This chapter offers a new perspective on the development of theories of aging by proposing that the complexity of the aging process requires accounting for its multiplicity, specifically, its multiple time frames, multidirectionality, multidimensionality and interplay of factors, and multilevel infl uences. Complementing earlier proposals from life-span developmental psychology ( Baltes, Staudinger, & Lindenberger, 1999) and lifecourse research ( Elder, Johnson, & Crosnoe, 2003; Settersten Jr., 2003), we propose some key theoretical principles that should be considered in future research to advance our understanding of aging within the context of the social sciences.
Given the complexity of the phenomenon of aging, the breadth of research in this field, and the rapid development of this fi eld, we cannot present a comprehensive model of development and aging in this chapter. After decades of relying on cross-sectional studies in which insights into age-related changes were derived from age-group comparisons, a great number of longitudinal studies that enable a better understanding of development have been recently conducted. More than ever, there is a need to discuss how the empirical findings of longitudinal studies can be integrated and incorporated into aging theories. One of the major strengths of longitudinal studies is that they allow an analysis of intraindividual changes, interindividual differences in intraindividual changes, and their determinants ( Baltes & Nesselroade, 1979). We build the current chapter on this strength.