Two identical twin sisters, separated at the age of two, were brought up in entirely different nations and cultures, resulting in a notable difference in their IQ levels.
These sisters, who are now adults, were born in Seoul, South Korea, in 1974.
They lived together until their early childhood when a tragic incident occurred while their grandmother took them to a market.
One twin got separated from her family and became lost until strangers found her.
She was taken to a hospital located about 100 miles from her residence and later stayed with a foster mother.
Being only two at the time, the twin had no memory of the incident.
Eventually, she was placed in an adoption agency and adopted by a family in the United States.
Raised by her adoptive family in the US, she later provided a DNA sample to a South Korean program designed to reunite families.
Her DNA was entered into the system, and by October 2020, she discovered that she was not only a twin but also had a brother and another sister.
Upon this revelation, researchers from the US and South Korea conducted tests and interviews with the twins to evaluate their intelligence, personality traits, mental health, and medical histories.
The research concluded that the twins’ personalities were quite similar, aligning with previous studies showing moderate genetic influences on personality as adults.
Interestingly, the twin raised in Korea reported a harmonious family environment, in contrast to her sister in the US who faced familial conflict and the divorce of her adoptive parents.
“Notable is that both twins are distinctively high on Conscientiousness, indicating that both are purposeful, well-organized, dutiful, and achievement-striving,” the researchers noted in their publication in the journal Personality and Individual Differences.
While their similarities underscore the significance of genetics in shaping personality, the researchers were particularly surprised by the “substantial differences” in their IQ scores.
Previous research on identical twins suggested an average IQ difference of about seven points, yet this study revealed a 16-point lower IQ in the twin raised in the US.
“It is striking that the twins showed substantial differences in cognitive abilities that have been linked to strong genetic influence,” the researchers mentioned.
The time lapse between their separation and the testing makes it difficult to determine if their differing upbringings contributed to the IQ disparity, but the study did highlight that the US-raised twin had experienced three concussions, which could have affected her cognitive abilities.