“Personality Traits, Mental Abilities and Other Individual Differences: Monozygotic Female Twins Raised Apart in South Korea and the United States”, 2022-08-01 (; backlinks):
[n = 1, MZA] Twins reared apart are rare, especially twins raised in different countries and cultures.
This report documents the behavioral, physical, and medical similarities and differences of monozygotic female co-twins, raised separately by an adoptive family in the United States and the biological family in South Korea.
Similarities were evident in personality, self-esteem, mental health, job satisfaction and medical life history, consistent with genetic influence found by the Minnesota Study of Twins Reared Apart and related studies. An overall twin correlation across 38 measures was r = 0.95, p < 0.001. In contrast with previous research, the twins’ general intelligence and non-verbal reasoning scores showed some marked differences.
Adding these cases to the psychological literature enhances understanding of genetic, cultural, and environmental influences on human development.
[Keywords: twins, adoption, personality, culture, intelligence, values]
…1.2. Twins’ separation and discovery: SK and US were separated due to unusual circumstances. They were born in 1974 in Seoul, South Korea. At age 2, their maternal grandmother took them to a market where US was lost. US was later seen wandering alone before being taken to a hospital where she was diagnosed with the measles; the hospital was ~100 miles from her family’s residence. US then entered a home of a loving foster mother, then transferred to the then Kyong Dong Baby Home in Suwon City. Her case was eventually managed by South Korea’s Holt International Adoption Agency whose staff arranged for her adoption by a United States couple. She has no recollection of having been lost. The twins’ biological parents circulated flyers in the hope of finding her and appeared on a television program for missing persons.
US submitted a DNA sample in 2018 as part of South Korea’s program for reuniting family members. In March 2020, she received a telephone call informing her of a genetic match—her biological mother had been identified in South Korea. During an online meeting in October 2020, US learned that she had not been born on April 25, but on October 8. She also learned that she has a twin, a biological brother 4 years older and a biological sister 2 years older.
…US had 3 concussions as an adult, caused by car accidents and from falling on ice. The most recent and severe incident occurred in January 2018, resulting in classic symptoms of light sensitivity and concentration difficulty. US feels she is a “different person”, with increased anger and anxiety. She requires additional time to process information in some problem-solving situations, although she has always seen herself as a poor test taker.
…US obtained a score of 31 on the SPM. US’s testing time was 105 min, but she stopped at D7 (42 items) from frustration with difficult items. SK completed all 60 items in 54 min with a score of 43.
…[contrast 2014] It is striking that the twins showed substantial differences in cognitive abilities (WAIS IV and SPM) that have been linked to strong genetic influence. In composite scores of the WAIS-IV, they were nearly identical in WM and VC, but US was considerably lower than SK in PR and PS, with an overall IQ difference of 16 points. The mean IQ difference for MZA twins in the MISTRA was 7.07 (SD = 5.83), with a range of 0–29 points. Larger IQ differences in some MZA pairs were variously associated with brain damage resulting from accidents (Born together—reared apart: The landmark Minnesota twin study, 2012). US’s SPM score was also considerably lower than SK’s score. Given that the SPM measures reasoning abilities to form perceptual relations and identify perceptual distractors, independent of language (Van der 2000), and that US worked much longer than SK, it can be concluded that US is lower than SK in perceptual reasoning and processing speed. US’s lower scores in these cognitive domains may reflect her history of concussions.
2012, pg206:
An interesting and novel feature of David DiLalla’s work was the multivariate profile analysis, looking at the score elevation and tracing the peaks and valleys of the twins’ MMPI scores. The average score elevation looks at each twin’s average scale score, while the profile shape looks at the difference of each twin’s MMPI scale from the average…In one case, the twins became discordant for major affective disorder with psychosis, and in the other case a head injury 5 years before assessment had probably caused neurological damage in one twin. These last 2 cases showed that MZA twins raised in the same culture could differ in personality and psychopathology for a variety of reasons.
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