From: mars1933@hotmail.com   
      
      The Minnesota Study of Twins Reared Apart (MISTRA) is one of   
   the most important psychological studies of the last 50 years. It   
   began in 1979, at a time when it was widely believed that intelligence   
   and personality were almost infinitely malleable by the environment.   
   By the time the study ended 20 years later, it had played a key role   
   in overthrowing this dogma. It established beyond any doubt that genes   
   are crucial to who we are.   
      
       Long before MISTRA, it was well known that MZ twins acted very   
   similarly, but environmental theory held that this was because they   
   had grown up in the same environment and had been treated   
   similarly. Sometimes, however, twins have been separated at birth and   
   reared in different households. If separated MZ twins have similar   
   abilities and personalities, this cannot be because they had the same   
   family environment; it must be because of their genes.   
      
      Almost invariably, the reunion of identical twins was a joyful   
   event. Some spoke of the "ecstatic shock" of discovering someone so   
   similar. After just a short time together, most MZAs felt closer to   
   their twin than to adoptive siblings they had known all their lives.   
      
      During the evaluation week, twins completed about 15,000 paper-   
   and-pencil test items, and were examined for everything from gum   
   disease and tooth formation to heart function and blood composition.   
   There have been other studies of twins reared apart, but none that   
   gathered so much information. MISTRA data are still being analyzed   
   for research papers.   
      
       MISTRA yielded what amount to two different kinds of findings:   
   quantitative and impressionistic. The former come from personality,   
   intelligence, medical, and other testing, whereas the latter include   
   the almost eerie, unmeasurable ways in which MZA twins are alike.   
      
      The first twin pair MISTRA evaluated was particularly striking.   
   The two men met when they were 39, and found that both had been in   
   law enforcement but were now working as firemen. Both had loved   
   math in school and hated spelling. Both did woodworking as a hobby,   
   and their favorite vacation spot was Pas Grille Beach in Florida. One   
   had named his son James Alan and the other had named his James Al-   
   lan. They looked very much alike, had the same smoking habits, and   
   always held a beer can with a pinky under the can. Both had put on 10   
   pounds at the same age for no apparent reason.   
      
      Not all twins were so alike, but this book is full of astonishing   
   similarities. In one MZA pair, one twin was reared in Germany and the   
   other in Trinidad, and they had never met before they came to Minne-   
   sota for testing. When they arrived at the airport each was wearing a   
   light blue shirt with epaulettes, and wire-rimmed glasses. They both   
   collected rubber bands, which they wore around their wrists, and   
   washed their hands both before and after using the bathroom. Both   
   liked to startle people by sneezing loudly in elevators.   
      
      One pair of MZA women both wet the bed until age 12 or 13. When   
   they were teenagers they started having nightmares about the same   
   things: fishhooks and doorknobs. Both had problems with nightmares   
   for more than ten years.   
      
      A pair of female MZA twins from Australia found each other because   
   of a case of mistaken identity. They both worked as fashion buyers for   
   competing department stores, and a customer accused one of   
   moonlighting for the competition. They were both very elegant,   
   dressed with the same style and the same kind of jewelry, smoked the   
   same cigarettes, and had the same hairstyle, posture, tastes, and   
   speaking voice.   
      
      One MZA pair of male twins were both fitness fanatics who ran their   
   own bodybuilding gyms. MZA twins generally have the same posture and   
   arrange their hands and legs in the same way while dizygotic twins do   
   not.   
      
      Prof. Bouchard, who ran MISTRA, once had occasion to meet a man   
   who had run a smaller-scale MZA study in Denmark in the 1960s, and   
   asked him if he had found such astonishing similarities. The man   
   replied that he had, but he did not report them because was no way to   
   measure such similarities-and he was afraid no one would believe   
   him.   
      
      Prof. Segal writes that it was "thrilling" to get to know MZAs and   
   discover how similar they were, but she, too, was frustrated because   
   it was not possible to measure or assess similarities in complex   
   behavior. She notes that when she interviewed MISTRA people to write   
   this book, many looked back with nostalgia on the excitement of their   
   discoveries. One researcher who administered intelligence tests to the   
   twins wished that he had filmed them taking the tests. As he wrote:   
   I sat quietly behind them. The strategies [for answering test   
   questions] were so different between pairs but within the MZA   
   pairs they were so similar. Both twins vocalized or turned   
   around or stared at the screen or solved the problems quickly. It   
   was amazing. I smiled to myself when I saw these things, think-   
   ing no one would believe me.   
      
      Of course, there were many findings that could be quantified, the   
   most obvious being intelligence. There is no better way to measure the   
   heritability of intelligence than to study MZA twins.1 Because their   
   environments are completely different-though not so different as to   
   include malnourishment or physical abuse-similarities in IQ can   
   have only genetic causes. Test results of such twins are often so   
   similar that it is like testing the same person twice.   
      
      The test results that certainly caused the most surprise were   
   measures of personality. At the time, it was common to assume that   
   personality was formed almost exclusively by family influence. It is   
   not; it is formed in about equal parts by genes and by what is called   
   "non-shared environment," or the micro-environment each person   
   makes for himself. Parents think they have a lot of influence over how   
   their children turn out, but they flatter themselves.   
      
      MZT twins (identical twins reared together) have very similar-but   
   not identical-personalities. People always assumed the similarities   
   came from growing up in the same environment. But MZA twins also   
   have very similar-but not identical-personalities, and there is no   
   detectable difference in the degree of similarity between twins who   
   grew up together and twins who grew up in different families sometimes   
   in different countries. The household, or the "shared environment,"   
   has very little effect on personality, at least by the time people are   
   adults.   
      
      Likewise, when biologically unrelated children are adopted and   
   reared in the same home, they may resemble each other slightly when   
   they are small, but as they grow up they become as different as com-   
   plete strangers. It is well known that shared environment can have an   
   early effect on IQ as well. "Virtual twins," or unrelated children of   
   the same age who grow up together, have a correlation of 0.3 for IQ at   
      
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