WaPo graph labeled “The history of left-handedness” among Americans, by birth year. It dips from 5 to under 4 between 1890-1910, then in a straight line up and to the right until it levels out near 12% around 1960, and stays flat from there through 2000.
https://media.mstdn.social/media_attachments/files/114/344/339/480/685/476/original/97321db4dcb6c4c3.png