Case Study: Identical Twins Reared in Different Cultures

Twins raised apart are highly valued in psychological research. Studies have shown that genetic factors underlie a wide range of behaviors, including, intelligence, personality and interests. Twins raised apart in different countries are a unique subset of twins reared apart. They are also very informative for revealing the extent to which cultural factors may affect the similarity of identical twins-- therefore, it is very important to include such cases in the general and professional literature.

I have written about a number of such cases and was fortunate to discover several new cases quite recently. My latest report concerns identical South Korean female twins, one raised in South Korea (K) by her birth parents and the other raised in the United States (U) by her adoptive parents. The circumstances of their separation are extraordinary.

When and How Were The Twins Separated?

The twins were born in 1974. When they were two years old their grandmother took them to a market. Somehow, U got away, was picked up and brought to a hospital. She then entered a foster home before being transferred to a baby care facility. Her case was eventually managed by the Holt International Adoption Agency whose staff arranged for her to be adopted by a couple from the United States.

U’s biological mother and father were desperate to find her. They distributed printed information asking for help, and they also went on a television program for missing persons.

Discovery of Separation and Twinship

As part of South Korea’s program for reuniting adopted-apart family members, U sent a DNA sample to the data bank. In March of 2020, she received a telephone call that was life-changing---her biological mother had been identified in South Korea. During an online meeting several months later, U learned that she had a twin sister, as well as a biological brother four years older and a biological sister two years older.

Case Study

I learned about U and S when I did an interview and discussion for a group called Boston Korean Adoptees (BAK), Inc. That session took place in October 2020.

I contacted my South Korean colleague, Dr. Yoon-Mi Hur, a faculty member at Kookmin University and Director of the Kookmin Twin Research Institute, in Seoul. She and I have collaborated in the past on similar case studies. We agreed that Dr. Hur would study S, I would study U, and then we would combine our results. Each twin completed a general ability (Wechsler IQ) test, administered by a trained assistant in their respective countries. The twins also completed an array of other protocols, such as a life history interview, self-esteem survey, family environment form, personality questionnaire, job satisfaction survey, individualism-collectivism assessment, and twin relationship questionnaire. I will focus on selected aspects of this case study. At the end of this essay I will provide a source for finding additional information.

Findings

The twins’ parents and families were very different as indicated by the family environment form. For one thing, S grew up in a more nurturing and supportive environment than U. Nevertheless, the twins showed favorable and similar levels of self-esteem, suggesting genetic effects. They also showed similar performance in personality, e.g., in the trait of conscientiousness. However. their general ability scores were quite different—U scored 84, while S scored 100. Their difference of sixteen points exceeds the mean difference of 6 points reported for identical twins reared together. This could be partly due to U’s history of concussions, which also may have affected her performance on a test of non-verbal reasoning. U also described herself as having a history of being a poor test-taker. However, the twins did show similarities in selected subtests that comprise the Wechsler test. Perhaps the most interesting outcome for me and for my collaborator concerned the twins’ score in individualism-collectivism.

Here, U’s scores show that she perceives the self as autonomous and believes that members of a collective are equal in status. This suggests that U has adapted well to American culture. S’s scores suggest that she perceives the self as a part of a collective and is willing to accept hierarchy and inequality within that collective. This is consistent with the South Korean culture of her age. In sum, the United States is largely an individualistic culture, while South Korea is mainly a collectivist culture. The twins’ scores reflect the importance of culture on their respective value systems.

Summary

The twins described here offer a look into how rearing in different environments and cultures can affect people with identical genetic endowments. Cultural climates can modify values, as shown by the individualism-collectivism assessment. It is likely that other transnational reared-apart identical twin pairs will be identified; in fact, I am working with some pairs because it is important to include them in future studies.