I'm surprised by this recent Norway IQ study. Before 1975, later born children within a family scored higher. After, later born children scored lower. Unless I'm missing something, dysgenics shouldn't play a role here. What happened?
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This would also indicate that the decline is not due to differences from one family to the next--it looks like some change that's affecting society at large.
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Here's a possibility: smarter siblings increasingly avoided taking these tests in the cohort that was born after 1975? This is a military test that supposedly everyone must take, but I'm wondering if that's actually the case.
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Alternatively, people in more recent years are increasingly blowing off the test? Nutrition is also a good possibility. Whatever is causing declines in sperm counts (presumably some chemical exposure?) might be causing other problems.
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Replying to @HbdNrx
Declining participation was considered in the paper. Seems like it is happening, but mainly at the low-end of the distribution. Researchers controlled for this effect in order to reach the conclusion.pic.twitter.com/L4mEhkOjIs
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Replying to @CapHoratius @HbdNrx
These are the potential causes which were offered in the paper. The numbers in brackets are from a survey of intelligence researchers, asking which are most likely. Take your pick I guess…pic.twitter.com/4xvinZh5hU
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Replying to @CapHoratius @HbdNrx
I'm not quite sure why migration is included in this, since the only way that migration could have an environmental effect within families would be through one of the other mechanisms. (For example, the presence of migrant children making the education system worse).
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Seems like it would be a very small effect (just not high enough numbers to change much), but what if some of these siblings are actually half-siblings...
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Replying to @HbdNrx
I think there'd need to be an implausible amount of undetected interracial cuckoldry going on for that to be the main explanation
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