What did the Minnesota study of Twins Reared Apart suggest about intelligence

In Dr. Andi Lassiter’s History and Systems of Psychology course, students complete a project on the local history of psychology. The goal of the assignment is to research some aspect of psychology in the upper Midwest, such as local asylums or people / events related to psychology. Students also need to creatively tell others about their findings, and can choose to write a blog post for this site as a way to communicate their findings. For more information on this assignment, just use the contact form on this website to get in touch and we can share more details.

By Joseph Miller

“The Jim Twins” – Ripley’s Believe It Or Not (2018)

The influence of genetics on the field of psychology has been a long and heated debate. As humans we often wonder what influences will affect our personality the most? Why am I the way I am? Why can’t I stop (insert detrimental undesired activity here)? The Minnesota Study of Twins Reared Apart sought to do just that. This study was a part of the larger program Minnesota Twin and Family Research, which started at the University of Minnesota and used twin pairings to investigate substance abuse and its relationship to genetics, finding that your genetics may play a bigger role than we think.

The Twin Study seeks to identify genetic and environmental influences on the development of psychological traits. Psychologist Thomas J. Bouchard led his team in a groundbreaking study that lasted 20 years (from 1979 – 1999) and studied 137 pairs of twins. This included 81 pairs of identical twins and 56 pairs of fraternal twins. This study emphasizes identical twins, as they share the same genes with each other, whereas fraternal twins will only share about half of these genes. It was important that the twins being surveyed in this study were separated early in life, ensuring environmental and genetic factors could be measured separately. The goal of this research was to determine the inheritability of traits such as academic ability, personality, relationships, and health (physical and mental). During the study pairs underwent approximately fifty hours of medical and psychological assessment, which used multiple tests designed to measure personality traits, occupational interests, and mental ability.

Perhaps the most fascinating finding of this study came in the discovery of the “Jim Twins”. Jim Lewis and Jim Springer were separated at birth, both were adopted by families living in Ohio that knew of the other twin brother’s existence, but did not where he ended up. The similarities coincidentally start with both sets parents naming their adopted boy “James”, and only gets wackier from there. Both boys preferred the nickname “Jim”, both had a childhood pet dog named “Toy”, and both enjoyed math and struggled with reading while in school. In adulthood both took jobs in security (Lewis as a security guard and Springer as a deputy sheriff). Don’t worry, their story continues to escalate into stranger territory. Both men were married and divorced, both first married a woman named Linda only to divorce her and remarry a woman named Betty. Both had a son they named James Alan (or spelled Allan in one case), and both men vacationed three blocks apart at the same Florida beach. The Jim’s suffered tension headaches and smoked Salem cigarettes. It seemed as if they had been living the same life without ever knowing each other. It wasn’t until they were 37 that the two brothers had even spoken to each other, when Jim Lewis asked and was given his brother’s information through a courthouse. Two years later the twins met in person. At this point their situation had caught plenty of attention, including that of Dr. Bouchard, who recruited them into the Minnesota Study of Twins Reared Apart. Predictably, he found the analyzation of their brave waves and personality tests to be “almost identical”.

The case of the “Jim Twins” is a sensational, some would say unbelievable story. Bouchard and his research team used their data, along with data from over one hundred pairs of twins, and concluded that genetics plays a key role in trait development. They also concluded that being “reared together” (a.k.a. being raised in the same household) had minimal effects on development. It was also found that identical twins will share a more similar body posture than fraternal twins. Research also found that genetics plays an influence in sexual orientation, religiousness, and reported well-being.

The conclusion that heredity is the main source of character traits is not without its critics. Arguably the most controversial conclusion drawn through the study is the researcher’s view on intelligence; “general intelligence or IQ is strongly affected by genetic factors”. From this notion stems the debated idea that IQ variation is roughly 70% affected by heredity, leaving only 30% to the environment. Critics have argued that this enables racism and other forms of oppression, such as economic inequality. These findings have been cited in support of genetic determinism, which similarly states that genetic roles are predominantly responsible differences in mental abilities and personal differences. The danger in this is the potential for us to defend the status quo in terms of forms of oppression, considering outcomes and inequalities as results of genetics and thus preventing the encouragement of effect change in these areas.

What do the findings of the Minnesota Study of Twins Reared Apart mean for those with genetic predispositions to low IQ, substance abuse, or born to parents with other struggles. What does it me for each of us?. Yes, the study does support the importance of genetics on our personal characteristics, but it does not guarantee our outcomes. This study can be helpful in identifying traits that we have generically inherited and be more aware of ourselves. Heredity has been found to play a large role in our development, but that does not discredit the effects that environment and decision making have in our daily lives or nurturing another human being. In the end it is best for us to recognize the role that our genes play, while also controlling what we can control, and blaming your parents for the rest.

References

Bouchard, T., Lykken, D., McGue, M., Segal, N., & Tellegen, A. (1990). Sources of human psychological differences: the Minnesota Study of Twins Reared Apart. Science, 250(4978), 223–228. https://doi.org/10.1126/science.2218526

Jay Joseph, P. D. (2018). Bad-Science Warning: The "Minnesota Study of Twins Reared Apart" (MISTRA). Mad In America. https://www.madinamerica.com/2018/11/bad-science-minnesota-study-twins-reared-apart/ .

Lewis, T. (2014). Twins Separated at Birth Reveal Staggering Influence of Genetics. LiveScience. https://www.livescience.com/47288-twin-study-importance-of-genetics.html .

Minnesota Center for Twin and Family Research. (n.d.). https://mctfr.psych.umn.edu/research/UM%20research.html .

Ripley's Believe It or Not!, Distasio, S., & Graziano, J. (2020). The Uncanny Case of the Jim Twins, Two Estranged Twins Who Led Identical Lives. Ripley's Believe It or Not! https://www.ripleys.com/weird-news/jim-twins/ .

What did the twins reared apart suggest about intelligence?

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