Psychologists found a “striking” difference in intelligence after examining twins

A new study of monozygotic twins raised apart in South Korea and the United States provides unique insight into how genetic, cultural, and environmental factors influence human development. 

The new research has been published in the scientific journal Personality and Individual Differences.

“I have studied identical twins reared apart for many years. 

They pose a simple, yet elegant experiment for disentangling genetic and environmental influences on human traits. \ 

This case was unique in that the twins were raised in different countries,” said researcher Nancy L. 

Segal, a professor and director of the Twin Studies Center at California State University in Fullerton.

The twins were born in 1974 in Seoul, South Korea. 

One of the twins became lost at age two after visiting a market with her grandmother. She was later taken to a hospital that was approximately 100 miles away from her family’s residence and diagnosed with the measles. 

Despite her family’s attempt to find her, she was placed into the foster system and ended up being adopted by a couple residing in the United States. 

In the new study, the twins completed assessments of family environment, general intelligence, nonverbal reasoning ability, personality traits, individualism-collectivism, self-esteem, mental health, job satisfaction, and medical life history. 

In the new study, the twins completed assessments of family environment, general intelligence, nonverbal reasoning ability, personality traits, individualism-collectivism, self-esteem, mental health, job satisfaction, and medical life history. 

They also completed structured interviews about their general life history.

Not only did the twins experience different cultures growing up, they also were raised in very different family environments. 

The twin who remained in South Korea was raised in a more supportive and cohesive family atmosphere. 

The twin who was adopted by the U.S. couple, in contrast, reported a stricter, more religiously-oriented environment that had higher levels of family conflict.