Twins separated for 44 years, one in Korea, one in America, how did they grow up differently?

Is our intelligence determined by our genes or our upbringing? That is a question that scientists often ask. In several studies, scientists tested the IQs of identical twins (also known as monozygotic twins).

They confirmed that IQ is determined by up to 80% by genetics and that twins often have IQ differences of no more than 7 points.

Twins usually have IQ differences of no more than 7 points.

But there is a problem, the studies mentioned above were based on twins who were raised in similar educational and cultural environments. It was not until recently that a study published in the journal Personality and Individual Differences found a unique set of twins in the world to compare.

These two children grew up in two very different cultures. They were originally Korean twin sisters, but lost each other in 1976. At that time, both were just 3 years old.

A unique research opportunity

It all started one morning in 1976, when one of the two Korean sisters got lost while shopping with her grandmother. Someone found the helpless child that was not received and brought it home. The child then developed a fever from measles and was admitted to a hospital 100km away from the family's former residence.

Despite search efforts, the child's family was unable to locate their child. The mother then opened a shop in the market her child went missing, to watch each child go through there every day.

She didn't know her child had been placed in an orphanage and ended up being adopted by a foreign couple. They brought this child to the US, while the twin sister remained in the Korean family.

Yoon Sang-hee and Yoon Sang-ae in childhood.

It was not until 2020, in a program to search for missing relatives, that the lost twins found each other again. Scientists accidentally saw the show, too, and they immediately jumped at the opportunity to do a study.

Professor Nancy L. Segal, director of the Center for Twin Studies at California State University at Fullerton, said:

"I've been studying identical twins raised apart for many years. They set up a simple yet powerful experiment to sort out the effects of genetics and environment on the offspring's traits. People".

"This case is unique in that the twins were brought up in two very different cultural backgrounds."

How did the two children grow up differently?

In the new study, Korean twins completed interviews about their family environment, medical history, an IQ test, and a test of nonverbal reasoning.

Through these surveys, scientists can further assess their personality traits, individualism-collectivism, self-esteem, mental health as well as their job and life satisfaction. .

The results showed that during their 46-year separation, the twins experienced quite contrasting cultures and family environments.

Yoon Sang-hee and Yoon Sang-ae, one became a government employee while the other was a chef.

The child who remains in Korea is brought up in a warmer and more cohesive family atmosphere. In contrast, the twin adopted by an American couple lived in a strict, religious environment and experienced higher levels of family conflict.

Her adoptive parents eventually divorced and she says she suffered 3 major traumatic events in her life. It was the events that made her a different person, she said.

However, no matter what happens, it is a fact that the twins' DNA is identical. Surveys also show that despite their different living environments, they have pretty clear similarities in personality, self-esteem and mental health.

Both the medical histories of these twins are quite similar. They also reported similar levels of job and life satisfaction - although their jobs were quite different, one was a chef, the other was a government employee.

"These findings suggest that despite cultural differences, identical twins share some characteristics that remain remarkably similar, suggesting that they are the result of genetic influence," the professor said. Monk Segal said.

In addition to a twin sister, Denise McCarty (Yoon Sang-ae) has an older brother and a mother.

"However, in contrast to previous studies, there was a marked difference in IQ and nonverbal reasoning ability of these twins," added Professor Segal.

Accordingly, the child raised at home in Korea scored higher in reasoning ability and processing speed. The difference in IQ scores of these twins is also up to 16 points, a very high level compared to the figure of about 7 points in common twins.

In keeping with the cultural environment, a child raised in the US also has more personal values, while a child raised in Korea has more collective values. The researchers think that these cultural differences may have an impact on some of the reported personality scores.

"For these twins, we found that the influence of genes on their development was stronger. However, environmental influences were also important. The sisters showed differences. culturally distinct in some respects," said Professor Segal.

To better understand the influence of genes and environment on human development, scientists will need to look for more cases like these Korean twins to compare.

"We need to identify more such cases if there are any," Prof Segal said. Future similar studies will eventually tell us: will genes or upbringing determine more about each aspect of human growth?