It is called the Flynn effect after James Flynn, who discovered it.

ECONOMIST: Disease and intelligence

One Saturday in November of 1984, James Flynn, a social scientist at the University of Otago, in New Zealand, received a large package in the mail.

NEWYORKER: None of the Above

In Act II, for example, when Father Flynn consoles Sister James and earns her support, the braiding of their lines creates romantic frisson between the two.

WSJ: A Re-'Doubt'-able Effort | John Patrick Shanley | Cultural Conversation by Judith H. Dobrzynski