I’ll start off by saying that it’s not because of genes. Reseachers found that IQ scores actually increased every 10 years for people born between 1962 to 1975. But, the tides shifted for people born after 1975. AKA me.
The decline in scores is attributed to environmental factors, according to CBS 13. These factors include “changes in the education system and media environment, nutrition, reading less and being online more,” says researcher Ole Rogeberg.
“It’s not that dumb people are having more kids than smart people, to put it crudely. It’s something to do with the environment, because we’re seeing the same differences within families,” he added.
To get data, a Norwegian study looked at the IQ scores of brothers who were born in different years. Scores differed between the siblings, which correlates more with the date of birth than genetic reasoning.
You can read more about the study here.