Wondered about that as well, but another article, linked in the original one, mentions the original study dismisses that hypothesis, since it happens between me

Wondered about that as well, but another article, linked in the original one, mentions the original study dismisses that hypothesis, since it happens between members of the same family : https://www.sciencealert.com/iq-scores-falling-in-worrying-reversal-20th-century-intelligence-boom-flynn-effect-intelligence https://www.sciencealert.com/iq-scores-falling-in-worrying-r... "In the new study, the researchers observed IQ drops occurring within actual families, between brothers and sons – meaning the effect likely isn't due to shifting demographic factors as some have suggested, such as the dysgenic accumulation of disadvantageous genes across areas of society"