Scientists used a rare opportunity to study identical twins. They were separated early in life. They grew up in different families and different countries. The researchers received surprising results.
- Twins usually achieve comparable results on intelligence tests
- The siblings, separated for 26 years, despite the fact that they grew up in different homes, with different cultures and values, had similar personalities, self-esteem and medical history, although their level of intelligence differed
- For scientists, this is just the beginning
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The level of the intelligence quotient of twins
IQ intelligence quotient – as shown – in 80 percent. is inherited. Twins most often have similar results in intelligence tests. In this case, however, there was a significant, as much as 16-point difference between the siblings.
This called into question the idea that intelligence may not depend so much on genes as on the environment in which we grow up.
“The similarities were evident in personality, self-esteem, mental health, job satisfaction and medical history,” the researchers wrote in their article.
At the same time, they emphasized that, unlike previous studies, the twins’ general intelligence and reasoning showed some marked differences.
The story of the twins
A pair of twins was born in South Korea in 1974 and separated at the age of two after one sibling got lost at a market. After being transported to the hospital, which was about 160 km from the family home, despite the efforts of the biological family to find the lost child, the child was eventually adopted by a couple from the United States.
The twins met again in 2020, when the U.S. one provided a DNA sample as part of a South Korean family search for children lost by families. Researchers then contacted the couple and conducted a series of tests and interviews.
Despite many similarities – including in terms of mental health and job satisfaction – the home-raised twin in South Korea scored higher in terms of perceptual reasoning and processing speed.
While the results are clear, the cause is not. The researchers note that the child raised in the USA suffered three concussions as an adult, which made her feel like a “different person”. However, it cannot be said with certainty whether this affected the results obtained in the cognitive tests.
It is also worth considering that the family homes in which the twins grew up were not at all similar to each other. Moreover, they were located in completely different parts of the world. Scientists say there was more conflict and less freedom in the American home than in South Korea.
“Twins grew up in very different environments, apart from different countries and cultures” – noted the researchers.
What the study also supports in terms of nature versus parenting is that certain behavioral traits can remain the same even when children are raised in different environments. The twins scored high in terms of levels of conscientiousness and self-esteem, for example.
Overall, the United States is more individualistic and less collectivist in terms of national culture than South Korea. Scientists believe that these cultural differences likely had an impact on some personality outcomes.
The findings make fascinating reading, although you shouldn’t draw too many unequivocal conclusions from one single example of twins. On the other hand, it seems that the proliferation of readily available DNA tests in the coming years is likely to result in more discoveries of twin pairs that were separated in childhood. This will help scientists further investigate the issue.
“We need to identify more of these, if there are any,” evolutionary psychologist Nancy Segal of California State University, the study’s first author, told PsyPost. She also noted that we still do not understand all the mechanisms that are involved here, from genes at the molecular level to the behaviors we observe on a daily basis.
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