alt Hacker NewsIQ 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.
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.