IQ levels have decreased in the 21st century, it's known as the reverse Flynn effect, Norway did a large scale study on almost a million people because they have a lot of military data and accounting for genetics IQ peaked for people roughly born in the late 70s and has been declining since. We've actually wiped out a fair amount of 20th century gains in intelligence.

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dredmorbius 7 hours ago | parent [-]

Oddly: this coincides with the period in which leaded petrol has largely been phased out on most countries. The use of lead in motor-vehicle fuel is though to have shaved a few points off IQ by itself.

Much as with some other widespread phenomena that come to mind, it's an observed trend the reverse of what might otherwise be expected.

	▲	iamnothere 5 hours ago \| parent [-]
		Lead exposure can damage the reproductive system, so perhaps it’s to be expected if a whole generation of parents were exposed to leaded gasoline. Theoretically this effect would wear off with the next generation, unless there was durable damage to genetics that gets passed on. A cursory search suggests this may be possible, but I’m not a biologist or geneticist.