>It's not that dumb people are having more kids than smart people, to put it crudely. It's something to do with the environment
This is false. The correlation between cognitive ability and number of offspring is negative. Here's a link to a systematic review on this topic: http://sci-hub.tw/https://www.sciencedirect.com/science/arti... that covers many datasets, where you can see the negative correlations on page 114 (8 in this pdf), which vary from -0.01 to -0.27 depending on the group in question. Although this does not rule out an environmental influence by itself, it's dishonest to simply dismiss it as the article has done.
> In a separate study that has not been released, he and his colleagues looked at existing research in an effort to demonstrate that staying in school longer directly equates to higher IQ scores.
Keyword here is "an effort to demonstrate". That sounds like they really want the results to come out in their favor, and we know that is not a good sign. They can mess around with correlation and causation and p-values and subgroups and framing all they want, but whatever they come up with will contradict a lot of the existing literature in this area in order to push their agenda.
Let's not forget that IQ tests are just statistical analyses, while we still lack a bottom-up explanation of intelligence.
But then sometime starting around the mid 90s it began to reverse in developed nations. And by reverse, I mean IQ's began declining - not approaching some sort of asymptotic 0 level of growth. So, if we normalize for age, an average person born in the 70s will have a higher IQ than an average person born in the 90s.
 - https://en.wikipedia.org/wiki/Flynn_effect
Firstly, this is such a massive and important finding, even cessation of the Flynn effect would be, that one has to wonder why we haven’t seen it published until now.
Secondly, one of the frustrating parts of being a statistician is that a 90% explanation of nearly every effect comes from some common-sense factor. So much so that it raises suspicions when a strong effect is shown along with a series of specific and fairly complicated ‘anti-explanations’. The article seems more interested in disproving the ‘idiocracy’ effect than finding some alternative explanation.