Adopted children may be slightly more intelligent than their siblings who were raised by biological parents, according to new research published in the Proceedings of the National Academy of Sciences. The recent study from Sweden tackled the heredity of intelligence with some interesting results. Researchers found that, among hundreds of cases where biological siblings were raised in separate households, the adopted children demonstrated an average IQ score of 4.4 points higher than the children raised by their natural parents.
Studying men in Sweden
In Sweden, men are legally required to take an IQ test between the ages of 18 and 20 upon enrolling in the military. Within that pool of IQ information, researchers found 436 instances in which two male siblings had been raised by different parents: adoptive and biological. Knowing that IQ is largely an inherited trait but that it's also considerably affected by socioeconomic circumstances, the researchers decided to use the opportunity to compare IQ scores between men who were linked genetically but grew up in separate environments. According to the authors of the study, they factored in the education levels of the adoptive and biological parents along with those of the siblings.
Why the difference?
So why exactly were the adopted siblings found to have a higher intelligence quotient than the others on average? The study found the difference was mainly about the parents' levels of education. Since most of the adoptive parents had slightly higher levels of education (meaning they had been in school for longer or had attained a higher degree) and provided a moderately better socioeconomic environment, the adoptive siblings' IQs were higher. The largest difference in IQ scores between siblings was 7.2 points – a hefty disparity when it comes to education and income expectancies.
"The more educated the adoptive parents are, the bigger the advantage for the child," said co-author of the study, Eric Turkheimer. "Even in the presence of genetic differences among people, improving the environment helps children's cognitive ability."
These IQ discrepancies were also true in cases where the biological parents were more educated than the adoptive parents. In these cases, the siblings raised by biological parents had IQ scores of up to 3.8 points higher than the adopted brothers.
The study confirms that environment can influence a person's intelligence, but it also sends a positive message about adoptions. Placing children in improved environment truly can make a quantifiable difference in their lives.