They’re not societies, but these groups were first systematically defined in a 1928 essay by Karl Mannheim that ties their development to the “tempo of change.” William Strauss and Neil Howe devised a theory of these groups in which four of them represent a cyclical “saeculum.” The imprint hypothesis highlights (20[1])the role of historical events in defining these groups. The most studied example of trauma shared between these groups is Holocaust survivors, as researched in (*) epigenetics. Slang and technological development can contribute to namesake “gaps” between these groups. Pew Research Center uses 1997 as the cutoff for one of these groups because they have little to no memory of 9/11. For 10 points, name these groups of people born around the same time, such as Millennials and Zoomers. ■END■