Massive IQ Difference Between Identical Twins Raised Separately in the US and Korea

Photo by Tim Bish on Unsplash




The cognitive capacities of a pair of identical twins who were raised in different nations showed unexpectedly huge differences while displaying remarkably similar personality qualities. A comparison of the traits of the monozygotic siblings provides fresh insight into the age-old nature vs. nurture argument.

The sisters, who were split up at the age of two when one twin got lost in a market, were born in Seoul, South Korea, in 1974. The young girl was unable to be reunited with her family despite the fact that her parents had been on a television program about missing people, and she ultimately ended up being adopted by a couple in the US.

The adoptive twin didn’t discover she had any siblings while growing up in the United States until she provided her DNA to South Korea’s family reunion program in 2018. She learned two years later that she had an older brother and sister in addition to an identical twin.

The twins took a number of tests once they were reunited in order to evaluate their intelligence, personality traits, mental health, and medical background. Surprisingly, the twin who was raised in the US had an IQ that was 16 points lower than the twin who was nurtured in Korea.

The discovery, which was made and reported in the journal Personality and Individual Differences, deviates from earlier research on monozygotic twins, which suggested an average IQ difference of no more than seven points. The study’s authors note that “it is notable that the twins revealed major disparities in cognitive abilities that have been related to strong hereditary influence” in their analysis of the sisters’ unexpectedly wide gap.

It is difficult to determine whether this discrepancy was brought on by the twins’ distinct upbringings, although the researchers do point out that the sister who was raised in the US had previously experienced three concussions, which may have affected her cognitive abilities.

The twins’ general personality configuration was comparable, in line with evidence on mild hereditary influences on personality in adulthood, the researchers continue in their analysis of the pair.

It is noteworthy that both twins score highly on conscientiousness, indicating that they are both goal-oriented, well-organized, devout, and achievement-driven. It’s intriguing that despite the sisters’ divergent life experiences and upbringings, these similarities persisted, highlighting the important role that genetics play in defining a person’s temperament.

For instance, the adopted sister recalled a tougher upbringing, marked by ongoing conflict and her adoptive parents’ divorce, in contrast to the twin raised in Korea who spoke of growing up in a loving and peaceful family environment. Despite this, the two had very similar mental health profiles and identical self-esteem scores.

They both had surgery to remove malignancies from their ovaries, and they discussed certain parts of their medical backgrounds. The twins did, however, have different culturally imprinted ideas; the twin raised in the US displayed a more individualist outlook, whilst the twin raised in Korea displayed more collectivist views.

Due to the rarity of twins being raised independently, additional examples need to be investigated before any definitive conclusions can be made. However, this research offers some intriguing new perspectives on the genetic, cultural, and environmental elements that affect human development.


Discussion Questions

  1. How do monozygotic twins develop differently when they are raised in different environments?
  2. How do their differences in upbringing affect their personality and behavior?
  3. Can genetics alone explain the similarities and differences between monozygotic twins raised in different environments?
  4. How do environmental influences such as parenting styles and culture shape the development of monozygotic twins?
  5. What are some examples of monozygotic twins who have grown up to have very different lifestyles and careers?
  6. How do monozygotic twins who were raised in different environments react to meeting each other for the first time as adults?
  7. What are the benefits and challenges of being a monozygotic twin raised in different environments?
  8. Can monozygotic twins who were raised in different environments form a close bond as adults?
  9. How do monozygotic twins who were raised in different environments compare to dizygotic twins in terms of similarities and differences?
  10. How does the study of monozygotic twins raised in different environments contribute to our understanding of nature versus nurture?










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