Twin Studies Assumptions - Assignment Example

 Twin Studies Assumptions “A twin study is a kind of genetic study done to determine heritability”, explains Book Rags Com (2006). This kind of studies is based on the presumption that whereas identical twins, especially those raised apart, have identical genotype, the differences between them can be caused only by environmental factors. Examining the degree to which identical twins differ, the scientists try to find out how particular traits are influenced by genes and the environment. The greater similarity in identical twins than in non-identical twins indicates a shared genetic basis for a certain trait. Heritability is expressed in percentage, e.g. insulin-dependent diabetes mellitus has heritability of 70% and asthma – 60%, indicating a strong genetic predisposition (Book Rags Com 2006; Janson-Smith 2003). Scholars have been interested in twins since ancient times. So Hippocrates, the famous Greek physician living in the 5th c BCE, connected similar diseases in twins with material circumstances. The stoic philosopher Posidonius (1st c BCE) believed that similar diseases were caused by astrological circumstances. In the 4th c CE St Augustine of Hippo used the difference in fraternal twins Jacob and Esau in the Old Testament as an argument against the claims of astrologists that time of birth determined human personality and fate (Book Rags Com 2006). The modern history of twin studies began in the nineteenth century. In 1870s Darwin’s cousin Sir Francis Galton published several articles arguing that in determining the traits of twins heredity (nature) played a greater role that environment (nurture). Galton noted that twins provided a ‘naturally occurring experimental design’, a ‘living laboratory’ in which to study the effects of genes and environment. He pointed to the similarities in twins’ constitution and the tendency to develop similar diseases. Galton also suggested that identical twins might develop from a single egg and non-identical twins might develop from two separate eggs, which are fertilized and implanted simultaneously. This idea, published in Inquiries into Human Faculty and its Development (1883), was proved in the twentieth century. It was found out that that identical twins are monozygotic, while non-identical or fraternal twins are dizygotic. Galton had no necessary equipment to prove his guess (Book Rags Com 2006; Janson-Smith 2003). Since then, twin studies gained and lost its popularity among researcher at different times. Today the power of twin studies, providing a natural control for experiment, is widely recognized for the genetic and psychological research. New gene technologies provide an opportunity for genetic research of such diseases as cancer, arthritis, heart diseases and diabetes, to explore metabolic pathways, and discover new ways of treating diseases. Twin studies are carried out in the fields of embryology, biochemistry, immunology, genetic behaviorism, anthropology, sociology. However, twin studies have always been controversial in both ethical and scientific aspects. Galton’s tradition was extended by the American scientists at the University of Chicago. In 1937 Horatio Hackett Newman (b. 1875), Frank Nugent Freeman (b. 1880), and Karl John Holzinger (b. 1892) published their work Twins: A Study of Heredity and Environment, which became a landmark in the literature on nature and nurture. Later in 1940 Newman issued another book of his, Multiple Human Births: Twins, Triplets, Quadruplets, and Quintuplets, in which he speculated on the genetic and biological causes of miraculous birth and survival of Dionne quintuplets (b. 1934), who were in the centre of public interest at that time. On the bases of eugenics, twin studies acquired a more ominous character in Germany. So Johannes Lange (1891-1938) claimed that criminal propensities in one twin might increase the possibility of similar sociopathy in the other. British eugenicist John Burdon Sanderson Haldane (1892-1964) highly praised Lange’s book of 1929 Verbrechen als Schicksal: Studien an kriminellen Zwillingen (Crime as Fate: Studies of Criminal Twins), so that in 1930 it was published in England translated by Haldane's wife as Crime and Destiny. Due to the Nazi philosophy German twin studies of 1930s -40s were tightly associated with the questions of race. In 1935 Josef Mengele (1911-1979), a wealthy Bavarian and a member of the Sturmableitung (SA), received a PH.D. in anthropology at the University of Munich for his dissertation Race-Morphological Investigations of Sections of the Anterior Lower Jaw in Four Racial Groups. He continued his studies at the University of Frankfurt Institute for Hereditary Biology and Racial Hygiene and in 1937 he joined the Nazi party and Schutzstaffel (SS). In 1938 he got an M.D. for his second dissertation Genus Investigations on Cleft Lip, Jaw, and Palate. In May 1943 he was assigned to Auschwitz as camp physician, which gave him a chance to continue his studies, having an endless supply of subjects for his awful experiments. Vershuer, pinning great hopes on Mengele’s studies, provided him with anything he needed. Mengele became the camp’s major ‘selector’ deciding on lives and deaths of people. All twins were spared for Mengele’s study, marked by cruelty, arbitrariness