Well, we can easily measure the differences in average height due to having an objective physical difference to see.
However, IQ tests have changed substantially over the years as far as my understanding goes; to the point that its likely the one I did years ago wouldn't be the one I would be given now. How do we rule out that having an effect? Follow on question: say I take an IQ test at the age of 80, and for the most part my brain functionality hasn't changed or degraded significantly. Will IQ tests, taking into account the changes necessary to 'accurately measure average intelligence' (really fascinating it did that as I am thick as heck in general, but certain aspects relating to the test really appealed to my interests as I had then - particularly the reading, which until the year I took it I immensely struggled with), still note my score as above average, or will mine being reduced - seemingly suggesting my, well, general intelligence has somehow decreased? How can we be sure newer tests aren't biased in some regard as well?
Intelligence tests are supposed to be consistent over time, and usually are (on average), but there are all kinds of things that can bias them (which the test writers perpetually struggle to mitigate) and some intelligence tests are better measures of G than others.
As well as that, one of the studies done recently in Kenya, in 2003, mentioned in that page, that parental literacy and family structure were likely hypothesis as to why these children had higher IQ scores. So are these children more 'intelligent', or better educated?
I'm not sure. That may be disconfirming evidence but, you know, there needs to be consistent disconfirming evidence and also a good replacement explanation of what causes a phenomena, before the existing explanation is discarded.
Apologies, I am quite poor at finding studies and doing that type of research - I only knew about the Shaun video from discovering his channel for other reasons. Could you point out these academic reviews and articles about the state of the intelligence fields, as you are so much more familiar with them than me?
It can be tricky getting access to academic articles sometimes because of the pay-gating of the large journal publishers, but you can usually get them through your local library.
Annual Reviews is good place to find high level summaries of research about almost anything.
They have one on intelligence from 2012. There is also the
book chapter I linked in my first post in this thread. As access to those might be difficult, here is a full text link to a
short article about the topic from 2019 (it argues against general intelligence, fyi) which summarizes prior research and cites lots of things, so you can follow its breadcrumbs if you're so inclined. Also,
google scholar is your friend if you ever want to find things like this in the future.
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To clarify; I am not of the opinion that general intelligence
definitely governs human success and flourishing, just that there is a
there there. A meaningful phenomenon has been observed, there has been a good faith effort to understand it, and it
might be that general intelligence is a durable personal characteristic.