Identical twins raised in Korea and the US show surprising differences in IQ, new study reveals

Twins are known for their similarities and close bond. However, one of the most unique and remarkable aspects of twins is their differences. A study published in Science Direct revealed that despite the many similarities identical twins share, there are impressive differences as well. A pair of identical female twins were raised separately in Korea and the US. Upon further analysis, they showed several differences in their IQ and development. The study aimed to understand the ongoing “nature vs nurture debate,” per IFL Science.

The twins were born in South Korea in 1974 and were together up to the age of 2. Unfortunately, the duo was separated after getting lost at a market. One of the twins couldn't be located despite their parents’ efforts. While one of the sisters was raised in Korea, the other was adopted by a couple in the US and has been separate ever since. It was only in 2018 that the sister in the US realized that she had an identical twin and a brother and sister too. The woman had handed over her DNA to South Korea’s program for reuniting family members where she discovered she was a twin.

Despite being identical, the twins exhibited differences due to their different upbringings and environments. They completed a series of tests assessing their personalities, mental development, and other factors, revealing distinct results. The sister raised in the US had an IQ 16 points lower than her sibling in Korea. Previous studies revealed that identical twins typically have no more than a 7-point IQ difference, making this case astounding. Differences and similarities in intellect, reasoning, values, and more were observed among the sisters.

The vivid qualities of both twins have intrigued researchers. One researcher mentioned, "It is striking that the twins showed substantial differences in cognitive abilities that have been linked to strong genetic influence.” The study considered that the US-raised twin had concussions when younger, which could have affected her lower IQ. However, their different upbringings highlight the unique abilities identical twins can possess. The researchers also noted that many traits were similar despite their different environments and upbringings.

“Notable is that both twins are distinctively high on conscientiousness- indicating that both are purposeful, well-organized, dutiful, and achievement-striving,” one of the researchers wrote. An example to explain the same was also shared. The twin raised in Korea was exposed to a more loving, gentle and healthy family while the other faced hardships with her adoptive family and parents. Although the latter is enough to cause a variety of differences in each twin’s stature, they exhibited similar scores for self-esteem and mental health. In conclusion, the authenticity despite the similarity among identical twins is remarkable and opens up a large avenue for further exploration.