Heritability: Monozygotic Twins Or Adopted Children

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).

Many psychologists agree that nurture play a greater part in the development of a human being. Studies such as those performed on monozygotic twins (identical), who share the same genetics and those performed

“Trying to separate out nature and nurture as explanations for behavior, as in classic genetic studies of twins and families, is now said to be both impossible and unproductive” (Levitt, 1). Social scientists have declared the nature-nurture debate to be unnecessary. Similarly, scientists feel that such debate is not only unhelpful, but also outdated. From geneticists’ perspective, nurture and nature interact to influence

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

The study of twins relies on studying teens raised in the same family environments. Identical twins (Monozygotic) share all of their genes, while fraternal (dizygotic) only share 50% of their genes. Researchers use this method to estimate the heritability of traits.

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 nature- nurture debate has many different case studies, which often questions environmental and hereditary aspects of the nature- nurture debate. A tangent which is focused on in this essay is how the case studies of schizophrenia and IQ, specifically affect twin and adoption studies. This essay will firstly, give a brief outline of the nature-nurture debate and the definitions of twin and adoption studies. Secondly, it will illustrate two main case studies, which are IQ and Schizophrenia studies. Thirdly, will contrast and compare the two and research’s impact on the case studies in regards to nature vs. nurture and finally, will conclude with the impact of the nature-nurture debate and twin and adoption studies.

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

Looking at the genetic role can pose a bit of a challenge. It isn’t plausible to remove outside influences and interactions from a child without risking irreparable damage to their development, and one cannot simply discount the socialization that has already occurred in an adult. So how do scientists solve these conflicting issues? By studying sets of identical twins separated at birth, children that have the same genetic makeup but were raised and socialized by different families in different

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 Minnesota twin study, Bouchard et al. (1990) was a longitudinal and cross cultural study to check the effect of heredity and environment on intelligence. This study was conducted on monozygotic and dizygotic twins separated from each other in infancy and reared apart. Approximately 50 hours of interviews and testing was done on each twin. For measuring intelligence, the WAIS test and the Raven test was used. The correlated IQ rates of the monozygotic twins reared apart were then compared to those that were reared together and dizygotic twins raised together to understand the result of heredity and environment on intelligence. This was useful as they shared similar genetic makeup but were exposed to different environmental conditions. Monozygotic

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)

This article starts off explaining five tests describing the validity of what they called the ‘equal environments assumption’ (EEA). The EEA is a bold concept that states how environmental factors do not contribute to the differences in twins, either monozygotic (MZ) or dizygotic (DZ), and traits in the twins are only different because of their genes, not the environment. It explains five tests that have been done to analyze the legitimacy of this theory, all showing evidence to support it. Another test was conducted as well, on younger children, and it found that even if some young twins had more contact than others, it had no effect on how they behaved.

Behavioral genetics is a branch of the study that researches and quantifies the effect of genes on humans. To conduct this research and determine what makes people uniquely different from one another twin and adoption studies are utilized. Twin studies consist of either monozygotic or dizygotic twins to evaluate the effects of hereditary on human development and behavior. Monozygotic otherwise called identical twins are developed form one sperm that fertilizes one egg, essential from one zygote that splits into two embryos and share 100% of their genetic makeup. Dizygotic are two sperms that fertilize two eggs and are fraternal twins that share up to 50% of their DNA (Belsky, 2013). To determine inheritability behavioral geneticists statistically

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?"