Some speculate it happens b/c more educated/smarter people have fewer children. But this may not apply when you control for sibling effects.
Blood lead levels (https://www.motherjones.com/wp-content/uploads/2018/01/blog_lead_crime_mainchart.gif) peaked for both boomers and GenX, but drastically decreased for the GenX/Millennial transition, but the above study shows cohorts born from 1961 to 1990, and shows that the millenials (presumably with the lowest lead levels!) also have the lowest raw IQ. [the study above is for Norway—I don’t know how much lead was present in Norwegians mid-century, but it appears that Norway had a lead problem just as the rest of the states had.
In the new study, the researchers observed IQ drops occurring within actual families, between brothers and sons – meaning the effect likely isn’t due to shifting demographic factors as some have suggested, such as the dysgenic accumulation of disadvantageous genes across areas of society.
Instead, it suggests changes in lifestyle could be what’s behind these lower IQs, perhaps due to the way children are educated, the way they’re brought up, and the things they spend time doing more and less (the types of play they engage in, whether they read books, and so on).
Another possibility is that IQ tests haven’t adapted to accurately quantify an estimate of modern people’s intelligence – favouring forms of formally taught reasoning that may be less emphasised in contemporary education and young people’s lifestyles.
It is worth noting that air and water pollution levels are significantly lower now than several decades ago, and organochlorine pesticides have been phased out (in favor of organophosphate pesticides—organochlorines seem to cause greater hits to IQ and epigenetic age), so environmental pollution probably isn’t as important here as other factors. (at the same time, it’s possible that people have been exposed to increased levels of possibly-IQ-decreasing pollutants such as microplastics or flame retardants)
Perception of reduced intelligence/creativity could also simply be caused by longer life courses (the social capital gerontological glut—https://palladiummag.com/2020/10/10/the-social-capital-stall-behind-americas-gerontocracy/ - which causes many young people to define their life paths around this glut and careful about what they say for fear of alienating this glut) causing people to take longer to grow up before they can get in positions where they can produce widely-read important work (which is related but not identical to aging of the population). People are often not at their most organic selves when trying to “reach a social bar” where the average age of the people who make it (eg R01 investigators, university faculty positions, leadership/management positions) only continue to increase. I’m not sure if this applies to much of the valid intelligence-showing work that is produced online and then doesn’t get deleted, but it certainly seems like people have a tendency to fail to archive everything they’ve produced online during their years of peak intelligence.
Overall, we know that real intelligence, g, is slowly declining in Western nations and China (possibly in other locations as well). For a good, easily understandable, explanation of the FE and the decline in g, read At Our Wits’ End: Why We’re Becoming Less Intelligent and What It Means for the Future, by E. A. Dutton & M. A. Woodley of Menie. Exeter, UK: Imprint Academic. If you want a reasonably long list of papers that have addressed the decline in intelligence, ask and I will post a list.
Have you looked into the reverse flynn effect? eg see https://www.sciencealert.com/iq-scores-falling-in-worrying-reversal-20th-century-intelligence-boom-flynn-effect-intelligence
https://marginalrevolution.com/marginalrevolution/2018/06/reversal-flynn-effect-environmental.html
https://www.pnas.org/content/115/26/6674 (shows reverse flynn effect for norwegian cohorts)
Some speculate it happens b/c more educated/smarter people have fewer children. But this may not apply when you control for sibling effects.
Blood lead levels (https://www.motherjones.com/wp-content/uploads/2018/01/blog_lead_crime_mainchart.gif) peaked for both boomers and GenX, but drastically decreased for the GenX/Millennial transition, but the above study shows cohorts born from 1961 to 1990, and shows that the millenials (presumably with the lowest lead levels!) also have the lowest raw IQ. [the study above is for Norway—I don’t know how much lead was present in Norwegians mid-century, but it appears that Norway had a lead problem just as the rest of the states had.
It is worth noting that air and water pollution levels are significantly lower now than several decades ago, and organochlorine pesticides have been phased out (in favor of organophosphate pesticides—organochlorines seem to cause greater hits to IQ and epigenetic age), so environmental pollution probably isn’t as important here as other factors. (at the same time, it’s possible that people have been exposed to increased levels of possibly-IQ-decreasing pollutants such as microplastics or flame retardants)
Perception of reduced intelligence/creativity could also simply be caused by longer life courses (the social capital gerontological glut—https://palladiummag.com/2020/10/10/the-social-capital-stall-behind-americas-gerontocracy/ - which causes many young people to define their life paths around this glut and careful about what they say for fear of alienating this glut) causing people to take longer to grow up before they can get in positions where they can produce widely-read important work (which is related but not identical to aging of the population). People are often not at their most organic selves when trying to “reach a social bar” where the average age of the people who make it (eg R01 investigators, university faculty positions, leadership/management positions) only continue to increase. I’m not sure if this applies to much of the valid intelligence-showing work that is produced online and then doesn’t get deleted, but it certainly seems like people have a tendency to fail to archive everything they’ve produced online during their years of peak intelligence.