People have gotten taller and healthier because of better nutrition, there is no reason to believe people haven't gotten smarter as well.
Null hypothesis? By default we don't assume presence of changes, in the absence of reasons for that, and those reasons - that nutrition is causing IQ growth - need to be explained.
There shouldn't be no reasons not to assume something, it's not enough. Sorry for triple negative.
This isn’t a by default issue, this is claiming counterevidence to increase in intelligence that justifies rejecting the validity of IQ in measuring intelligence because it is increasing. The null hypothesis doesn’t support that, only independent evidence of intelligence not increasing would.
The idea that evolution stops at the neck seems completely laughable to me.