different spatial tests are all basically testing the same underlying ability—and that this ability is only partly explained by general intelligence. This means that spatial ability is, to some extent, independent: you can have better (or worse) spatial ability than your general intelligence might suggest. The results also suggest that about a third of the differences in people’s spatial scores can be explained by genetics.
A team of researchers led by Kaili Rimfeld of King’s College London studied more than 1,300 pairs of twins to figure out to what extent genes contribute to spatial ability.
But first, they had to figure out which aspect of spacial reasoning to test them on. The researchers scoured the scientific literature to find all the different tests that had been used to assess spatial ability and ran pilot studies using them. They took out any tests that were too easy or difficult and any tests where the same people scored inconsistent results when taking the same test twice. The team also looked at the similarity of people’s scores in different tests—if the scores were very similar, they took out the redundant tests. By doing this, they boiled spatial ability down to 10 core tests.
Comparing the results of the identical and fraternal twin pairs found that 69 percent of the differences in spatial test results could be explained by genetic similarity. Of the remainder, the majority—23 percent—was explained by individual experience.
That only leaves a small bit of ability to be explained by the environment that the twins shared. The researchers emphasize that these estimates are unique to this population: in a less equal environment than the UK, genes might explain less of the difference.
The researchers also compared the genetic overlap with general intelligence. They found that after controlling for general intelligence, 30 percent of the differences in spatial scores could be attributed to genetic differences.