Twin Studies

Twin studies are studies that involve both monozygotic (identical) and dizygotic (fraternal) twins. The purpose of these studies is to measure the contribution and the effect of genetics, as opposed to environment, to a particular trait. They allow the effects of nurture which is environment and nature (heredity) to be investigated. The classical twin study relies on studying twins who are raised in the same environment like in a family and compares the similarities between identical twins who share all of their genes, with fraternal twins sharing only 50% of their genetics for a trait. By examining how often certain traits occur in identical and fraternal twins, we are able to estimate how much genes affect these traits. Researchers assume that any likeness between monozygotic twins is due to genetics. However, the modern twin studies specialize more on the pairs of identical twins who are raised apart, and therefore they do not share the same environment. An example of the modern twin studies is a psychological study called The Minnesota Study of Twins Reared Apart (MISTRA) which began in 1979, at a time when people supposed that intelligence and personalities were only influenced by the environment. The basic design of MISTRA relied on finding identical twins reared apart and seeing what traits they had in common. MISTRA had used more than 81 pairs of twins from which most of them were often separated right after infancy. For instance, genetically identical twins Jim L. and Jim S. were reared apart since infancy and were first reunited at age 39. Researchers found many interesting similarities between them like: both of them had had a dog called Toy. Each of them bit his fingernails and had headaches. Both Jims were first married to a woman called Linda and then to Betty. Each had worked at a gas station, smoked cigarettes and liked the same brand of a beer. Jim L. and Jim S. had even similar voices, gestures and mannerisms. By using twin studies we can estimate how much the particular trait is affected by genes. These studies also allow us to study the influences of genes on medical studies. Even though the twin studies might have many benefits, there are several limitations as well. The major disadvantage is that there are only a certain number of twins which means that twin studies do not represent the whole society. Therefore, the generalizability of the results may be limited. In the classical twin study, one of the main limitations is that as the twins are raised in the same environment we cannot really predict the effects of nurture on certain traits. On the other hand, a disadvantage of the modern twin studies is that the twins who were reared apart had often different personalities which must had been due to growing up in the different household then. Along with twin studies, there are many ethical issues too. In many cases, in order to conduct a psychological study, researchers decided to separate newborn twins. Sometimes, these twins weren’t even told of having a twin! So is it right to take a baby away from its parents and its twin in the name of science?