12 May 2022

A unique case

The level of intelligence depends more on upbringing than on genetics

Georgy Golovanov, Hi-tech+

A Korean woman raised in a foster family from the United States only found out that she had a twin sister when she became an adult. This melodramatic story gave scientists a unique opportunity to explore the degree of influence of culture on academic success and personality formation. The results were unexpected.

Science has long been arguing about what is more important in the formation of personality — heredity or upbringing, and what qualities of a child — or their absence — can serve as a fairly accurate sign of success in adulthood. Probably, it is impossible to express the contribution of both factors in quantity — people are very complex creatures, and it is unrealistic to conduct a strictly controlled randomized experiment of a lifetime. However, the Korean twins gave scientists a unique material for research, says ZME Science.

After one of the sisters shared her DNA in 2018 as part of a family reunification program, she learned about the coincidence of genetic material, and scientists from The University of California immediately began to conduct tests, assess living conditions, character traits, worldview and value system, medical history, as well as general intelligence and mental health.

One sister left in In Seoul, she was brought up in her own family, and the second one, which her grandmother accidentally lost in the market, was transferred to the guardianship authorities, and then got to her foster parents, who took her to States. There she was brought up in stricter conditions, and conflicts between her and foster parents arose more often.

The sisters' worldview turned out to be almost polar. The first demonstrated a collectivist model of behavior peculiar to Korea, putting the group above the individual, while the second, who grew up in the United States, shared individualistic values. But the difference in cognitive abilities was most striking. The sister who grew up in her own family received higher scores in the IQ test — the difference was 16 points.

Previous studies of identical twins who grew up together have shown completely different results. Scientists were shocked at how identical their brains looked in terms of structure and cognitive abilities. Then it was concluded that the level of intelligence is an innate thing.

"Unlike previous studies, the general intelligence of twins and the level of nonverbal thinking showed noticeable differences," says an article published in the journal Personality and Individual Differences (Nancy L.Segal & Yoon—MiHurb Personality traits, mental abilities and other individual differences: Monozygotic female twins raised apart in South Korea and the United States published in the journal Personality and Individual Differences – VM).

As for personal qualities, both sisters turned out to be extremely similar: their conscientiousness and neuroticism indicators were equally high, the level of job satisfaction coincided, although one worked as a cook and the other as a civil servant.

Perhaps sequencing the genome of these unique twins will give scientists new food for thought.

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