A recent study found higher IQ levels for adopted children than for their siblings who remained with biological parents.
The difference of approximately four IQ points seems to stem from higher educational levels in adoptive parents.
“The more educated the adoptive parents are, the bigger the advantage for the child,” said study co-author Eric Turkheimer, a professor of clinical psychology at the University of Virginia in Charlottesville. “Even in the presence of genetic differences among people, improving the environment helps children’s cognitive ability.”
The study was only designed to discover the association between adoption status and intelligence. It was not proven that adoption actually raised IQ scores.
In the research that was published in the Proceedings of the National Academy of Sciences, the authors analyzed data from sets of Swedish male siblings, as all males there are required to take an IQ test between ages 18-20.