Don't want kids? It could mean you're smarter than your friends.

We have (sort of) bad news for anyone who has kids or is planning to start a family.

We don’t know how to say this, so we’ll just come out with it: a recent study from Iceland has found that your childless friends may be smarter than you.

The research from deCODE, a genetics firm in Reykjavik, found that the group of genes that predispose people to a higher IQ, became rarer in the country between 1910 to 1975.

The researchers used a database of over 100,000 Icelanders to look at how the genes that affect your likeliness of getting an education appeared in the population over time. And there was a shallow decline over the 65 year period.

The main point is this: the genes involved in education affected fertility. Basically, people who carried more ‘education genes’ tended to have less children.

So the scientists concluded that the ‘education genes’ had become rarer in the population over time, because better educated people were having less children.

“It isn’t the case that education, or the career opportunities it provides, prevents you from having more children,” said Kari Stefansson, who led the study. “If you are genetically predisposed to have a lot of education, you are also predisposed to have fewer children.”

But the effect is really, really, really small. Writing in the Proceedings of the National Academy of Sciences the researchers have estimated that it really only corresponds to a drop in IQ of about 0.04 points per decade. If you add in all the genes that contribute to education, the figure might rise to 0.3 points per decade.

However, Stefansson said the effects overtime could be a lot more serious.

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“The cumulative effect over time means this is going to have a dramatic effect on the genetic predisposition to educational attainment, and unless something comes along to counteract that, it could have a profound effect on educational attainment in our society,” he said.

But the changes in education could override any genetic effects, as IQ scores rose by nearly 14 points between 1932 and 1978, as education improved.

Which means this is a problem for your future self. Phew.

As you were, people.