In the 1980s, New Zealand intelligence researcher James R. Flynn identified a consistent rise in IQ scores across the world throughout the 20th century. This became known as the Flynn Effect and was initially interpreted as evidence of humanity getting smarter—perhaps thanks to better nutrition, education, and healthcare.

But by the 1990s, the trend reversed.

The first major alarm came from Norway. Because of its compulsory military service, the country had amassed a massive database of cognitive testing—covering more than 730,000 young men from 1962 to today. What researchers found was stunning: IQ scores peaked among those born around 1975 and have been declining since. The average drop is about 7 points per generation.

Flynn himself later confirmed similar trends in the UK, where teenagers in the 2000s tested lower than their 1980s counterparts. And it wasn't just a fluke—researchers across the world observed the same pattern in developed countries.