> IQ scores in most of the Western world began reversing sometime from the 90s to early 00s. [1] That link is for the US but similar stuff has also been observed in most of every Western/OECD nation.
I wonder to what extent demographic shifts account for the observed reversal? It would be interesting to tease out what happens where composition remains constant, i.e. Poland. Though I doubt this explains the entire effect.
> By contrast they're still rapidly increasing in the 'Global South'.
seems like the Flynn effect doing its thing just as it did in western countries in the 20th century.
Just because smart people tend to have fewer children (because, for instance, they delay it due to schooling and career demands) doesn't mean genes for intelligence are necessarily being selected against.
There's several reasons why this might not be the case, including that our premise is simple heritability and not genetic determinism, which is a different concept. I get where you're coming from now though.
People beat around the bush but the heritability of IQ is extremely high, modern studies put it around 80%. So if one group has an IQ of 140 and another of 100, it'd imply about 32 of those 40 points are generally able to be explained by genetic factors. For some contrast that tends to be around, or a bit above, the estimated heritability for height.
And so you'd see that easily in a single generation. It'd be akin to if tall people (or short people) began removing themselves from the gene pool in significant quantities. You'd immediately (well at least once people reached their adult height) see a significant increase or decrease in average heights.
This isn't true; 80s and 90s-vintage twin studies put it around 80%, but those numbers have been slashed; even hereditarians don't stand by them anymore. Molecular genetics results (contested by hereditarians, in fairness) situate it closer to 15-30%. David Bessis has a good piece about this.
And that's before you get to the slippery definition of what "heritability" means. It does allow you to use the words "explained by genetic factors", but in a very specific way, one in which the number of hands you have isn't similarly explainable, but how much TV you watch is.
That's quite a meaningless statement. Molecular genetics is in its infancy and so you're appealing to absence lack of evidence, which exists for most of everything, as evidence of absence - quite nihilistic! A quick search similarly suggests rates as low as 10% for the heritability of (non-European) height based on molecular genetics, undoubtedly for the same reasons.
And we've already had this conversation and in spite of your obsession with bias confirming 'blogs written by very smart people' - the heritability of TV watching is zero. Actually lol looking this up, it turns out there has indeed been a study done on this [1], as part of a study on the heritability of sedentary behaviors in general. And yeah, it's zero.
You are right that the number of hands you have is not heritable, but is only because heritability is defined as the percent of variation in a trait, between populations, that can be explained by genetic factors. When basically everybody has two hands, there is no variation, so there is no heritability to measure. It'd be like discussing the heritability of hair color if everybody had black hair. It's not some sort of clever insight or retort, though I'm certain your blogs framed it as the wittiest thing ever.
This comment doesn't actually say anything. I get that you're unhappy with the comment that I wrote? But that's all I get from it.
The one specific claim you make here, that height has heritabilities measured at around 10%, is false. In fact, the comparisons between the steadfastly high heritabilities of simple physical phenotypical traits like height and complex behavioral characteristics is a big part of the current scientific conversation about behavioral genetics.
But you’re seeing huge effects in three years, not a generation.
The report notes “The change in mean scores that can be explained merely by the changing composition of the student body, however, never exceeds a few points.”
So for Portugal for example about 10% of the drop might be attributable to immigration. But the other 90% to something else.
The West is still mostly in the denial phase, so nothing is really being done, yet. As such, the effect is ongoing. The Flynn Effect (and its reversal) are measured in impact per decade. And numbers that seem small at first aren't necessarily so. For instance a 3 point decline per decade doesn't initially seem like much until you consider that IQ generally has an artificial mean of 100 with a standard deviation of 15. So 3 points per decade is 20% of a standard deviation per decade! That's enormous.
In the past an IQ of 85 was considered mentally retarded. This was changed in 70s to make normal intelligence 'more inclusive.' That's another way of stating that 85 is still the best threshold for mental retardation. So a reverse Flynn Effect of 3 points/decade means you're talking about going from perfectly average to mentally retarded in 5 decades.
And for many things, the effect will not be linear. If we take a test there's likely to be an exponential pattern where somebody of a certain IQ will get an answer correct e.g. 99% of the time, somebody a bit below 80%, somebody a bit below that 40%, and then somebody a bit below that will basically never get it correct beyond the point of statistical noise. Pair that with likely increased variance when looking at individual and relatively small societies, and it's fairly easy to imagine sharp swings being completely viable.
I wonder to what extent demographic shifts account for the observed reversal? It would be interesting to tease out what happens where composition remains constant, i.e. Poland. Though I doubt this explains the entire effect.
> By contrast they're still rapidly increasing in the 'Global South'.
seems like the Flynn effect doing its thing just as it did in western countries in the 20th century.