It's clear that brains vary, of course, but 'intelligence' is too broad a term to say, quantitatively, to what degree a person possesses it. The term encompasses:
- The ability to acquire new knowledge quickly, or to learn difficult things at all.
- The ability to, given time, make nontrivial deductions from given data.
- The ability to make rapid deductions in short periods of time about given data.
- The ability to generate multiple unrelated solutions to a problem.
- A high level of verbal proficiency.
We mean all these things to different degrees at different times when we use the term; and although these are not orthogonal concepts, they clearly do not exist in a one-dimensional space.
Certainly if IQ is taken to mean 'the raw, unchanging potential of a mind', the Flynn effect is inexplicable given that the timescales involved are far too small for our neurobiology to have adapted evolutionarily. Given that it means very little other than 'the ability to pass IQ tests', the Flynn effect is perhaps not surprising at all.
It's pretty much conspiracy sort of stuff.
A. It's quite a stretch that a whole scientific community can't create a test for IQ and get past the tired issues brought up 50+ years ago.
B. The concept brains unlike heights, hair, body shape etc etc etc are all the same is pretty ludicrous.
There is lots of stuff on the Flynn effect, I'm sure people can google it for themselves. But at the end of the day why is it so strange a test given to people in the 1960s scores differently for people in the 2010s. It is such a strawperson argument.
IQ's about relativity and ability in the current environment.