and lack of scientific rigor. Mengele worked by the method of random trial and error, without any preliminary hypothesis. For instance, he tried to change brown eye color to blue, which resulted in infection, pain and blindness of his subjects. Not treating prisoners as human, Mengele kept his subjects naked to be able to observe and measure them easily. He would bleed, inject, dismember, transfuse or irradiate his twins, perform unconventional surgical procedures on them without anesthesia and expose them to diseases. Often he would kill one or both twins, dissecting their bodies and sending the results to Vershuer. More than 1,500 pairs of twins were involved into his experiments, only about 200 of those having survived. After the Second World War, Mengele escaped to South America. In 1959 he was named in the lists of “Nazi hunters”, and in 1964 his degrees were revoked. In 1985 one of the survival pairs of “Mengele Twins” Miriam and Eva Mozes (b.1935), established the international support group Children of Auschwitz Nazi Deadly Laboratory Experiments Survivors. Not all twin studies are so inhuman, useless and illogical. Yet, after the Second World War twin researchers had difficulties with getting approval for this kind of research. Only in 1951, Italian genetics Luigi Gedda published his Studio dei gimis (A Study of Twins), which became the first significant postwar book on twins and was partially translated in English. In the 1960s there was a splash of interest to twin studies, evoked by geneticists’ attempts to discover the causes of higher-order multiple births, which was the field of Newman’s interest. The experiments were revived in 1980s. Thomas Joseph Bouchard, Jr. (b.1937), professor of psychology at the University of Minnesota and director of the Minnesota Center for Twin and Adoption Research, is considered to be the leading scientific investigator of twins. From 1979 to 1999 his team conducted a broad registry project studying twins, the results being first published in 1990. They examined numerous pairs of male and female monozygotic and dizygotic twins, born in different periods of time, to check their hypotheses in the fields of psychology, medicine, development, sociology of emotion, etc (Book Rags Com 2006). For instance, their twin family studies concentrated on that how genes and environment interact forming character, values, strengths and vulnerabilities. Based on the facts that identical twins are genetic duplicates, fraternal twins share 50% of their genes and both types share common life experience, the scientists tried to determine how genes and environment influenced personality development, attitudes, talents and abilities, falling in love, divorces, vocational choices, aging, body characteristic and health, coping with stress, brain waves and other psychological responses. Many interesting facts have been discovered. They found out that similarities in twins’ personalities were caused by genes. Notwithstanding this fact, it turned out that many choices in our life are done almost randomly. So is our choice of mate, which is viewed as one of the most important we ever make. It proved to be not influenced by genes or upbringing, but resembles of a lottery. On the other hand, the studies have indicated that divorce rates depend on genetic characteristics. As growing up, MZ twins, becoming less similar in terms of physical traits like looks and weight, turned out to become more similar in terms of their abilities, vocabularies and arithmetic scores, which was not characteristic with fraternal twins. MZ twins also tend to have more similar ages at the time of death than DZ twins do. EEG study of brain waves showed that MZ twins usually generate the same amount of alpha waves and produce similar EEG spectra, which proves that EEG is determined mostly by genes. Genes also seem to influence the way our brain processes information (UMN Dept of Psychology Labs MTFS 2001). However, twin studies assumptions remain controversial, says James Jaccard, PhD, a psychologist studying statistical methods at the University at Albany of the State University of New York (In APA Online 2004). Random mating, equal environment, gene-environment interaction and active genetic mechanisms are the major limitations. Researchers work developing, improving and expanding twin study designs and statistical methods. Notwithstanding the fact that the assumptions question remains a stumbling block, most researchers agree that twin studies will continue to be an important tool in throwing light on human behavioral genetics, in future involving the combination of traditional twin studies and molecular genetics research (APA Online 2004). References: American Psychological Association Online. A second look at twin studies. Monitor on Psychology. Volume 35, No.4 April 2004. URL: www.apa.org/monitor/apr04/second.html - 18k (28.11.07.) Book Rags. Com. Twin Studies Summary. 2006. URL: http://www.bookrags.com/Twin_study (28.11.07.) Janson-Smith, Dierdre. Twin Studies. The Human Genome Site. March 19, 2003. URL: genome.wellcome.ac.uk/doc_WTD020902.html - 24k (28.11.07.) University of Minnesota Department of Psychology Laboratories. Minnesota Twin Family Study. 2001. URL: http://www.psych.umn.edu/psylabs/mtfs/special.htm (28.11.07.) Read More