Twins Reared Apart

An Analysis of the Minnesota Study of Twin Reared Apart
Abbie Barnes
The Minnesota Study of Twins Reared apart (MINSTRA) marked an important moment in in the field of developmental psychology. The academic environment surrounding the study was focused on the question of nature versus nurture. This question spurred interest in twins because of their unique nature of having the same or very similar genes. In February of 1979 “the Jim twins” were reunited. These identical twins were separated at birth but shared an alarming number of similarities such as same occupation and hobbies. This sparked public interest into this topic and was ultimately responsible for the start of the MISTRA (Segal, 2012, p. 13). This analysis will discuss
the processes and results of the study.
It will then discuss my own critique of the MISTRA including ideas on further research.
The MINSTRA: What was Done and How?
The MINSTRA was a thorough analysis of reared apart fraternal (DZA) and identical (MZA) twin pairs. Thomas J. Bouchard Jr, a psychologist with the University of Minnesota, started the MISTRA in March of 1979, and it lasted for twenty years (Segal, 2012, p. 3). Over the span of the 20-year study, thorough psychological and behavioral assessments of eighty-one MZA (monozygotic) and fifty-six DZA (dizygotic) reared apart twin pairs were conducted (Segal, 2012, p. 8). The goal of the study was to identify associations between differences in the twins’ life development and in the twins’ behavior (Segal, 2012, p. 3). If the MZA twin were more similar than DZA twins in certain behaviors, this was evidence of the influence
of genes (Okami, 2014, p. 120). The procedures of the study included approximately 50 hours of medical and psychological testing per set of twins (Bouchard, 1990, 223). The MISTRA study was an uniquely thorough assessment of each participant. More than one test instrument was used in each major category of psychological assessment to make sure that appropriate coverage of all psychological aspects. The twins were given a questionnaire including four personality trait records, and three occupational assessments of specific aspect of the twins’ developmental environment (Bouchard, 1990, 223). Different examiners administered an IQ test, life history questionnaire, psychiatric questionnaire, as well as complete sexual history. A mental ability battery was given in a group setting. The twins were separated for all aspects of the test, and were under the supervision of a staff member. (Bouchard, 1990,pm 223-228).
The Results
The study worked to prove the hypothesis that genetic differences affect psychological differences indirectly, by affecting the environment in which the child develops (Bouchard, 1990, 223).
Findings for the study were unexpected in the degree to which personalities between the MZA (reared apart) twins and MZ twins reared together were similar. The study largely found that there was little affect of being reared apart for the personality characteristics of the twins. Overall, Bouchard 's study had three main conclusions. The first was that general intelligence is strongly affected by genes; he concluded this by calculating that the IQs of the MZA twins correlated at .70 meaning that 70% of the IQ could be attributed to genes (Bouchard, 1990, p. 227). The second conclusion was that outside influences such as parents and society do not greatly confine personality differences. The third conclusion was that MZA twins are similar because their genes effect their developmental environments similarly (Bouchard, 1990,pm 227). These finding were impressive, but not immune to
criticism.
Critiquing the MISTRA
The MISTRA is well received by some academics, while others harshly criticize it (Segal, 2012, p.13). The study has a number of strength and weaknesses, as any academic work is prone to. One strength in this study it its ability to break the status quo on the prevailing psychological attitudes and beliefs at the time. At the time that the study was administered the prevailing academic view of psychology was the environmentalist one (Segal, 2012, p.4). The psychological environmentalist belief is that the environment, rather than ones genes, controls ones personality and behavior (Segal, 2012, p.11). This study makes and excellent argument against this belief. Another strength that this study has is the extent to which Bouchard assessed the twins’ personality and behaviors. The number of categories and extent of the questionnaires is thorough enough to not leave out many factors that contribute to ones personality. This study while ground breaking and extraordinarily thorough is not perfect.
The MISTRA includes a few weaknesses. Perhaps an inherent weakness in much twin research is the lack of a wide enough sample size to base scientific findings on. The MISTRA studies such a specific niche of twin, those reared apart. A large enough sample to more concretely identify results will never be found. Another critique of the MISTRA is that it was partially funded by the Pioneer Fund, an organization that has given grants to aid research on race differences in intelligence (Segal, 2012, p. 13). I am cautious as to the results of any research that receives funds from a institutions such as this. Overall it is important for academic studies to be critiqued to point out potential biases and sources of error in the research.
Beyond the MISTRA
Bouchard’s research is not the last word on studies concerning the influence of genes over that of the environment. There are other possible studies that I believe would provide incite into this topic. I think that subsequent research of this topic should investigate how adoptive children reared in similar environments compare to each other. These children should then be assessed on all of the personality and behavioral characteristics that Bouchard tested for. The results would give insight into the affect of rearing on non-related siblings. Though raised is nearly identical environments their behavioral and personality differences would point to their genetic differences.
If I were to do a similar study I would do a few things differently. I would investigate more variables than just psychological. I would also study their differences in income, health, education level, and marital status. These variables would give me a new perspective on their reactions to their differing environments. It would offer a look into the same question of genes VS. environment, but would give new variables with witch to compare.
Overall the MISTRA provided the academic community with groundbreaking research into the huge affect of genes on individual’s personality and behavior. It flew in the face of the prevailing environmentalist views of psychology. Though the study includes a number of criticisms, it also includes many strengths. The question of the influence of genes and the environment is a fascinating scientific subject that studies like this do an excellent job of answering.
Works Cited
Bouchard, T., Lykken, D., McGue, M., Segal, N., & Tellegen, A. (n.d.). Sources Of Human Psychological Differences: The Minnesota Study Of Twins Reared Apart. Science, 223-228.
Okami, P. (2014). Psychology: Contemporary perspectives. New York: Oxford University Press. Segal, N. L. (2012). Born together--reared apart the landmark Minnesota twin study. Cambridge, Mass.: Harvard University Press.