A study of a pair of twins who were raised separately across the world from each other has revealed location can have a significant impact on intelligence.
The twin girls, born in Seoul, South Korea, in 1974, became separated at the age of two when one of them got lost at a market.
Despite her parents' appeal to find their missing daughter, she was not reunited with her family and was eventually adopted by a couple from the US.
Growing up on American soil, the twin was completely unaware she had any siblings at all until 2018, when she submitted her DNA to a South Korean program that aimed to reunite lost family members.
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In 2020, she discovered she not only had a twin but also an older brother and sister.
When the twins were finally reunited, they completed a series of tests designed to assess their intelligence, mental health, and medical history; resulting in a groundbreaking study of seperate identical twins.
Incredibly, the Korean-raised twin had a significantly higher IQ, coming in at a whopping 16 points over her sister.
The findings of the study, published in the journal Personality and Individual Differences, have contradicted previous research on identical twins, which indicated a difference of no greater than seven IQ points between twins.
While researchers were not able to conclude that the IQ difference was directly related to their difference in geographical location, the twins did have very different upbringings that could have contributed.
The sister who grew up in the United States suffered three concussions throughout her life, which can significantly impact cognitive capacity.
The twin raised in Korea grew up in a happy, harmonious home, whereas the US-based twin had a more turbulent childhood. She lost her family, found a new one, and conflict in her new home resulted in the eventual divorce of her adoptive parents.
Despite these differences, the pair had identical scores for self-esteem and mental health profiles.
Researchers found that 'the overall configuration of the twins' personality was similar, consistent with literature on moderate genetic influences on personality in adulthood',
"Notable is that both twins are distinctively high on conscientiousness, indicating that both are purposeful, well-organised, dutiful, and achievement-striving," the research paper said.
This shows that despite the difference in their upbringings, the two sisters had similar personalities, values, and approaches to life, highlighting that genetics could have a significant impact on personality.
So, to the eternal question: is it nature versus nurture? The jury is still out. It's too hard to tell.
Rachel Lang