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Except that those "on average" slightly better visual/spatial abilities are present before most of the testosterone kicks in.
Something worrisome is going on because they tracked a decline even within families, so no influence from migration or higher IQ women having fewer children etc., although I think those things have an influence. That's the benefit of a longitudinal study.
Perhaps it's something in the environment, or in how children are now being reared. Yes, there's a correlation of upwards of 60% (and probably more) of intelligence with genes, but something environmental, perhaps neo-natal, may also be involved.
Or, the parents to be were exposed to something which caused mutations in the genes governing intelligence, or "switched" them off.
I've always had a hunch that all the drugs ingested by some people when they were teen-agers, and immoderate use of alcohol as well, has had an effect on the number of children born with developmental delay, learning problems, autism, etc.
We'd better find out what it is. If the latter turns out to be the cause, the science deniers will be out in full force. They wouldn't want to admit they were wrong in saying it was all harmless.
While we're at it we'd better find out why sperm counts are dropping.
Non si fa il proprio dovere perchè qualcuno ci dica grazie, lo si fa per principio, per se stessi, per la propria dignità. Oriana Fallaci