"Twins have a special claim upon our attention; it is, that their history affords means of distinguishing between the effects of tendencies received at birth, and those that were imposed by the special circumstances of their after lives." says Sir Francis Galton, 19th century behavioral genetics pioneer. Researchers have used twin studies to try to figure out the genetic backgrounds of an abundance of traits, from determination to intelligence to bizarre to alcohol dependence.
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.
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
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.
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 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.
Parallel to this, the focus on genetics is Particularly convicted in twin studies, which establish a comparison between monozygotic twins that are identical and dizygotic twins, which are opposingly non-identical. This distinction can be identified in Torgersens study, which compared MZ and same sex DZ twins where one proband had an anxiety disorder, and it was discovered that such disorders were 5x more frequent in MZ twin pairs, who mutually shared identical genetics.
For major depression between monozygotic and dizygotic twins suggest a heritability of about 37%. It is lower than the heritability of bipolar disorder or schizophrenias.
Conjoined twins are a rare phenomenon. In the even that a set should appear where one twin is dependant upon the other, I believe that they should be separated, at minimum, to save the life of one. At the same time, I believe that every set of conjoined twins is its own special case. In this study, I will present the background information on conjoined twinning, give a few case studies, and give the pros and cons of conjoined twin separation. I will end with my own views on the subject.
According to Begley, identical twins are not always identical in behavior just because of genes. Some studies show that when twins are given different circumstances, for example, different educational opportunities, different results are obtained. One example in Newsweek showed one twin may grow to be a professional pianist while the other twin was not at all musical even though the twins were both raised in a musical environment ("Heredity" 69). Twins have different interest from each other, and express them in individual ways.
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
In reading stories about identical twins my point of view is easily understood. Various types of psychologist have analyzed the study of identical twins. It shows that individuals with the same genetic make-up can be totally different, when it comes to personality. Nurture promotes the twins to grow up as separate individuals. Its a lot better if a twin has his or her own personality rather than the same exact personality of the other half. I think this great debate weighs heavier on the nurture side. As a child my parents, and sibling overshadowed my genetic make-up. No matter how much I thought my physical traits made me behave. It did not affect me more than the things that I had seen and been exposed to. The more things that I had seen around and experienced made me the person that I am today. If my genetic make-up was totally different, to a certain extent, I am sure that I?d behave the same way that I do presently. There are exceptions to that. For instance if I were six foot five and one hundred and ninety pounds, I?d most likely be in the NBA and be really rich. I think if I was really rich and in the NBA I wouldn?t have the same worries that I have today. Even if before I were in the NBA I would have lots of attention and have a lot more confidence. So to an extent I would change a little if my genetic make-up were different. In a sense, genetic make-up is just a competitor to the environmental factors
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),
As I walk through the crowded mall with my sister, little children stare, most adults do a discreet double take, and some bold adults question us outright. “Wow, are you twins?” “Do you know you look the same?” “What’s it like to be a twin?” “Do you have, like, psychic powers, or something with each other?” These are the most common questions twins hear. Almost all twins don’t really mind them and sometimes the attention is cool. Mostly, we just smile tolerantly at each other and answer them as best we can. After all, we don’t really know how to describe being a twin. We have never known anything else. Nonetheless, here we are. So, as a person who might not know exactly what she is talking
There are many stories of identical twins who were adopted at birth who meet up late in life and discover they share remarkably similar life stories. A study in 1990 found that genetics account for 50 percent of how religious a twin was likely to be. There is also a genetic influence on dental or gum health. Among identical twins, most reported feeling closer and more familiar with their twin than they did to their best friends, even after just meeting them after spending so many years apart.
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
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.