Identical twins who were raised apart may have IQ differences similar to those of total strangers, according to new research. The findings suggest that variations in IQ may be less about genetics and more about schooling.

The heartbreaking separation of twin siblings is a rare occurrence, and only nine large group studies have been published to date.

In the past, researchers have concluded that identical twins raised apart have many matching traits, including similar IQs, suggesting that IQ (a sign of intelligence) is largely determined by nature, not nurture.

Not so fast, argue cognitive neuroscientist Jared Horvath and developmental researcher Katie Fabricant. These two have crunched the numbers again, and this time, they've included a key overlooked factor: schooling.

When the researchers divided 87 twin-pairs into groups based on similar and dissimilar schooling backgrounds, they found IQ differences across the spectrum.

The gaps in IQ scores grew in tandem with educational differences, the authors say, "enough to transcend specific teachers or peer groups."

Twins that were raised apart and who went to significantly different schools showed IQ patterns more similar to strangers (a roughly 15-point difference).

There were only 10 twin-pairs in the study with school experiences that met suitable criteria, making for a small sample size that places limits on the study's conclusions.