Like members of all other scientific communities, researchers on aging “form their divergent individual practices partly through interacting with nature and thinking by themselves, partly by borrowing from and lending to others.” Part One of Crossing Frontiers stressed that the roots of “modern” gerontology were very diverse. With the proliferation of journals and handbooks, the creation of research centers, the migration of investigators from a growing number of disciplines and professions, and increasing incidences of specialization and boundary-setting disputes, the field acquired the intellectual and institutional hallmarks of an emerging, occasionally fragmenting, scientific collective enterprise.

Even greater intellectual and institutional branching occurred during gerontology's early years than has been indicated so far. To wit:

In 1939, Sidney L. Pressey and Raymond G. Kuhlen issued Life: A Psychological Survey. The book placed more emphasis on the importance of cultural and socioeconomic factors on late-life development than did the contributors to Cowdry's Problems on Ageing, published the same year. Others thereafter began to advance arguments along the same lines. Leo Simmons's The Role of the Aged in Primitive Societies (1945) offered rich ethnographic evidence demonstrating how different types of cultures produced distinctive types of attitudes and expectations about growing old. Seizing on the significance of societal milieu, Kuhlen subsequently called into question most of the existing research on the relationship between intelligence and aging. Cultural change, he claimed in a 1963 article, “contaminates” both cross-sectional and longitudinal studies by not taking account of the effects of “change in cognitive stimulation which will differentially affect different age groups.”