Assuming IQ tests are fairly good (they’re probably not, but that’s a separate issue), there is one major conclusion to be drawn from this — even when you control for nature, extrinsic factors (nurture, environment) can have an effect at least this extreme.

In this case, nurture is several concussions

You can always degrade genetically highly potential humans to a lower level with environmental factors. But you can never lift up a human to a high level when the genetic prerequisites are not met.

I would think the number of people maxing out their IQ is pretty small. There's a whole lot of work, including that done by HN readers, that's pretty rote. Not too much "deep thinking" required to clone an application, follow a tic-list, ...

Similarly, the number of people who can't be lifted to "a high level" is similarly small. I assume you don't mean "those who can't function on their own", so you're discussing the mass of people who toil along in "typical jobs for typical people". Healthy, fully-formed w/o congenital defects, thankfully, is common and usually sufficient.

Edit: these tests are culture-specific. Doubt too many of the readers of HN would look functional on one for Inuit or Japanese.

"Never" is a strong word. Perhaps we will be able to fix those missing faculties in the future somehow. We certainly learnt how to fix many other congenital conditions.

My wife was born with a heart defect that would have killed her 60 years ago. 30 years ago, it was already fixable and now she can live a pretty normal life except for "do not exercise too much". Maybe we will be able to do the same in 2040 or 2050 with people who were born with various mental defects.

Maybe there will be a magic pill that makes everybody much more intelligent. We are only using a few percent of our brain after all. Until then I assume that the evidence presented by mainstream psychology is correct which says that between 50% and 80% of IQ is inherited.

It need not be a pill. It might be genetic manipulation of an already living organism. As of today, the tools like CRISPR aren't very nimble, but who knows what tools will be used in 2040 or 2050 for that purpose. The difference between them and today's CRISPR might be the same as difference between Intel 8080 and Intel Pentium.

You can turn this around to see the massive positive impact of environmental factors... There were plenty of people around before the invention of written language who could not have even taken one of these tests. Is that an environmental degradation, or proof that we've largely succeeded in improving human intelligence through cultural inventions?