Posted on 05/12/2022 at 2:48 p.m.,
Reading 2 mins.
Two monozygotic twins separated at the age of two and raised in two different countries have turned science upside down: their intelligence quotient difference is 16 points. A result that contradicts in all respects the previous tests carried out on the twins.
One is American, the other Korean. Two twin sisters born in Seoul and then separated at the age of two showed great cognitive disparities following a battery of tests. Scientists are trying to understand the reasons for this discrepancy.
Monozygotic twins: the influence of the environment
Two monozygotic twins, born in Seoul, South Korea in 1974 and then separated two years later, divide science.
One was adopted by a couple living on the other side of the planet, in the United States, while the other stayed with her biological family in Korea.
Thanks to the South Korean program for the reunification of members of the same family, they found each other recently and, on this occasion, agreed to take a series of tests intended to assess their intelligence quotient, their character traits, their mental health and their medical history.
The results revealed that the IQ of the twin raised in the United States was significantly lower than that of her sister raised in Korea: a difference of 16 points was recorded.
The discovery, published in the journal Personality and Individual Differencescontradicts previous work on monozygotic twins, which states that even in the event of separation at birth, the average difference in IQ value does not exceed 7 points.
“It is striking that the twins showed substantial differences in their cognitive abilities, normally linked to a strong genetic influence”confide the scientists, while the duo cultivated many common points: character traits and health problems in mind.
However, it is difficult to draw hasty conclusions on the subject: is it education, culture, family that have such an impact on cognitive abilities? For the researchers, caution is in order because the twin raised in the United States has a much more fragile health: she suffered three concussions. This type of injury caused by a strong shock can disrupt the functioning of the brain.
According to the researchers, further studies are needed to find out more.
Identical twins and fraternal twins: what’s the difference?
Identical twins, false twins, monozygotic, dizygotic… Many terms exist to designate twin pregnancies.
In the case of monozygotes (also called homozygotes), a single egg meets a single sperm.
Once fertilized, the ovum becomes an egg which will split in two and lead to the formation of two embryos. The latter will give rise to two fetuses of the same gender with strictly identical genetic heritage.
These monozygotic pregnancies can be monochorionic (one placenta) or bichorionic (two placentas). There may be one amniotic sac (mono amniotic) or two amniotic pouches (bi-amniotic).
Conversely, fraternal twins (dizygotic) are the result of two simultaneous fertilizations of two ovules by two different spermatozoa. They evolve in two amniotic sacs and have two distinct genetic identities.
Slide: The 8 Forms of Intelligence