiment and they are most likely the best indicator of determining whether biology effects traits and psychopathology in human beings. Researchers are seeking circumstances involving twins providing evidence of known variations in the extent of genetic similarity or environmental stability. The key factor in utilizing twin studies to determine biological basis for personality differences exist among identical twins and fraternal twins. These studies provide data among the individuals that are genetically identical but yet, display visible differences that may be attributed to environmental differences. Additionally, researchers used such studies involving

The American Psychological Association studies have shown that environmental factors can contribute to an individual’s intelligence factor. Different revolution factors, natural selection factors, and environmental differences have an impact (Saletan 4). For example, a black kid living in a run down neighborhood may do worse than a white kid living in a rich neighborhood. Due to this, most children feed off of their peers, either at school or even at home. People in disadvantaged groups generally score lower on IQ tests than those who are not disadvantaged (Jackson 1). Different races have different advantages due to

One of the main purposes of the eugenics movement was to attempt to control the level of intelligence in the human race. This is not completely possible, however, as all genes are linked to other genes, and intelligence is affected by many more than just the one gene (Agar, 2006). In contrast to Galton’s theory, intelligence is not actually completely hereditary. Between 47 and 58% of intelligence lies in DNA, and the rest is based on environmental factors (Steen, 1996). Many types of intelligence tests have been created to measure the level of intelligence in humans. Defining intelligence in itself is a difficult task, as there are

intelligence is determined by environment or genetics. The fact that human DNA is nearly identical across

Nisbett, R. E. (2004) Heredity, environment, and race differences in IQ: A commentary on Rushton and Jensen. Retrieved October 12, 2016 from, PsycINFO Database.

The biological approach in psychology states that behaviour is determined by a genetic component which results in a particular trait or behaviour. A topic area within psychology where this can be investigated is the heritability of IQ, it is suggested that genetic influence is the only factor to consider when investigating IQ, however others have suggested that other factors may play a role in determining IQ.

Across studies of 10,000 twins, the intelligence test scores of identical twins reared together are virtually as similar as those of the same person taking the same test twice…Likewise, the test scores of identical twins reared separately are similar enough to lead twin researcher Thomas Bouchard (1996) to estimate that ‘about 70 percent’ of intelligence score variation ‘can be attributed to genetic variation. (p. 455)

While this assumption is accepted by a majority of geneticists and behavioral scientists, there is great disagreement on the degree of influence each contributes. Arguments for environmental influences are compelling; at the same time there is growing evidence that genetic influence on intelligence is significant and substantial (Eyesenck, 1998; Mackintosh, 1998; Plomin, 1994; Steen, 1996). The purpose of this paper is to explore the question: "How is intelligence influenced by heredity and environment?"

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.