> Can you properly analyze the reasons behind this without going into ethnic differences in IQ?

The article mentions a Norwegian study [1] measuring an IQ decline within families.

So it looks like the cause must be environmental.

My pet theory is that reading as an activity has been replaced by the consumption of audiovisual content.

[1] https://www.pnas.org/content/pnas/115/26/6674.full.pdf

See my comment above, the data in the Norwegian study is VERY suspect

Thanks for the heads-up. Yes this difference in sampling method changes everything.

I'd also wager that our increasing usage of computers (including/esp. the handheld kind) to perform tasks that used to require us to use our brains plays a role (e.g., I don't bother calculating the tip at a restaurant anymore, I just have a phone app figure it out for me).

And this will only get worse... until we're like the Eloi, surrounded and dependent on technology no one understands anymore.

That head-in-the-sand approach doesn't make these issues go away.