Thanks for the most erudite comment that’s ever been posted here. I am rapidly getting out of my depth on this. I’ve read a good few of the arguments on this, but only in a pretty superficial way (such as reading the Amazon reviews of Flynn’s book and googling)

Your argument for environmental enrichment is very plausible. If there was a change in people’s thinking capacity over a hundred years or so, then it would surely be the most likely cause. I think it would be a fascinating research topic.

The data for change over time is just much harder to evaluate. The Neissen quote comes from Wikipedia. which gives a very brief explanation of research methods that had been used to compare scores over time. I would hope the data is based on more sophisticated data gathering than just looking at raw scores. I completely agree with you that the general population’s genetic capacity for intelligence is unlikely to have changed.

From my limited understanding of the concept, if the measure of IQ has to be standardised round 100 then a rise in the average IQ can never be demonstrated because it will always be 100.
However, if raw scores are taken, then this is changing the whole basis of the IQ concept and its built in balances.

I think IQ is particularly vulnerable to pop science distortions, exemplified by how easy it is to boil a complex scientific debate down to the idea that people are just getting “smarter”. Most people who use the concept have no concern for how the statistics are generated. It’s only the pop science that gets through.

There is ample evidence that a jump in IQ score that results from taking an individual from an intellectually-understimulated environment (such as an orphanage) and providing that individual with stimulation. This old data would fit with the postulated explanation for the Flynn effect.

Conversely, an early study on the stability of an individual’s IQ score over the lifespan found that the children of barge people in England demonstrated a longitudinal drop in score because their environment was relatively less stimulating as they grew older.

Were the comparisons over Neisser’s 30 year gap made of individuals of similar ages in each sample? Did Neisser say that the raw socres had jumped by 21-35 points or that the quotient had made that jump? I suspect the former because the population’s genetic endowment is unlikely to have changed even though the level of technologically-thinking stimulation has risen.