Many observers see today's American nuclear family as having undergone revolutionary change and as being in a process in which it will become qualitatively different from what it was 50 years ago; some think of it as an "endangered species." Weiss, however, sees it as having undergone a steady process of gradual evolutionary change. The seeds of the American family of the 21st century, she argues, were present in the mid-20th century. Her analysis is based on data from the longitudinal studies of the Institute of Human Development (IHD) at the University of California at Berkeley. The institute's study subjects were interviewed repeatedly over decades, between childhood and late middle age. As a result, Weiss notes, "we are able to follow the effects of the fifties family pattern over time, permitting a much more nuanced and deeper understanding of postwar family life than the one-decade 'snapshot' view historians persist in portraying."