In 1976, a two-year-old girl was found alone in a market in Seoul, South Korea. She was taken to the hospital where she was diagnosed with measles and, as she could not be identified, the girl was placed in the adoption system.
She was later adopted and raised in the United States by an American couple, but decades later, as an adult, the woman would learn that she had an identical twin sister.
Interestingly, the two are surprisingly different in many ways, researchers have found in a new study appearing in the journal Personality and Individual Differences.
Culture Matters More Than Previously Thought
It would be difficult for anyone to deny that education plays a fundamental role in the formation of individuals, whose quality, or lack thereof, has been found to be elements of success in adulthood.
But genes, which can shape intelligence and athletic performance, or predispose people to disease, also play a role in our development. But how much?
Defining people’s capabilities is very complicated and answering these questions would require a strictly controlled randomized experiment, and as we all know, life doesn’t really work that way.
Nevertheless, South Korean twins provide a unique opportunity. After her sister in the United States submitted her DNA in 2018 as part of South Korea’s program to reunite family members, there was a match, and scientists immediately jumped on board to run some tests on the twins.
Nancy L. Segal, professor and director of the Center for Twin Studies at California State University, Fullerton, evaluated the family background, personality traits, worldview, and value system of each twinin addition to medical history and aspects such as general intelligence and mental health.
In the course of their investigation, Segal and his colleagues learned that the twin from South Korea grew up in a supportive and cohesive family. His adoptive sister was not abandoned; her disappearance was an accident due to the negligence of her grandmother, who basically lost her in the market. In the meantime, the twin who grew up in the United States was raised by a family in a stricter and more religious home where there was more conflict.
Perhaps not so surprisingly, the sisters’ nearly opposite family backgrounds shaped radically different models of how they see the world:
· The sister raised in South Korea had more collectivist values (morals and social behaviors that favor the group over the interests of its individual members).
· The twin who grew up in the United States had individualistic values.
But what stood out was the huge difference in cognitive abilities between the two sisters. The woman raised in South Korea scored considerably higher on intelligence tests than her sister from the United Stateswith an overall IQ difference of 16 points.
Other studies of identical twins
Previously, a 2001 study from the University of California, Los Angeles put 10 pairs of identical twins and 10 pairs of fraternal twins through a series of tests that examined 17 separate abilities, including verbal and spatial working memory, attention tasks , verbal knowledge, motor speed and visuospatial ability.
The researchers also performed MRIs to scan each volunteer’s brain. When they compared each pair of twins, the researchers were surprised at how similar their brains were to each other, both in terms of structure and cognitive abilities, leading them to conclude that IQ is inherited.
Identical twins often seem to have similar life paths. Scott and Mark Kelly are identical twins, and they both made it amazingly successful to become NASA astronauts, traveling to the International Space Station. Nevertheless, new study suggests one’s family background can drastically alter a person’s life, even between twins.
Of note is the fact that the two reunited South Korean sisters had very similar personalities, with both scoring high on measures of conscientiousness and low on measures of neuroticism.
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