The idea that intelligence is mostly in your genes is surprisingly persistent. Some people still seem to think your IQ is fixed at birth, as if it were like an internal serial number you carry for life. But as we explain in The Psychology of Great Teaching, the old nature-versus-nurture debate has long been outdated. Reality is more complex. Our genes set the stage, but it’s the environment that determines how the play unfolds. Education is one of the strongest forces shaping that process.
A new study I came across via Gerard Govers illustrates this beautifully. Jared Horvath and Katie Fabricant collected all available data on identical twins raised apart. This included 87 pairs in total. They didn’t just compare their IQ scores, but also their schooling. That’s striking, because many classical twin studies barely took education into account. Yet we now know schooling can have a measurable impact on IQ.
The researchers divided the twins into three groups: those with similar educational backgrounds, those with somewhat different academic backgrounds, and those with very different educational backgrounds. The results were clear. Twins who received similar schooling differed by only 5.8 IQ points on average, about the same as twins raised together. But for those who had very different school experiences, the gap widened to 15 points.
In other words, the further their education diverged, the greater their IQ difference became. Even genetically identical people aren’t immune to the influence of schooling — for better or worse.
Horvath and Fabricant draw a compelling conclusion: if education can create such large differences between people with exactly the same DNA, we should be much more careful with sweeping claims about the heritability of intelligence. As I wrote above, it’s not nature or nurture, but how the two continuously interact.
And that’s actually good news for teachers, students, and policymakers alike. Because it means that learning, teaching, and creating opportunities truly matter, we can make people smarter. Literally.
A much larger study on over 1000 pairs of twins got a very different result.
Estimating Classroom-Level Influences on Literacy and Numeracy: A Twin Study
Katrina L. Grasby, Callie W. Little, Brian Byrne, William L. Coventry, Richard K. Olson, Sally Larsen, and Stefan Samuelsson
Journal of Educational Psychology, Vol. 112, No. 6, pp. 1154–1166
https://doi.org/10.1037/edu0000418
“We took advantage of large twin samples in Australia and the United States to compare the similarity of twins who either shared or did not share a classroom with their cotwin. We found that twins in separate classrooms were almost as similar in achievement as those who were placed together.”
Thanks, I’ll check but do check this study -> it discusses the element of raised apart, not only separate classrooms!