Comparing the traits of identical siblings sheds new light on the centuries-old debate as to whether innate genetic traits, or upbringing, environmental influences are more dominant.
One of the twins was lost in the market
An identical pair of twins was born in 1974 in Seoul, South Korea. The girls were separated at the age of two when one of the twins was lost in a market.
Despite her parents appearing on a television show about missing persons, the little girl could not be reunited with her family and
it was eventually adopted by an American couple.
Growing up in the states, the adopted twins didn’t even know they had any siblings at all until they submitted their DNA to the South Korean reunification program in 2018. Two years later, he received the news that he had not only an identical twin brother, but also an older brother.
After reuniting them, the twins completed a series of tests designed to assess intelligence, personality profile, mental health, and health history. The results showed that the IQ of the twin brother, who grew up in the United States, was 16 points lower than that of his South Korean-educated brother.
The result contradicts all studies to date
The finding contradicts previous studies with identical twins, which found an average IQ difference of seven points. Commenting on the unexpectedly large gap between the two brothers, the authors of the study wrote:
it is striking that the twins showed significant differences in cognitive abilities associated with a strong genetic effect.
Genetics or upbringing?
Whether this discrepancy was caused by the different upbringing of the twins is difficult to say, although researchers note that the nurse, who grew up in the United States, suffered from three previous concussions that may have affected her cognitive abilities.
The role of genetics
Continuing the pair’s evaluation, the researchers further revealed that the general personality traits of the twins were similar, consistent with the literature on moderate genetic effects on adult personality.
It is noteworthy that both twins have a distinctly high level of conscientiousness, indicating that they are both purposeful, well-organized, dutiful, and performance-minded.
The fact that these similarities persisted despite the brothers ’conflicting life experiences and home environment is interesting and highlights the role that genetics plays in determining an individual’s temperament.
The effect of different upbringing
While the twin brother, who grew up in South Korea, reported growing up in a loving and harmonious family home, the adopted nurse reported a tougher upbringing colored by regular conflicts and divorce from adopted parents. Nevertheless, the sibling’s self-esteem scored the same and showed a very similar mental health profile.
The couple also had a common medical history: they both underwent a surgery to remove a tumor from their ovaries.
However, the twins differed in terms of culturally ingrained ideologies. The brother, who grew up in the United States, had a more individualistic attitude, while the girl, who grew up in South Korea, had more collectivist values.
Understandably, there are rare cases where twins are reared separately, and several such cases need to be studied before definite conclusions can be drawn. Nevertheless, this study provides an impressive new insight into the genetic, cultural and environmental factors that affect human development, writes IFLScience.